Prosthesis for a joint of a hand or wrist

Abstract

The present disclosure relates to a prosthesis (400) configured for implantation in a carpometacarpal joint in the wrist, the prosthesis comprising a first and a second implant part member (405a,b) configured to be screwed into a radius and metacarpal bone respectively. Each implant part member (405a,b) comprising an articulation member (420a,b) configured to be received in the bone fixation member (410a,b) in a releasable manner. The articulation members (420a,b) comprise orientation pins (423) configured to be inserted into bore sections of the bone fixation members 410a,b. When seated in the bore sections, the first portions of the articulation members (420a,b) with the orientation pins (423) are substantially centered along the central axes of the bone fixation members (410a,b), thereby forming common central axes extending through the bone fixation members (410a,b) and the articulation members (420a,b). The radius articulation member (420a) comprises a replacement articular surface configured for articulation with a replacement articular surface located on the metacarpal articulation member (420b). The radius replacement articular surface has (420a) a configuration that is asymmetric about the common central axis of the radius bone fixation (410a) and articulation members (420a). The bore sections have cross-section (419) extending perpendicularly to the central axis defining a first polygonal outline (429). The orientation pins (423) have cross-sections defining a second polygonal contour line, such that when the orientation pins (423) of the articulation members (420a,b) are seated in the bores of the bone fixation members (410a,b), rotation of the articulation members (420a,b) in relation to the bone fixation members (410a,b) is prevented.

Description

[0001] PROSTHESIS FOR A JOINT OF A HAND OR WRIST

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to prostheses of the joints in the hand and wrist and further a modular prostheses system for the joints in the wrist.

[0004] BACKGROUND OF THE INVENTION

[0005] The human wrist is made up of eight separate small bones (carpals) in two rows which connect the two bones (radius and ulna) of the forearm to the hand. The hand is composed of five long bones (metacarpals) within the palm which are attached to the bones in the fingers and thumb (phalanges). Ligaments connect all the small bones to each other, and to the radius and ulna. Articular cartilage covers the bone surfaces in all joints to act as a shock absorber and to provide smooth surfaces to thereby make motion easier and to protect the bone ends from friction when moving the joint. Damage to the articular cartilage may eventually lead to arthritis.

[0006] Several wrist joint prostheses are known. For example, during wrist hemiarthroplasty, one or more of the carpal bones in the proximal row of small bones at the base on the hand are replaced by an implant. The implant advantageously utilizes modular components in various sizes or shapes to match a patient's individual anatomy and thereby more closely mimic normal wrist motion. Durability of the hemiarthroplasty is dependent on prosthetic stability and thus the distal end of the radius must be capable of supporting the implant.

[0007] W02006 / 088412A1 discloses a wrist joint prosthesis comprising two prosthesis members, wherein the first prosthesis member comprises a first bone fixation member (first screwlike member) arranged to be connected to a radius bone of a radiocarpal joint and the second prosthesis member comprises a second bone fixation member (second screw-like member) configured to be connected to a metacarpal bone, e.g., metacarpal III. The first prosthesis member comprises a first articulation member shaped as a circular socket configured to cooperate with a second articulation member shaped as a sphere and forming part of the second prosthesis member. The spherical articulation of the wrist joint disclosed in W02006 / 088412A1 will closely replicate the patient’s normal range of motion, including a dart thrower’s motion. In some types of prostheses, the precise alignment of the articulation member is very important for the interaction of its replacement articulation surface with the opposing articular surface. This is so, regardless of whether the opposing articular surface is arranged on a natural bone of the joint or on an opposing replacement articular surface of a second implant part of the prosthesis. Furthermore, it is important that the precise alignment of its replacement articulation surface remains stable during normal use of the prosthesis after implantation.

[0008] SUMMARY OF THE INVENTION

[0009] The above objects may be achieved with a prosthesis for a joint in the hand or wrist in accordance with claim 1. Further examples are set out in the dependent claims, the description and in the drawings.

[0010] As such there is provided a prosthesis for a joint in the hand or wrist comprising a first implant part comprising a bone fixation member and a first articulation member, wherein the first articulation member is configured to be received in the first bone fixation member in a releasable manner.

[0011] The bone fixation member is configured to be screwed into a first bone of a joint of the hand or wrist, wherein the bone fixation member comprises a central axis A that extends from a first end to a second end of the bone fixation member. The bone fixation member further comprises an inner bore extending from a surface on the second end towards the first end of the bone fixation member. The inner bore comprises two or more bore sections being centered or substantially centered along the central axis A extending through the bone fixation member, wherein the first bore section is configured to receive an orientation pin arranged on the articulation member.

[0012] The articulation member has a first portion and a second portion. The first portion comprises the orientation pin configured to be inserted into the first bore section of the bone fixation member. When seated inside the first bore section, the first portion with the orientation pin is centered or substantially centered along the central axis A of the bone fixation member, thereby forming a common central axis AA extending through the bone fixation member and the articulation member.

[0013] The second portion of the articulation member comprises a replacement articular surface configured for articulation with an opposing articular surface. When the articulation member with the orientation pin is seated inside the inner bore, the replacement articular surface has a configuration that extends in three directions x, y and z, wherein - a first direction x extends parallel to the common central axis AA formed between the bone fixation member and the articulation member; and

[0014] - a second direction y extends perpendicular to the first extension x; and

[0015] - a third direction z extends perpendicular to both the first extension x and the second extension y, such that the replacement articular surface has an extension in the yz-plane that is asymmetric about the common central axis AA of the bone fixation member and the articulation member.

[0016] The first bore section of the bone fixation member has a cross-section extending perpendicularly to the central axis A of the bone fixation member, the cross-section of the first bore section defining a first polygonal outline.

[0017] The orientation pin has a cross-section defining a second polygonal contour line, such that when the articulation member with the orientation pin is seated in the inner bore of the bone fixation member, rotation of the articulation member in relation to the bone fixation member is prevented.

[0018] The prostheses for a joint in the hand or wrist as disclosed herein are especially useful when at least one implanted part of the prosthesis is provided with an asymmetric replacement articulation surface. Asymmetric replacement articulation surfaces in prostheses of a joint in the hand or wrist require precise alignment in relation to the opposing articulate surface, whether the opposing articulate surface is arranged on a native bone or on an opposing implant part of the prosthesis. Once the prosthesis is implanted, it is imperative that the precise alignment of its replacement articulation surface remains stable during normal use of the prosthesis.

[0019] The bone fixation member may have an exterior conical shape provided with outer threads, wherein the outer threads advantageously are self-tapping. The conical shape as well as self-tapping threads facilitate insertion of the bone fixation member into the bone.

[0020] The orientation pin may be provided at a first end of a shaft, wherein the shaft has an outer configuration adapted to be inserted into a second bore section of the inner bore of the bone fixation member. Advantageously, the shaft has a tapered configuration which allows for a press-fit interaction between the articulation member and the bone fixation member. The press-fit interaction further stabilizes the insertion of the articulation member into the bone fixation member.

[0021] The first and second bore sections of the inner bore are preferably centered, or substantially centered, along the central axis A of the bone fixation member. A centration of both the first and second bore sections around the central axis allows for a stable seating of the first part of the articulation member (i.e., the orientation pin on the shaft) along the central axis A inside the central bore. Thus, when the articulation member is inserted into the inner bore of the bone fixation member, a common central axis AA between the bone fixation member and the articulation member is formed that extends from the first end of the bone fixation member, through the first bore section and the orientation pin, the second bore section and the shaft, and to the second part with the replacement articulation surface.

[0022] The first polygonal outline may in one example be hexagonal. The second polygonal outline may in one example be dodecagonal. Both first and second polygonal outlines may in one example be similar. Both the first and second polygonal outlines may in one example be hexagonal. Both the first and second polygonal outlines may in one example be dodecagonal. In one example, the first polygonal outline may be hexagonal, and the second polygonal outline may be dodecagonal. The first and second polygonal outlines of the first bore section and the orientation pin respectively, allow for rotation of the articulation member in relation to the bone fixation member in small increments to enable a precise alignment of the replacement articulation surface in relation to its opposing articulation surface. Furthermore, once the alignment of the replacement and opposing articulation surfaces has been optimized, the first and second polygonal outlines of the first bore section and the orientation pin respectively, prevent rotation of the articulation member relative to the bone fixation member, thereby allowing for a stable implant that does not easily shift or become misaligned after implantation.

[0023] In some examples, the bone in the joint of the hand or wrist may be chosen from the group consisting of the proximal or distal carpal bones, the metacarpal bones, the proximal phalanx bones, the intermediate phalanx bones, or a forearm bone.

[0024] The replacement articular surface of the articulation member may be configured to interact with an opposing articular surface provided either by a bone in a joint of the hand or wrist, or an opposing implant part of a prosthetic device arranged in a bone in a joint of the hand or wrist.

[0025] The replacement articular surface may have different configurations depending on the configuration of the opposing articulation surface. The opposing articular surface may in some examples be proximal or distal carpal bones or a forearm bone. The opposing articular surface may in some examples be located on an opposing implant part configured to be inserted into a carpal bone, a metacarpal bone, a proximal phalanx bone, an intermediate phalanx bone, or a forearm bone. Some of the prostheses described herein may comprise a second implant part.

[0026] In some of the examples, there is provided a hemi radius prosthesis that may be configured to replace at least a part of the radiocarpal joint of the wrist. In some of these prostheses, the bone fixation member of the implant part is configured to be inserted into a radius bone in a radiocarpal joint.

[0027] In one of the examples wherein the bone fixation member of the implant part is configured to be inserted in the radius bone, the replacement articular surface of the articulation member may be configured to articulate with an opposing articular surface arranged on one or more distal carpal bones. In one example, the replacement articular surface is configured to articulate with the proximal end of capitate. This type of prosthesis provides a replacement of the radius side of the joint and enables a new articulation with the native capitate. The prosthesis may advantageously be used as a hemiarthroplasty of the wrist joint in cases with pain, malalignment or instability due to osteoarthritis, traumatic arthritis or rheumatoid arthritis. To provide an improved articulation with capitate, the replacement articulation surface of the prosthesis implant part is provided with a configuration that accommodates the articulating surface of capitate. Consequently, the replacement articulation surface has a configuration that is asymmetric about the common central axis AA formed when the articulation member is inserted into the bone fixation member. It is therefore crucial to the functioning of the implant that the alignment between the replacement articulation surface and capitate remains stable. The advantageous rotation- preventative arrangement described herein provides a durable and permanent implant that remains aligned and stable also after implantation.

[0028] In one of the examples wherein the bone fixation member of the implant part is configured to be inserted in the radius bone, the replacement articular surface of the articulation member is configured to articulate with an opposing articular surface arranged on one or more proximal carpal bones. In one example, the replacement articular surface is configured to articulate with the proximal ends of scaphoid and lunate. This type of prosthesis may advantageously be used as a hemiarthroplasty of the wrist joint when the distal end of the radius has been severely fractured but the proximal row of carpal bones is intact. The replacement articulation surface of the radius implant part is configured to articulate with the proximal ends of scaphoid and lunate. Consequently, the replacement articulation surface has a configuration that is asymmetric about the common central axis AA formed when the articulation member is inserted into the bone fixation member. It is therefore crucial to the functioning of the implant that the alignment between the replacement articulation surface and capitate remains intact and stable also after implantation of the prosthesis. The advantageous rotation-preventative arrangement described herein provides a durable and permanent implant.

[0029] In a further example, there is provided a prosthesis that is configured to replace the distal radioulnar joint between the radius and ulna. The prosthesis comprises an ulnar implant part with a bone fixation member configured to be inserted into an ulnar bone in a distal radioulnar joint. In this example the replacement articular surface is an ulnar replacement surface configured to engage with an ulnar notch on the radius bone in the distal radioulnar joint.

[0030] The distal radioulnar joint prosthesis is advantageous when the distal radioulnar joint needs to be replaced e.g., due to rheumatoid, degenerative, or post-traumatic arthritis presenting pain and weakness in the joint. The replacement articulation surface of the ulna implant part is configured to articulate with the ulnar notch provided on the radius bone and therefore presents an asymmetric configuration about the common central axis AA formed when the articulation member is inserted in the ulna bone fixation member. The important alignment between the replacement articulation surface and the ulnar notch on the radius bone is upheld also after implantation due to the rotation-preventative configuration provided by the prosthesis.

[0031] In a further example, there is provided a prosthesis that is configured to replace a radiocarpal joint between the radius bone and a proximal end of a metacarpal bone, i.e. , a wrist joint arthrodesis. The prosthesis comprises a first implant part and a second implant part, wherein the first implant part is configured to be inserted into the radius bone, and the second implant part is configured to be inserted into a proximal end of a metacarpal bone of the radiocarpal joint. The replacement articular surface of the first implant part is configured to engage with an opposing replacement articular surface arranged on the second implant part of the prosthesis. The first implant part of the prosthesis comprises a bone fixation member configured to be inserted into a distal end of the radius bone in the radiocarpal joint, and an articulation member with a replacement articular surface configured to articulate with an opposing replacement articular surface arranged on the opposing second implant part of the prosthesis. The second implant part of the prosthesis comprises a bone fixation member configured to be inserted into a proximal end of the metacarpal bone in the radiocarpal joint, and an articulation member with a replacement articular surface configured to articulate with an opposing replacement articular surface arranged on the opposing first implant part of the prosthesis. This wrist joint prosthesis has a radius cup with a center which is slightly offset from the central axis of the bone fixation member. This type of asymmetric wrist joint prosthesis is advantageous when e.g., the anatomy of the hand deviates from normal such that the symmetric alignment between the radius implant part and the metacarpal implant part in a normal wrist arthroplasty prosthesis is strained. The important alignment between the two replacement articulation surfaces (i.e. , the cup and the ball) is retained in the implant due to the rotation-preventative configuration provided by the prosthesis.

[0032] In a further example, there is provided a prosthesis that is configured to replace a carpometacarpal joint between distal carpal bone and a proximal end of a metacarpal bone, and more specifically a prosthesis that replaces the trapeziometacarpal joint between trapezium and the first metacarpus. The prosthesis comprises a first implant part and a second implant part, wherein the first implant part is configured to be inserted into a distal end of trapezium, and the second implant part is configured to be inserted into a proximal end of the first metacarpal bone of the trapeziometacarpal joint. The replacement articular surface of the first implant part is cup-shaped and configured to engage with a ball-shaped opposing replacement articular surface arranged on the second implant part of the prosthesis. The ball-shaped replacement articulation surface in the metacarpal implant part has an asymmetric configuration about the common central axis AA formed when the articulation member is inserted in the metacarpal bone fixation member, while the cup-shaped replacement articulation surface is symmetric about the common central axis AA formed when the cup-shaped articulation member is inserted in the trapezium bone fixation member.

[0033] The described prosthesis with an asymmetric configuration of the ball-shaped replacement articulation surface in the metacarpal implant part is necessary since a straight configuration (i.e., an axially symmetric alignment around the central axis in the metacarpal implant part) would cause strain and facilitate radial dislocation of the metacarpal ball from the cup. The important unstrained alignment between the two replacement articulation surfaces (i.e., the cup and the ball) is maintained in the implant due to the rotation-preventative configuration provided by the prosthesis.

[0034] In a further example, there is provided a prosthesis configured to replace a metacarpal phalangeal joint between a distal end of one of the metacarpal bones and a proximal end of one of the proximal phalanx bones. The metacarpal phalangeal joint prosthesis comprises a first implant part and a second implant part, wherein the first implant part is configured to be inserted into a distal end of a metacarpal bone, and the second implant part is configured to be inserted into a proximal end of a proximal phalanx bone of the metacarpal phalangeal joint. The replacement articular surface of the first implant part is configured to engage with an opposing replacement articular surface arranged on the second implant part of the prosthesis. The first implant part of the prosthesis comprises a bone fixation member configured to be inserted into the distal end of one of the second, third, fourth or fifth metacarpal bones of the metacarpal phalangeal joint, and an articulation member with a replacement articular surface configured to articulate with an opposing replacement articular surface arranged on the opposing second implant part of the prosthesis. The second implant part of the prosthesis comprises a bone fixation member configured to be inserted into the proximal end of one of the second, third, fourth or fifth proximal phalanx bones in the metacarpal phalangeal joint, and an articulation member with a replacement articular surface configured to articulate with an opposing replacement articular surface arranged on the opposing first implant part of the prosthesis. The metacarpal phalangeal joint prosthesis is advantageously used to replace the metacarpal phalangeal joint in a patient experiencing pain, malalignment or instability due to osteoarthritis, traumatic arthritis or rheumatoid arthritis in this joint. Both implant parts are provided with replacement articulation surfaces having asymmetric configurations about their common central axes AAa / AAb. Thus, the advantageous rotation-preventing features offered by the metacarpal phalangeal joint prosthesis are crucial in providing a safe and stable implant that will not dislocate after implantation.

[0035] In a further example, there is provided a prosthesis that may replace a proximal interphalangeal joint between a distal end of one of the proximal phalanx bones and a proximal end of one of the intermediate phalanx bones. The prosthesis comprises a first implant part and a second implant part, wherein the first implant part is configured to be inserted into a distal end of a proximal phalanx bone, and the second implant part is configured to be inserted into a proximal end of an intermediate phalanx bone of the proximal interphalangeal joint. The replacement articular surface of the first implant part is configured to engage with an opposing replacement articular surface arranged on the second implant part of the prosthesis. The first implant part of the prosthesis comprises a bone fixation member configured to be inserted into the distal end of one of the second, third, fourth or fifth proximal phalanx bones of the proximal interphalangeal joint, and an articulation member with a replacement articular surface configured to articulate with an opposing replacement articular surface arranged on the opposing second implant part of the prosthesis. The second implant part of the prosthesis comprises a bone fixation member configured to be inserted into the proximal end of one of the second, third, fourth or fifth intermediate phalanx bones in the proximal interphalangeal joint, and an articulation member with a replacement articular surface configured to articulate with an opposing replacement articular surface arranged on the opposing first implant part of the prosthesis. The proximal interphalangeal joint prosthesis is advantageously used to replace the proximal interphalangeal joint in a patient experiencing pain, malalignment or instability due to osteoarthritis, traumatic arthritis or rheumatoid arthritis in this joint. Both implant parts are provided with replacement articulation surfaces having asymmetric configurations about their common central axes AA. Thus, the advantageous rotationpreventing features offered by the proximal interphalangeal joint prosthesis is crucial in providing a safe and stable implant that will not dislocate after implantation.

[0036] BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Examples are described in more detail below with reference to the appended drawings. Fig. 1a illustrates the different joints in the hand and wrist.

[0038] Fig. 1b illustrates the different bones in the hand and wrist.

[0039] Figs 2a-o illustrate the principles of the prostheses described herein in relation to one example.

[0040] Figs 3a and b illustrate a prothesis in accordance with prior art.

[0041] Figs. 4a-e illustrate a further example of the prostheses described herein.

[0042] Figs. 5a-e illustrate a further example of the prostheses described herein.

[0043] Figs. 6a-e illustrate a further example of the prostheses described herein.

[0044] Figs. 7a-e illustrate a further example of the prostheses described herein.

[0045] Figs. 8a-h illustrate a further example of the prostheses described herein.

[0046] Figs. 9a-h illustrate a further example of the prostheses described herein.

[0047] Figs. 10a-c illustrate a further example of the prostheses described herein. Figs. 11a-c illustrate a further example of the prostheses described herein. Figs. 12a-f illustrate the wrist prosthesis modular system described herein Figs. 13a and b illustrate the screw tool used herein.

[0048] DETAILED DESCRIPTION

[0049] The detailed description set forth below provides information and examples of the disclosed prostheses with sufficient detail to enable those skilled in the art to practice the disclosure. One objective of the present disclosure is to provide improved prostheses for joints in the hand or wrist which enable an operator, e.g., an orthopedic surgeon, to optimize alignment of the prosthesis at the implantation site such that unhindered and stable articulation of the replaced joint is achieved also after implantation.

[0050] A further objective is to provide prostheses that form part of a modular prostheses system which allows easy conversion between different types of implants. The disclosed modular prostheses system offers salvage options that limit unnecessary implant removal by taking advantage of preexisting stable and osseointegrated implants. The disclosed modular prostheses system may provide easy conversion from e.g., a hemi radius prosthesis to a two-membered wrist joint implant with preserved wrist motion. Alternatively, the hemi radius prosthesis may be converted to a radiocarpal arthrodesis wherein the wrist joint is fused while preserving the bone available for arthrodesis by minimizing bone loss which would otherwise occur during removal of well-fixed implants.

[0051] When used herein, the terms “proximal” and “proximal end” are intended to mean a position in the hand or an end or segment of a bone in the hand located in a direction towards the elbow and shoulder of a patient, while the terms “distal” and “distally” are intended to mean a position in the hand or an end or segment of a bone in the hand located in a direction away from the elbow and shoulder towards the tips of the fingers of the patient.

[0052] Figs. 2a, 3a, 4a, 5a, 5a, 7a, 8a and c, 9a and c, 10a and 11a illustrate examples of prostheses configured for use in joints of the hand or wrist according to the present disclosure. Each prosthesis includes at least one bone fixation member and one articulation member (see e.g., Fig. 2c). However, some prostheses may have two bone fixation members and two articulation members, as seen in e.g., Figs. 3b and 3c.

[0053] When used herein, the expression “joint of the hand and wrist” is intended to include the following joints of the hand and wrist as seen in Fig. 1 a: the radiocarpal joint 41 , the radioulnar joint 42, the carpometacarpal joints 43-II, -III, -IV and -V including the trapeziometacarpal joint 43-I, the metacarpophalangeal joints 44- II, -III, -IV, and -V, and the proximal interphalangeal joints 45-II, -III, -IV, and -V. Not all joints listed above are eligible for the protheses described herein.

[0054] Depending on the joint, the bone fixation member(s) and articulation member(s) of the prostheses may be configured to be inserted into and / or interact with one or more of the following bones (see Fig. 1b): the distal end of either the radius 51 or ulnar 52 in the radiocarpal joint 41 or distal radioulnar joint 42; one of the proximal carpal bones; scaphoid 53a, lunate 53b, triquetrum 53c, and pisiform 53d; one of the distal carpal bones; trapezium 54a, trapezoid 54b, capitate 54c, and hamate 54d: the distal or proximal ends of one of the metacarpal bones 55-I, -II, -II, -IV and -V in the carpometacarpal joints 43-I, -II, -III, -IV and -V, or the metacarpophalangeal joints 44-I, -II, -III, -IV, and -V; the proximal or distal ends of the proximal phalanxes 56-I, -II, -II, -IV and -V in the metacarpophalangeal joints 44-I, -II, -III, -IV, and -V, or proximal interphalangeal joints 45-I, -II, -III, -IV, and -V; the proximal ends of one of the intermediate phalanxes 57-I, -II, -III, -IV, and -V in the proximal interphalangeal joints 45-I, -II, -III, -IV, and -V.

[0055] The general features of the prostheses of the invention will now be described in more detail in connection with Figs. 2a-o.

[0056] The prosthesis exemplified in Figs. 2a-o is a radius hemi prosthesis 100 configured to be implanted at the distal end of the radius 51 in the radiocarpal joint 41 and articulate with a proximal surface of capitate 54c as seen in Fig. 2a. A more detailed view of the radius hemi prosthesis 100 is illustrated in Fig. 2b. The radius hemi prosthesis 100 shown in Figs. 2a-o is used as an example to illustrate some general principles common to all prostheses 100, 200, 300, 400, 500, 600, 700, 800 and 900 described herein.

[0057] The prosthesis 100 disclosed in Figs. 2a-o comprises one bone fixation member 110 and one articulation member 120. The articulation member 120 is configured to be received in the bone fixation member 110 in a releasable manner, as seen in Fig. 2c. All prostheses disclosed herein comprise at least one bone fixation member and at least one articulation member.

[0058] The bone fixation member 110 is configured for being screwed into a first bone of a joint in the hand or wrist as listed above in connection with Figs.1a and 1b. However, for the radius hemi prosthesis 100 in Figs. 2a-o, the bone fixation member 110 is inserted in a distal end of the radius 51 at the radiocarpal joint 41 as seen in Fig. 2a.

[0059] The bone fixation member 110 has a cone-like outer configuration which tapers from a small diameter at its first end 111 towards a larger diameter at its second end 112 (see Fig. 2d). At least part of the outer surface 113 between the first and second ends 111, 112 of the bone fixation member 110 is advantageously provided with outer threads 114. The outer threads 114 facilitate screwing of the bone fixation member 110 into the bone, and the outer threads 114 of the conically shaped bone fixation member 110 engage into the cortical part of the bone. Advantageously the outer threads 114 are self-tapping such that they can tap their own hole as they are screwed into the bone after predrilling. However, in some variants of the bone fixation member, the outer threads may be replaced by a straight thread

[0060] The bone fixation member 110 comprises a central axis A which extends through the conically shaped bone fixation member 110 from its first end 111 to its second end 112, as seen in Fig. 2d. Since the bone fixation member 110 has a conical shape, the central axis A of the bone fixation member 110 is the straight line passing through the apex (i.e., the first end 111 of the bone fixation member 110), about which the base (i.e., the surface 115 at the second end 112) and the entire cone have a circular symmetry.

[0061] The bone fixation member 110 comprises an inner bore 116 which extends from the surface 115 at the second end 112 of the bone fixation member 110 towards the first end 111 but does not extend throughout the entire length of the bone fixation member 110. The inner bore 116 is centered or substantially centered along the central axis A of the bone fixation member 110 and is divided into two or more bore sections 117, 118 extending along the central axis A (see Fig. 2d).

[0062] The first bore section 117 is arranged towards the first end 111 of the bone fixation member 110 of the inner bore 116 and has an inner cross-section which preferably is constant throughout the length of the first bore section 117. The first bore section 117 of the inner bore 116 is configured to receive an orientation pin 123 arranged on the articulation member 120.

[0063] The articulation member 120 comprises a first portion 121 and a second portion 122 (see Fig. 2e). The first portion 121 is configured to connect the articulation member 120 to the bone fixation member 110, while the second portion 122 is provided with a replacement articular surface 130 configured for engagement, i.e., articulation, with an opposing articular surface, as will be explained in further detail below.

[0064] The first portion 121 of the articulation member 120 comprises the orientation pin 123 which is configured to be inserted into the first section 117 of the inner bore 116. The orientation pin 123 has a cross-section which is constant throughout its length. The cross- sectional size of the orientation pin 123 is the same, or substantially the same, as the inner cross-sectional size of the first bore section 117 in the bone fixation member 110. This allows for the first portion 121 of the articulation member, including 120 the orientation pin 123, to be seated inside the first bore section 117 of the inner bore 116 and be centered, or substantially centered, along the central axis A of the bone fixation member 110 with a snug fit.

[0065] Advantageously, orientation pin 123 is arranged at the end of a cone-shaped shaft 124 which tapers outwardly from the orientation pin 123 towards the second portion 122 of the articulation member 120. The inner bore 116 is provided with a second bore section 118 arranged between the first bore section 117 and the second end 112 of the bone fixation member 110. The second bore section 118 has an inner outline that corresponds to the tapered configuration of the shaft 124 such that when the articulation member 120 is inserted into the inner bore 116, it is retained therein by friction.

[0066] When the first portion 121 of the articulation member 120, i.e. , the shaft 124 with the orientation pin 123, is seated inside the first and second bore sections 117,118 of the inner bore 116, it is centered or substantially centered along the central axis A of the bone fixation member 110, such that the bone fixation member 110 and the articulation member 120 are aligned along a common central axis AA (see e.g., Fig. 2h).

[0067] The first bore section 117 of the inner bore 116 has an inner cross-section extending perpendicularly to the central axis A of the bone fixation member 116. The inner crosssection defines a first polygonal outline 119 (see Fig. 2i). The first polygonal outline 119 is advantageously adapted to permit a screw pin of a screw tool, e.g., a screwdriver, to be inserted therein to orient and secure the bone fixation member 110 by screwing the bone fixation member 110 into the respective bone.

[0068] An example of a screw tool 50 that may be used for inserting the bone fixation member into the bone is illustrated in Figs.13a-b. A handle 51 for gripping the screw tool 50 is provided at a first end of an elongated shaft 52, and a screw pin 53 is provided at the second end thereof. The screw pin 53 has a polygonal outline 59 configured to match the polygonal outline 119 of the first bore section 117 of the inner bore 116.

[0069] For example, if the first polygonal outline 119 of the first bore section 117 is hexagonal, the polygonal outline 59 of the screw pin 53 will be hexagonal (see Figs. 13a and b), If the first polygonal outline 119 of the first bore section 117 is dodecagonal, the polygonal outline 59 of the screw pin 53 will be dodecagonal (not shown).

[0070] Advantageously the shaft 52 of the screw tool 50 is fitted with an alignment template 55 configured to match the polygonal outline 59 of the screw pin 53. Thus, if the screw pin 53 has a hexagonal polygonal outline, the alignment template 55 on the shaft 22 also has a hexagonal outline wherein each side of the hexagonal shape coincides with each side of the hexagonal-shaped screw pin 53. The exact match between the alignment template 55 and the screw pin 53 enables the surgeon to precisely determine the rotational position of the bone fixation member 110 when inserting it into the bone.

[0071] The orientation pin 123 on the articulation member 120 has an outer cross-section extending perpendicular to the length of the orientation pin 123 defining a second polygonal outline 129 (see Fig. 2j), such that when the articulation member 120 with the orientation pin 123 is seated in the first bore section 117 of the bone fixation member 110, rotation of the articulation member 120 in relation to the bone fixation member 110 is prevented.

[0072] For example, in one example the first polygonal outline 119 may be hexagonal, and the second polygonalpolygonal outline 129 may be dodecagonal, as seen in Fig. 2I). This means that

[0073] - the polygonal outline 119 of the first bore section 117 in the inner bore 116 when viewed along the central axis A has a hexagonal shape (i.e., the inner periphery of the first bore section 117 has six inner side walls); and that

[0074] - the outer cross-section 129 of the orientation pin 123 when viewed at an angle parallel to the length of the orientation pin 123 has a dodecagonal shape (i.e., the outer periphery of the orientation pin 123 has twelve outer walls or edges).

[0075] In this example, the orientation pin 123 with its dodecagonal outline can be inserted into the first bore section 117 of the inner bore 116 having a hexagonal outline in twelve different positions, wherein each position differs by 30° around the central axis A (see Fig. 2k). Since the inner size of the first bore section 117 of the inner bore 116 and the outer size of orientation pin 123 are the same, or substantially the same, the articulation member 120 with the orientation pin 123 cannot rotate in relation to the bone fixation member 110 when inserted therein, as shown in Fig. 2I).

[0076] In a different example, the first and second polygonal outlines 119, 129 may be similar (not shown). In one example the first and second polygonal outlines 119, 129 may both be hexagonal. In this case, an orientation pin 213 with a hexagonal outline can be inserted into the first bore section 117 also having a hexagonal outline in six different positions, wherein each position differs by 60° around the central axis A (not shown).

[0077] In a further example, the first and second polygonal outlines 119, 129 may both be octagonal. In this example an orientation pin 123 with an octagonal outline can be inserted into the first bore section 117 also having an octagonal outline in eight different positions, wherein each position differs by 45° around the central axis A (not shown).

[0078] In still a further example the first and second polygonal outlines 119, 129 may both be dodecagonal. In this case an orientation pin 123 with a dodecagonal outline can be inserted into the first bore section 117 also having a dodecagonal outline, in twelve different positions, wherein each position differs by 30° around the central axis A (not shown).

[0079] Providing the orientation pin 123 of the articulation member 120 and the first bore section 117 of the inner bore 116 with first and second polygonal outlines 119, 129 respectively, may allow the orientation of the articulation member 120 in relation to the bone fixation member 110 to be more precise. When inserted into the inner bore 116, the articulation member 120 may be rotated around the central axis A in increments of e.g., 30°, 45° or 60° to fine tune the precise orientation of the articulation member 120 in the bone fixation member 110.

[0080] A further advantage is that when the orientation pin 123, which is arranged at the end of the articulation member 120, has been inserted into the first bore section 117 of the inner bore 116, the articulation member 120 is entirely prevented from rotating in relation to the bone fixation member 110.

[0081] The second portion 122 of the articulation member 120 comprises a “replacement articular surface” 130 configured for engagement with an opposing articular surface. When used herein, the terms “articulating surface”, “articulation surface” or “articular surface” are intended to mean a surface configured to have a shape adapted to define the motions required by a joint. In anatomy, the articulating surface is where the end of a bone meets another bone at a joint, and articular surfaces of the two bones are adapted to allow for different degrees or types of movement at the particular joint. For example, the articular surface of one bone may be concave, and the articular surface of the opposing bone is convex.

[0082] Prostheses configured for replacing, or partially replacing, a joint comprise “replacement” articular surfaces” which are configured to be a substitute for a natural articular surface of the joint. The replacement articulation surface of a joint prosthesis may be configured to engage an opposing articular surface arranged on a natural bone of the joint. An example of such a prosthesis is a radius hemi prosthesis 100, as illustrated in Figs. 2a-o herein, wherein the replacement articular surface 130 of the prosthesis 100 has a concave configuration that articulates to the convex articulation surface of the capitate 54c in the distal row of carpal bones.

[0083] Alternatively, the replacement articular surface may engage an “opposing replacement articular surface” of an opposing prosthesis implant part. An example of such a replacement articular surface is a wrist joint prosthesis 400, as shown in Figs. 6a-f explained further below, wherein the replacement articular surface 430a of a first prosthesis part 405a has the shape of a cup forming a socket to receive a replacement articular surface 430b shaped as a ball arranged on a second prosthesis part 405b. Thus, in a prosthesis comprised of two implant parts, the two replacement articular surfaces (e.g., the cup 430a and the ball 430b as in the prosthesis 400 of Fig. 6b) form two opposing articular surfaces configured for articulating the joint replaced by a prosthesis.

[0084] In view of this, the three-dimensional configuration of the replacement articular surface of the prostheses described herein may therefore vary substantially depending on the type of opposing articular surface in the joint it is intended to engage and articulate. As explained above, the opposing articular surface of the prosthesis may be a native bone, as in the prosthesis 100 of Figs. 2a-o, or it may be a second replacement articular surface arranged on an opposing implant part of the same prosthesis, as in the prosthesis 400 of Fig. 6a.

[0085] During normal use, i.e., when the prostheses described herein are implanted into joints of the hand or wrist, the articulation member with the orientation pin (regardless of its replacement articular surface) will be seated into the first bore section of the inner bore in the bone fixation member. As explained above, the advantageous first and second polygonal outlines of the first bore section in the inner bore and the orientation pin allows for precise orientation of the articulation member in relation to the bone fixation member during the implantation procedure, while it at the same time prevents any rotation of the articulation member in relation to the bone fixation member when the prosthesis has been implanted.

[0086] The relative orientation between the articulation member and the bone fixation member may not make a difference in all hand and wrist joint prostheses. For example, Figs. 3 a-b illustrate a wrist joint prosthesis 1 known in the art comprising two parts: a radius implant part 5a and a metacarpal implant part 5b. The radius implant part 5a comprises a radius bone fixation member 10a and an articulation member 20a provided with a radius cup articulation surface 30a. The radius implant part 5a is configured to be implanted into the cortical bone at the distal end of the radius bone 51. The metacarpal implant part 5b comprises a metacarpal bone fixation member 10b and an articulation member 20b provided with a metacarpal head articulation surface 30b. The metacarpal implant part 5b is configured to be inserted through capitate 54c and into the cancellous and cortical bone of the third metacarpus 55-III. When both prostheses parts 5a, 5b are inserted in the radius 51 and third metacarpus 55-III respectively, their replacement articular surfaces 30a, 30b provide a ball and socket articulation with a center of rotation very close to the anatomical center point in the native radiocarpal joint 41.

[0087] As seen in Figs. 3a-b the replacement articulation surfaces 30a, 30b of both prosthesis parts 5a, 5b (i.e. , the radius cup in the radius implant part 5a and the metacarpal sphere in the metacarpal implant part 5b) have a symmetric configuration about their common central axes AA when their articulation members 20a, 20b are inserted into their respective bone fixation elements 10a, 10b.

[0088] With the expression “having configuration that is axially symmetric around a common central axis” it is intended to mean that the replacement articular surface is axially symmetric if its appearance remains unchanged when it is rotated by any angle about the line passing lengthwise through its center. In this context “its cente is the common central axis AA formed when the articulation member with its orientation pin is seated inside the first bore section of the bone fixation member.

[0089] For instance, if the articulation member 20a with the symmetric radius cup 30a is rotated 30° in relation to the radius bone fixation member 10a, this will not impact its interaction with the metacarpal head articular surface 30b. Since the concave shape of the radius cup 30a (i.e., the replacement articular surface) is completely symmetric around the common central axis AA of the radius implant part 5a (i.e., the articulation member 20a when inserted into the bone fixation member 10a), it makes no difference how the articulation member 20a is rotated when inserted in the radius bone fixation member 10a. It will still articulate with the metacarpal head articular surface 30b of the metacarpal implant part 5b in a perfect manner. The same applies to the metacarpal head articular surface 30b since it also has a symmetric configuration about the common central axis AA formed when the metacarpal articulation member 20b is inserted into the metacarpal bone fixation member 10b.

[0090] However, there are several types of prostheses wherein the precise alignment of the articulation member is very important for the interaction of its replacement articulation surface with the opposing articular surface in the joint. This applies regardless of whether it is an opposing articular surface arranged on a natural bone of the joint, or an opposing replacement articular surface of a second implant part of the prosthesis.

[0091] The radius hemi prosthesis 100 illustrated in Figs. 2a-o and discussed above is one example of a prosthesis with a design configured to replace the radius side of the radial portion of the wrist joint (the scaphoid and lunate fossa). The radius hemi prosthesis 100 is similar to the radius implant part 5a of the wrist joint implant 10 as seen in Figs. 3a-b in that it also comprises a first implant part 105 comprising a radius bone fixation member 110 and an articulation member 120 provided with a cup-shaped replacement articulation surface 130. The radius hemi prothesis 100 is also configured to be implanted into the cortical bone at the distal end of the radius bone 51. However, the radius cup articular surface 130 in the radius hemi prosthesis 100 illustrated in Figs. 2a-o is configured to articulate with native capitate 54c in the distal row of the carpal bones. To optimize the articulation with capitate 54c, the replacement articulation surface 130 (i.e. , the radius cup) has a configuration tailored to interact with the proximal surface of capitate 54c (see Figs. 2a-c).

[0092] Fig. 2k is a perspective view of the radius hemi prosthesis 100, wherein it is seen that the cup-shaped articulation surface 130 of its articulation member 120 has a configuration that is axially asymmetric about the common central axis AA when the articulation member 120 with its orientation pin 123 is seated inside the inner bore of the radius bone fixation member 110 (see e.g., Figs. 2I).

[0093] Figs. 2m-o illustrate that the cup-shaped articular surface 130 has a three-dimensional configuration that extends in three directions x, y and z, such that the replacement articular surface 130 has a configuration wherein a first direction x extends along the common central axis AA formed when the articulation member 120 is inserted into the bone fixation member 110. A second direction y extends perpendicular to the first extension x, and a third direction z extends perpendicular to the first extension x and second extension y, such that the cup-shaped articular surface 130 has an extension in the yz-plane that is asymmetric about the common central axis AA formed when the articulation member 120 is inserted into the radius bone fixation member 110 (see Fig. 2o).

[0094] Since the concave shape of the cup-shaped articular surface 130 is asymmetric around the common central axis AA of the radius implant, it will make a difference how the articulation member 120 is aligned when inserted in the radius bone fixation member 110. The cup-shaped articulation surface 130 will only articulate correctly with the proximal surface of capitate 54c when the two articular surfaces 130, 54c are essentially perfectly aligned. This means that if the articulation member 120 with the cup-shaped articulation surface 130 is rotated a few degrees in either the clockwise or counterclockwise direction relative to the radius bone fixation member 110, this may impact its interaction with the articular surface of capitate 54c.

[0095] Furthermore, since perfect alignment of the two articulation surfaces (i.e., capitate 54c with the cup-shaped articulation surface 130) is required for proper functioning of the radiocarpal joint 41 , it is important that this alignment is not shifted after implantation of the prosthesis 100. A slight rotational shift of the articulation member 120 in relation to the radius bone fixation member 110 may cause painful friction at the articulating joint and, in a worst-case scenario, a loosening of the prosthesis 100.

[0096] As described above in connection with Fig. 2I, the inner cross-section of the bone fixation member inner bore 116 is provided with a first polygonal outline 119, e.g., a hexagonal outline, while the orientation pin 123 of the articulation member 120 has a cross-section with a second polygonal outline 129, e.g., a dodecagonal outline. To optimize the articulation between the cup-shaped articulation surface 130 of the hemi radius implant 100 and the native capitate 54c, the radius bone fixation member 110 is inserted into the distal end of the radius 51 by means of the screw tool 50 as described above.

[0097] As explained above, the screw tool 50 is advantageously provided with an alignment template 55 that mimics the first polygonal outline 119 of the first bore section 117 in the inner bore 116. The markings allow the surgeon to orient the bone fixation member 110 in an optimal position in the radius bone 51 , such that an optimal alignment of the cupshaped articulation surface 130 may be achieved when the articulation member 120 is inserted into the inner bore 116 of the bone fixation member 110.

[0098] The movement of the joint, i.e., in the case of the hemi radius prosthesis 100 in Figs. 2a- o, is continuously tested throughout the implantation procedure. If the alignment between the articulating surfaces 130, 54c (i.e., the asymmetric cup and the native capitate 54c) is not perfect, the articulation member 120 may be removed (i.e., the orientation pin 123 of the articulation member 120 is disengaged from the first bore section 117 of the inner bore 116), rotated 30° either in the clockwise or counter-clockwise direction, and thereafter reinserted into the hexagonal-shaped first bore section 117. This may be repeated until optimal alignment between the replacement articulation surface 130 and capitate 54c is achieved. Alternatively, or to further optimize the fit, the bone fixation member 110 may also be rotated slightly in either direction inside the radius bone 51 by means of the screw tool 50.

[0099] Once the perfect orientation of the replacement articulation surface 130 in relation to capitate 54c has been determined, and the orientation pin 123 is finally correctly inserted in the first bore section 117 of the inner bore 116, there will be no further risk of the articulation member 120 rotating in relation to the bone fixation member 110. The first and second polygonal outlines 119, 129 and the snug fit between the first bore section 117 of the inner bore 116 and the orientation pin 123 prevent any relative rotation between the two members.

[0100] Figs. 4a-e disclose a variant of the radius hemi prosthesis 100 described in Figs. 2a-o, which may advantageously be used when the distal end of the radius 51 has been severely fractured but the proximal row of carpal bones is intact. This trauma / fracture hemi radius prosthesis variant 200 is provided with a cup-shaped replacement articular surface 230 configured to articulate with an opposing articular surface arranged on one or more bones in the proximal row of carpal bones.

[0101] As seen in Fig. 4a, a fractured part at the distal end of the radius has been removed, such that the bone fixation member 210 may be inserted further down into the radius bone 51. Figs. 4b and 4e disclose that the replacement articular surface 230 has a shape that is different from the cup-shaped articular surface 130 in the radius hemi prosthesis 100 disclosed in Figs. 2a-o. The hemi radius prosthesis variant 200 is configured to articulate with scaphoid 53a and lunate 53b in the proximal row of carpals.

[0102] In a manner similar to the radius hemi prosthesis 100, the hemi radius prosthesis variant 200 also has a replacement articulation surface 230 with a configuration that is axially asymmetric about the common central axis AA when the articulation member 220 with its orientation pin 223 is seated inside the first bore section 217 in the radius bone fixation member 210. Fig. 4e illustrates that the cup-shaped articular surface 230 has an extension in the y,z-plane that is asymmetric about the common central axis AA formed when the articulation member 220 is inserted into the radius bone fixation member 210 (see Figs. 4b and c).

[0103] It is therefore important that the articulation member 220 is properly aligned inside the bone fixation member 210, and that it is prevented from rotating in relation to the radius bone fixation member 210 to avoid malfunction of the prosthesis 200 once it has been implanted in the radius 51. Alignment of the cup-shaped articulation surface 230 of the trauma / fracture hemi prosthesis to scaphoid 53a and lunate 53b is achieved by screwing the radius bone fixation member 210 into the distal end of the radius 51 , by means of the screw tool 50 as described above for the radius hemi prosthesis 100. Advantageously the first polygonal outline 219 of the first bore section 217 in the inner bore 216 is hexagonal, and markings on the screw tool 50 are used to orient the bone fixation member 210 in the radius 51. However, the first bore section 217 may in some examples as described above have an octagonal, dodecagonal or other type of polygonal outline.

[0104] As seen in Fig. 4d, the cross-sectional outer contour of the orientation pin 223 on the articulation member 220 is provided with a second polygonal outline 229.

[0105] Advantageously, the second polygonal outline 229 is dodecagonal. However, it may, as described above, also have an octagonal, hexagonal or other type of polygonal outline. The articulation member 220 is oriented such that its cup-shaped articulation surface 230 engages scaphoid 53a and lunate 53b, and thereafter it is inserted into the inner bore 216 of the radius bone fixation member 210.

[0106] If not perfectly aligned, the articulation member 220 may be removed, rotated 30°in the direction as required, and then reinserted in the inner bore 216 as described above for the radius hemi prosthesis 100. If further fine tuning of the alignment is required, the radius bone fixation member 210 may also be rotated slightly using the screw tool 50 to improve the fit, as described for the radius hemi prosthesis 100 above. Once the dodecagonalshaped orientation pin 223 is correctly fitted inside the hexagonal-shaped first bore section 217 of the inner bore 116, rotation between the articulation member 220 and the bone fixation member 210 is permanently prevented.

[0107] Still a further example of the prostheses described herein is configured to partially replace the distal part of ulna in the distal radioulnar joint (DRU) 42, as illustrated in Figs. 5a-e. Fig. 5a illustrates a partial ulnar head implant 300 located in the DRU 42. Fig 5b is a detailed view of the partial ulnar head implant 300 of Fig 5a.

[0108] The partial ulnar head implant 300 comprises an ulnar bone fixation member 310 and an ulna articulation member 320 provided with an ulnar replacement articulating surface 330. The ulnar bone fixation member 310 is configured to be inserted into a distal end of the ulnar 52. When implanted, the ulnar replacement articulating surface 330 will articulate with the sigmoid notch 60 (also referred to the ulnar notch or sigmoid cavity) on the distal end of the radius 51. Figs. 5c-e illustrate that the ulnar replacement articulating surface 330 has a configuration that is axially asymmetric about the common central axis AA when the ulnar head articulation member 320 is seated inside the first bore section 317 in the ulnar bone fixation member 310. Fig. 5d illustrates that the ulnar replacement articulating surface 330 has an extension in the yz-plane that is asymmetric about the common central axis AA formed when the articulation member 320 is inserted into the ulnar bone fixation member 310.

[0109] For this reason, it is important that the ulnar head articulation member 320 is properly aligned inside the ulnar bone fixation member 310, and that it is prevented from rotating in relation to the ulnar bone fixation member 310 to avoid malfunction of the prosthesis 300 once it has been implanted in the ulnar 52.

[0110] Alignment of the ulnar replacement articulating surface 330 to the sigmoid notch 60 on the radius 51 is achieved by screwing the ulnar bone fixation member 310 into the distal end of the ulnar bone 52, by means of the screw tool 50 as described above e.g., for the radius hemi prosthesis 100. Advantageously, the first polygonal outline 319 of the first bore section 317 in the inner bore 316 is hexagonal, and markings on the screw tool are used to orient the ulnar bone fixation member 310 in the ulnar 52. However, the first bore section 317 may in some examples as described above, have an octagonal, dodecagonal or other type of polygonal outline.

[0111] As seen in Fig. 5b, the cross-sectional outer contour of the orientation pin 323 on the ulnar head articulation member 320 is provided with a second polygonal outline 329. Advantageously, the second polygonal outline 329 is dodecagonal. However, it may, as described above, also have an octagonal, hexagonal or other type of polygonal outline. The ulnar head articulation member 320 is oriented such that its ulnar replacement articulating surface 330 engages the sigmoid notch 60 at the distal end of the radius 51 , and thereafter it is inserted into the first bore section 317 of the inner bore 316 in the radius bone fixation member 310.

[0112] If not perfectly aligned, the ulnar head articulation member 320 may be removed, rotated 30° in a direction as required, and then reinserted into the inner bore 316 as described above for e.g., the radius hemi prosthesis 100. If further fine tuning of the alignment is required, the ulnar bone fixation member 310 may also be rotated slightly using the screw tool 50 to improve the fit, as described for the radius hemi prosthesis 100 above. Once the dodecagonal-shaped orientation pin 323 is correctly fitted inside the hexagonal-shaped first bore section 317 of the inner bore 316, rotation between the ulnar head articulation member 320 and the ulnar bone fixation member 310 is permanently prevented.

[0113] Figs. 6a-f disclose an asymmetric wrist joint arthrodesis 400 that is similar to the wrist joint prosthesis 1 disclosed in Figs. 3a-b, in that it comprises two opposing implant parts: a radius implant part 405a and a metacarpal implant part 405b configured to replace the wrist joint between the radius and the third metacarpus 55-III. The asymmetric wrist joint prosthesis 400 is advantageously used if there is an anatomic deviation such that the bone fixation members 10a and 10b in the wrist prosthesis 1 in Figs. 3a-b are not perfectly aligned with one another.

[0114] The radius implant part 405a of the asymmetric wrist prosthesis 400 comprises a radius bone fixation member 410a and a radius articulation member 420a provided with an asymmetrically cup-shaped replacement articulation surface 430a. The radius implant part 405a is configured to be implanted into the cortical bone at the distal end of the radius 51.

[0115] The metacarpal implant part 405b of the asymmetric wrist prosthesis 400 comprises a metacarpal bone fixation member 410b and a metacarpal articulation member 420b provided with a ball-shaped replacement articulation surface 430b. The metacarpal implant part 405b is configured to be inserted through capitate 54c and into the cancellous and cortical bone of the third metacarpus 55-III. When both prosthesis parts 405a, 405b are inserted in the radius 51 and third metacarpus 55-III respectively, their replacement articulation surfaces 430a, 430b provide a ball and socket articulation with a center of rotation very close to the anatomical center point of rotation in the native wrist joint.

[0116] However, in contrast to the wrist joint prosthesis 1 disclosed in Figs. 3a-b, the replacement articulation surface 430a of the radius articulation member 420a in Figs. 6a-f (i.e. , the radius cup in the radius implant part 405a) has an asymmetric configuration about the common central axis AAa formed when the radius articulation member 420a of the radius implant part 405a is inserted into the radius bone fixation member 410a (see especially Fig. 6f). The cup-shaped articular surface 430a has an extension in the yz- plane that is asymmetric about the common central axis AAa formed when the radius articulation member 420a is inserted into the radius bone fixation member 410a (see Figs. 6e and f).

[0117] Since the cup-shaped articular surface 430a of the radius articulation member 420a in the radius implant part 405a has a configuration that is axially asymmetric about the common central axis AAa when the articulation member 420a is inserted in the radius bone fixation member 410a, the radius articulation member 420a requires proper alignment in the radius bone fixation member 410a to ensure proper functioning of the wrist joint prosthesis 400.

[0118] The opposing replacement articular surface 430b, i.e., the metacarpal head of the metacarpal articular member 420b is, however, completely symmetrical about the common central axis AAb formed in the metacarpal implant part 405b (see Fig. 6d and f). Consequently, the ball-shaped metacarpal articular member 420b does not require a precise rotational alignment when inserted into its bone fixation member 410b. As a matter of fact, the metacarpal articulation member 420b may be allowed to rotate freely in relation to the metacarpal bone fixation member 410b also after implantation. Rotation of the metacarpal articulation member 420b with the symmetric replacement articulation member 430b (i.e., the ball shaped metacarpal head) will not affect its alignment with the opposing replacement articulation surface 430a (i.e., the off-set radius cup). It is therefore not necessary to provide the metacarpal articulation member 420b with an orientation pin 423b having a second polygonal outline 429b that will prevent its rotation in relation to the metacarpal bone fixation member 410b.

[0119] Instead, it may be sufficient that the first portion 421b of the metacarpal articulation member 420b is provided with a conical configuration (see Fig. 6f) which tapers from a wide diameter towards a smaller diameter that corresponds to the tapered configuration provided in the second bore section 418 of the inner bore 418. When the metacarpal articulation member 420b is inserted into the inner bore 416, it is retained therein by friction.

[0120] However, in an alternative example of the asymmetric wrist prosthesis 400, the cupshaped articulation surface may have a symmetric configuration about the common central axis AAa formed when the radius articulation member of the radius implant part is inserted into the radius bone fixation member (not shown). In this example, the ballshaped articulation surface may instead have an asymmetric configuration about the common central axis AAb formed when the metacarpal articulation member of the metacarpal implant part is inserted into the metacarpal bone fixation member. In this variant it is therefore important that the metacarpal implant part 405b of the wrist joint prosthesis 400 is provided with rotation-preventive measures, as described herein

[0121] Thus, also the metacarpal bone fixation member is advantageously provided with an inner bore section having a first polygonal outline (preferably a hexagonal outline), and the metacarpal articulation member of the metacarpal implant part is provided with an orientation pin having a second polygonal outline, preferably a dodecagonal outline. During implantation, the two bone fixation members 420a, 420b of the metacarpal implant part 405b and the radius implant part 405a are advantageously first inserted in the radius 51 and metacarpal bone 55-III respectively.

[0122] The radius bone fixation member 410a is positioned into cancellous and cortical bone of the distal end of the radius by means of the screw tool 50, as described above for e.g., the radius bone fixation member 110 in the radius hemi prosthesis 100. Advantageously, the first polygonal outline 419a of the first bore section 417a in the inner bore 416a is hexagonal.

[0123] The metacarpal bone fixation member 410b is inserted into the cancellous and cortical bone at the proximal end of the metacarpus 55-III by means of a screw tool 50, as described above e.g., in connection with the radius bone fixation member 110 in the radius hemi prosthesis 100.

[0124] This type of asymmetric wrist joint prosthesis as described herein, wherein the center of the radius cup is slightly offset to the central axis of the bone fixation member, is advantageous when e.g., the anatomy of the hand deviates from normal such that the symmetric alignment between the radius implant part 5a and the metacarpal implant part 5b in the normal wrist prosthesis 1 in Figs. 3a-b, is strained.

[0125] During the implantation procedure, and after both bone fixation members 420a, 420b have been inserted in metacarpus 55-III and radius respectively, the surgeon will use trials to determine the optimal movement of the wrist joint. If it turns out that the alignment between the radius implant part and the metacarpal implant part is strained due to e.g., an anatomic deviation in the joint of the patient, the surgeon may choose to insert the radius articulation member 420a provided with an asymmetric cup-shaped replacement articular surface 430a instead of the regular symmetrical cup 30a, as seen in Figs. 3a-b.

[0126] Alignment of the trial off-set cup replacement articular surface 430b to the opposing trial ball-shaped metacarpal head articular surface 430b is achieved as follows: A trial metacarpal articulation member 420b is inserted into the inner bore 416b of the metacarpal bone fixation member 410b.

[0127] Thereafter, the trial radius articulation member 420a with the off-set cup articulation surface 430a is aligned such that the off-set radius cup articulates with the metacarpal ball-shaped articulation surface 430b on the metacarpal implant trial part 405b in an unconstrained manner. If the alignment between the two trial replacement articulation surfaces 430a, 430b requires further fine tuning, the off-set cup shaped articulation trial member 430a may be removed, rotated 30°in either of two directions, and thereafter reinserted into the inner bore 416a.

[0128] Alternatively, the radius bone fixation member 410a may also be rotated slightly using the screw tool 50 to improve the fit, as described for the radius hemi prosthesis 100 above. Once the two opposing trial replacement articulation surfaces 430a, 430b are properly aligned, and optimal movement of the wrist joint has been attained, the two trials are replaced with the actual implants (i.e., the radius articulation member 420a and the metacarpal articulation member 420b).

[0129] Once the dodecagonal-shaped orientation pin 423a is properly oriented inside the hexagonal-shaped inner bore 416a of the radius bone fixation member 410a, rotation between the radius articulation member 420a and the radius bone fixation member 410a in the radius implant part 405a is permanently prevented.

[0130] By replacing the radius articulation member 20a having a symmetrically shaped cup for a radius articulation member 420a with an asymmetric cup-shaped replacement articular surface 430a as provided by the in the asymmetric wrist prosthesis 400, the painful strain between the implantation parts may be relieved.

[0131] Figs. 7a-f illustrate a further variant of the prostheses described herein, which is a trapeziometacarpal joint prosthesis 500 configured to replace the carpometacarpal joint 43-I between the first metacarpus 55-I and the distal end of the trapezium carpal bone 54a (see Fig. 7a).

[0132] The trapeziometacarpal joint prosthesis 500 comprises a trapezium implant part 505a configured to be implanted into the distal end of trapezium 54a, and a metacarpal implant part 505b configured to be implanted into the proximal end of the first metacarpal bone 55-I (see Figs. 7a and b).

[0133] The trapezium implant part 505a in Figs. 7a-f comprises a trapezium bone fixation member 510a and a trapezium articulation member 520a provided with a cup-shaped replacement articulation surface 530a. The trapezium bone fixation member 505a is shorter than the bone fixation members discussed above since it is inserted into a distal end of trapezium 54a which is much shorter than e.g., the radius or metacarpal bones into which the bone fixation members have been inserted above. In some examples, the trapezium bone fixation member 510a lacks outer threads and is fitted into the trapezium bone 54c in a press fit manner (not shown). The metacarpal implant part 505b comprises a metacarpal bone fixation member 510b and a metacarpal articulation member 520b provided with a ball-shaped replacement articulation surface 530b. When both prosthesis implant parts 505a, 505b are inserted in the trapezium 54a and first metacarpus 55-I respectively, their replacement articulation surfaces 530a, 530b provide a ball and socket articulation with a center of rotation very close to the anatomical center point of rotation in a native trapeziometacarpal joint 43-I.

[0134] From Figs 7b-f it is seen that the cup-shaped replacement articulation surface 530a provided on the trapezium implant part 505a has a configuration that is axially symmetric around a common central axis AAa formed in the trapezium implant part 505a, when the trapezium articulation member 520a is inserted into the trapezium bone fixation member 510a. Thus, rotational alignment of the trapezium articulation member 520a in relation to the trapezium bone fixation member 510a is of little importance once the trapezium implant part 505a has been implanted in the trapeziometacarpal joint 43-I. In view of this, the trapezium articulation member 520a is not provided with an orientation pin and is engaged in the trapezium bone fixation member 510a by means of a press fit in the second bore section of the bone fixation bore.

[0135] However, the ball-shaped replacement articulation surface 530b of the metacarpal articulation member 520b has a configuration that is axially asymmetric around a common central axis AAb formed in the metacarpal implant part 505b (see especially Fig. 7f). The ball-shaped articular surface 530b has an extension in the yz-plane that is asymmetric about the common central axis AAb formed when the metacarpal articulation member 520b has been inserted in the metacarpal bone fixation member 510b (see Figs. 7c, e and f).

[0136] Thus, in order to articulate properly with the opposing replacement articulating surface 530a (i.e., the cup-shaped articulating surface) provided on the opposing trapezium implant part 505a, the metacarpal articulation member 520b must be carefully oriented inside the metacarpal bone fixation member 510b during the implantation procedure. It is further imperative that the metacarpal articulation member 510b is prevented from rotating in relation to the metacarpal bone fixation member 510b to avoid malfunction of the trapeziometacarpal joint prosthesis 500 once it has been implanted in the trapeziometacarpal joint 43-I.

[0137] The asymmetric configuration of the ball-shaped replacement articulation surface 530b in the metacarpal implant part 505b is necessary since a straight configuration (i.e., an axially symmetric alignment around the central axis AAb in the metacarpal implant part 505b) would cause strain and facilitate radial dislocation of the metacarpal ball from the cup.

[0138] Alignment of the ball-shaped articulation surface 530b of the metacarpal implant part 505b to the cup-shaped articulation surface 530a on the trapezium implant part 505b is achieved as follows:

[0139] The metacarpal bone fixation member 510b is inserted into the proximal end of the first metacarpus 55-I, by means of the screw tool 50 as described above. Advantageously the first polygonal outline 519b of the inner bore 516b in the metacarpal bone fixation member 510b is hexagonal. However, the first polygonal outline 519b may, as described above, have an octagonal, dodecagonal or other type of polygonal outline.

[0140] As seen in Fig. 7b, the outer contour line of the orientation pin 523b on the metacarpal articulation member 520b is provided with a second polygonal outline 529b.

[0141] Advantageously, the second polygonal outline 529b is dodecagonal (although it may, as described above have an octagonal, hexagonal or other type of polygonal outline).

[0142] The metacarpal articulation surface 530b is aligned to the symmetric cup-shaped articulation surface 530a such that unhindered articulation is enabled between the two opposing articulation surfaces 530a, 530b. The metacarpal articulation member 520b with its ball-shaped articulation surface 530b is thereafter inserted into the inner bore 516b of the metacarpal bone fixation member 510b.

[0143] If not perfectly aligned, the metacarpal articulation member 520b may be removed in a manner as described above for the radius hemi prosthesis 100, rotated 30° in either a clockwise or counterclockwise direction, and then reinserted into the inner bore 516b. If further fine tuning of the alignment is required, the metacarpal bone fixation member 510b may also be rotated slightly in a required direction using the screw tool to improve the fit, in a manner as described for the radius hemi prosthesis 100 above. Once the trapeziometacarpal joint prosthesis 500 has been properly implanted, and the dodecagonal-shaped orientation pin 523b is finally fitted inside the hexagonal-shaped first bore section 517b of the inner bore 516b, rotation between the metacarpal articulation member 520b and the metacarpal bone fixation member 510b is permanently prevented.

[0144] A further example of the prostheses described herein is configured to replace a metacarpophalangeal joint 44-II, -III, -IV, or -V of the hand, as illustrated in Figs. 8a-h. Fig. 8a illustrates a metacarpophalangeal joint prosthesis 600 located in the metacarpophalangeal joint 44-III between the third metacarpus 55-III and the third proximal phalanx 56-111, while Fig. 8c illustrates the same metacarpophalangeal joint prosthesis 600 located in the metacarpophalangeal joint 44-11 between the fifth metacarpus 55-V and the fifth proximal phalanx 56-V. Fig. 8b is a detailed view of the metacarpophalangeal joint prosthesis 600 shown in Fig. 8a.

[0145] The metacarpophalangeal joint prosthesis 600 comprises two prosthesis parts: one metacarpal implant part 605a configured to be inserted into a distal end of a metacarpus 55-11, -III, -IV or -V, and one proximal phalanx implant part 605b configured to be inserted into a proximal end of a proximal phalanx 56-11, -III, -IV or -V (see e.g., Fig. 8a and 8e-1).

[0146] The metacarpal implant part 605a comprises a metacarpal bone fixation member 610a and a metacarpal articulation member 620a provided with a one-sided flange-shaped replacement articulation surface 630a. The proximal phalanx implant part 605b comprises a proximal phalanx bone fixation member 610b and a proximal phalanx articulation member 620b provided with an offset cup-shaped replacement articulation surface 630b. The one-sided flange-shaped articulation surface 630a of the metacarpal implant part 605a is configured to articulate with the offset cup-shaped replacement articulation surface 630b provided on the proximal phalanx implant part 605b when implanted in a metacarpophalangeal joint 44-II, -III, -IV, or -V.

[0147] Figs. 8d-1 and 8d-2 both disclose views of the same metacarpophalangeal joint prosthesis 600 but viewed from different angles. Fig. 8d-1 is an illustration of the metacarpophalangeal joint prosthesis 600 viewed from a first angle, and Fig. 8d-2 is a view of the same prosthesis when rotated 90° in the counterclockwise direction compared to the view in Fig. 8d-1. From Figs. 8c-h, it will be seen that both replacement articulating surfaces 630a, 630b of the metacarpophalangeal joint prosthesis 600 have configurations that are axially asymmetric around their common central axes AAa / AAb that are formed when their respective bone fixation members 610a, 610b and articulation members 620a, 620b are connected (see Figs. 8h-1 , 8h-2).

[0148] Figs. 8e-1 and 8e-2 disclose the different parts 605a, 605b of the metacarpophalangeal joint prosthesis 600 viewed from different angles to enable a clearer view of the asymmetry exhibited by the two articulation surfaces 630a, 630b.

[0149] Fig. 8e-1 discloses that the off-set cup-shaped replacement articular surface 630b of the proximal phalanx implant part 605b has an extension in the yz-plane that is asymmetric about the common central axis AAb formed when the proximal phalanx articulation member 620b is inserted into the proximal phalanx bone fixation member 610b (see also Fig. 8h-1). Fig. 8e-2 discloses that the one-sided flange-shaped replacement articular surface 630a of the metacarpal implant part 605a has an extension in the yz-plane that is asymmetric about the common central axis AAa formed when the metacarpal articulation member 620a is inserted into the metacarpal bone fixation member 610a (see also Fig. 8h-1).

[0150] Consequently, the replacement articulating surfaces 630a, 630b of both implant parts 605a, 605b in the metacarpophalangeal joint prosthesis 600 must be carefully aligned with each other during the implantation procedure.

[0151] To facilitate the alignment of the articulation members 620a, 620b in their respective bone fixation members 610a, 610b, the first bore sections 617a, 617b in the respective bone fixation members 610a, 610b are provided with inner cross-sections having a first polygonal outline 619a, 619b as for bone fixation members described above. Preferably, the first polygonal outline 619a, 619b of the first bore sections 617a, 617b in the metacarpal bone fixation member 610a, as well as the proximal phalanx bone fixation member 610b, have hexagonal shapes. Insertion and orientation of the metacarpal bone fixation member 610a and the proximal phalanx bone fixation member 610b into the distal end of the metacarpus 55-II, -III, -IV, or -V and the proximal end of the proximal phalanx 56-II, -III, -IV, or -V respectively, is achieved by means of a screw tool 50 as described above for e.g., the radius hemi prosthesis 100.

[0152] Each one of the orientation pins 623a, 623b provided on the metacarpal articulation member 620a and proximal phalanx member 620b respectively, has an outer crosssection with a second polygonal shape 629a, 629b. Preferably the second polygonal shapes of both orientation pins 623a, 623b are dodecagonal, but they may also have an octagonal, hexagonal (as seen in Figs. 8d-1 and 8d-2), or other types of outer polygonal outlines.

[0153] Alignment of the two opposing articulation surfaces 630a, 630b in their respective implant parts 605a, 605b is advantageously performed in stages.

[0154] In the first stage each bone fixation member 610a, 610b is inserted in the distal end of the metacarpus 55-II, -III, -IV, or -V and the proximal end of the proximal phalanx 56-II, -III, - IV, or -V respectively. Thereafter, trials of the articulation members 620a, 620b are inserted into their respective bone fixation members 610a, 610b with an aim for a general alignment of their articulation surfaces 630a, 630b such that the replacement articulation surfaces 630a,630bcan be expected to articulate in a reasonable manner with each other in the final implant 600. In the next stage, the final orientation of each articulation member 620a, 620b inside its bone fixation member 610a, 61 Ob may be aligned using the actual articulation member 620a, 620b in a manner already described in detail above. Alignment can be achieved by lifting the articulation member 620a, 620b such that its orientation pin 623a, 623b disengages the first bore section 617a, 617b of the inner bore 616a, 616b, rotating the articulation member 620a, 620b 30° in either a clockwise or counterclockwise direction, and reinserting the articulation member 620a, 620b with its orientation pin 623a, 623b into the first bore section 617a, 617b of the inner bore 616a, 616b. If further fine tuning of the alignment is required, the bone fixation member 610a, 610b may also be slightly rotated using the screw tool 50 to improve the fit. The last stage is repeated for both articulation members 620a, 620b until the optimal alignment of the one-sided flange-shaped replacement articular surface 630a with the off-set cup-shaped replacement articular surface 630b has been achieved in a manner such that unhindered articulation between the opposing replacement articular surfaces 630a, 630b is allowed.

[0155] Once the optimal alignment has been reached and the hexagonal-shaped orientation pins 623a, 623b of each articulation member 620a, 620b have been secured inside the hexagonal-shaped first bore sections 617a, 617b in the bone fixation members 610a, 610b, rotation between the articulation members 620a, 620b and their respective bone fixation members 610a, 610b is permanently prevented in the metacarpophalangeal joint prosthesis 600 when finally implanted.

[0156] Yet a further example of the prostheses described herein is configured to replace a proximal interphalangeal joint 45-II, -III, -IV, or -V of the hand as illustrated in Figs. 9a-h. Fig. 9a illustrates a proximal interphalangeal joint prosthesis 700 located in the proximal interphalangeal joint 45-III between the third proximal phalanx 56-III and the third intermediate phalanx 57-III, and Fig. 9c illustrates a proximal interphalangeal joint prosthesis 700 located in the proximal interphalangeal joint 45-V between the fifth proximal phalanx 56-V and the fifth intermediate phalanx 57-V. Fig. 9b is a detailed view of the proximal interphalangeal joint prosthesis 700 of Fig. 9a.

[0157] The proximal interphalangeal joint prosthesis 700 comprises two prosthesis parts: one proximal phalanx implant part 705a configured to be inserted into a distal end of a proximal phalanx 56-II, -III, -IV, or -V, and one distal phalanx implant part 705b configured to be inserted into a distal end of a distal phalanx 57-II, -III, -IV, or -V (see e.g., Figs. 9a and 9c). The proximal phalanx implant part 705a comprises a proximal phalanx bone fixation member 720a and a proximal phalanx articulation member 710a provided with a two-sided flange-shaped replacement articulation surface 730a. The intermediate phalanx implant part 705b comprises an intermediate phalanx bone fixation member 710b and an intermediate phalanx articulation member 720b provided with a partly partitioned cupshaped replacement articulation surface 730b (see e.g., Figs. 9e-1 and 9e-2).

[0158] The two-sided flange-shaped articulation surface 730a of the proximal phalanx implant part 705a is configured to articulate with the partially partitioned cup-shaped replacement articulation surface 730b provided on the intermediate phalanx implant part 705b when implanted in the proximal interphalangeal joint 45-II, -III, -IV, or -V.

[0159] Figs. 9d-1 and 9d-2 both disclose views of the same proximal interphalangeal joint prosthesis 700. Fig. 9d-1 is an illustration of the proximal interphalangeal joint prosthesis 700 viewed from a first angle, and Fig. 9d-2 is a view of the same prosthesis 700 when rotated 90° in the counterclockwise direction compared to the view in Fig. 9d-1. From Figs. 9a-h, it is seen that both articulating surfaces 730a, 730b of the proximal interphalangeal joint prosthesis 700 have configurations that are axially asymmetric around their common central axes AAa / AAb formed when their respective bone fixation members 710a, 710b and articulation members 720a, 720b are connected.

[0160] Figs. 9e-1 and 9e-2 are perspective views of the proximal interphalangeal joint prosthesis 700 seen from different angles to enable a clearer view of the asymmetry exhibited by the two replacement articulation surfaces 730a, 730b.

[0161] Fig. 9e-1 discloses that the partially partitioned cup-shaped replacement articular surface 730b of the distal phalanx implant part 705b has an extension in the yz-plane that is asymmetric about the common central axis AAb formed when the intermediate phalanx articulation member 720b is inserted into the intermediate phalanx bone fixation member 710b (see also Fig. 9f).

[0162] Fig. 9e-2 discloses that the two-sided flange-shaped replacement articular surface 730a of the proximal phalanx implant part 705a has an extension in the yz-plane that is asymmetric about the common central axis AAa formed when the proximal phalanx articulation member 720a is inserted into the proximal phalanx bone fixation member 710a (see also Fig. 9g).

[0163] Consequently, the replacement articulating surfaces 730a, 730b of both implant parts 705a, 705b in the proximal interphalangeal joint prosthesis 700 have to be carefully aligned in relation to each other during the implantation procedure. To facilitate the alignment of the articulation members 720a, 720b in their respective bone fixation members 710a, 710b, the first bore sections 717a, 717b in the respective bone fixation members 710a, 710b are provided with inner cross-sections having a first polygonal outline 719a, 719b. Preferably the first polygonal outlines 719a, 719b of the inner bore first bore section 717a, 717b in the proximal phalanx bone fixation member 710a as well as the intermediate phalanx bone fixation member 710b have a hexagonal shape. However, it may, as described above, also have an octagonal, dodecagonal or other type of polygonal outline. Insertion and orientation of the proximal bone fixation member 710a and the intermediate phalanx bone fixation member 710b into the distal end of the proximal phalanx 56-II, -III, -IV, or -V, and the proximal end of the intermediate phalanx 57-II, -III, -IV, or -V, respectively, is achieved by means of a screw tool 50 as described above for e.g., the radius hemi prosthesis 100.

[0164] The orientation pins 723a, 723b provided on the proximal phalanx articulation member 720a and distal phalanx articulation member 720b, respectively, each have an outer cross-section with a second polygonal shape 719a, 719b. Preferably the second polygonal shapes 719a, 719b of both orientation pins 723a, 723b are hexagonal. However, the orientation pins 732a, 723b may, as described above also have an octagonal, dodecagonal, or other type of polygonal outline (see Figs. 9d-1 and 9d-2).

[0165] Alignment of the two opposing replacement articulation surfaces 730a, 730b is advantageously performed in two stages. In the first stage, trial articulation members 720a, 720b are inserted into their respective bone fixation members 710a, 710b aiming for a general alignment of their replacement articulation surfaces 730a, 730b such that it reasonably can be expected to articulate with each other in the final implant 700.

[0166] In the second stage, the final orientation of each articulation member 720a, 720b inside its bone fixation member 710a, 710b may be aligned using the actual articulation members 720a, 720b, as already described in detail above. Alignment can be achieved by lifting the articulation member 720a, 720b such that its orientation pin 723a, 723b disengages the first bore section 717a, 717b of the inner bore 716a, 716b, rotating the articulation member 720a, 720b 30° in either a clockwise or counterclockwise direction, and reinserting the articulation member 720a, 720b with its orientation pin 723a, 723b into the first bore section 717a, 717b of the inner bore 716a, 716b. If further fine tuning of the alignment is required, the bone fixation member 710a, 710b may also be slightly rotated using the screw tool 50 to improve the fit. The second stage is repeated for both articulation members 720a, 720b until the optimal alignment of the two-sided flange-shaped replacement articular surface 730a with the partially divided cup-shaped replacement articular surface 730b has been achieved in a manner such that unhindered articulation between the two opposing replacement articular surfaces 730a, 730b is attained.

[0167] Once the optimal alignment has been reached and the hexagonal-shaped orientation pins 723a, 723b of each articulation member 720a, 720b have been secured inside the hexagonal-shaped first bore sections 717a, 717b of the inner bores 716a, 716b in the bone fixation members 710a, 710b, rotation between the articulation members 720a, 720b and their respective bone fixation members 710a, 710b is permanently prevented in the proximal interphalangeal joint prosthesis 700 when finally implanted.

[0168] Under certain circumstances wrist arthrodesis, also known as wrist fusion i.e. , a surgical procedure that aims to permanently fuse the wrist joint is the last option for some patients. It is typically performed to alleviate pain, improve stability, and restore function in individuals with severe wrist arthritis, significant joint damage, or instability. Wrist arthrodesis may also be considered in situations when conservative treatments have failed to provide adequate pain relief and functional improvement in individuals with advanced wrist arthritis. Other situations may be when previous wrist joint replacement surgeries have been unsuccessful or have resulted in complications.

[0169] Figs. 10a-c and 11a-c are views of two different alternative wrist arthrodesis implants 800, 900 that may provide relief for patients suffering from significant joint damage or failed previous wrist replacement surgeries in the carpometacarpal joint 43-III.

[0170] The wrist arthrodesis implants 800, 900 in Figs.10a-c and 11a-c comprise bone fixation members 810a, 810b, 910a, 910b that are identical to the bone fixation members 10a, 10b, 410a, 410b found in the two-membered wrist joint implants 1, 400 as seen in Figs. 3a and 6a respectively. Both arthrodesis implants 800, 900 comprise a radius implant part 805a, 905a with a first bone fixation member 810a, 910a configured to be implanted into the cortical bone at the distal end of the radius 51 , and a metacarpal implant part 805b, 905b with a second bone fixation member 810b, 910b configured to be inserted through capitate 54c and into the cancellous and cortical bone of the third metacarpus 55-III.

[0171] Both the radius bone fixation member 810a, 910a and the metacarpal bone fixation member 810b, 910b are advantageously provided with inner bore sections 817a, 817b, 917a, 917b having a first polygonal outline 819a, 819b, 919a, 919b identical to the first polygonal outline 119 described in connection with the hemi prosthesis 100 in Fig. 2j. Preferably the first polygonal outlines 819a, 819b, 919a, 919b are hexagonal outlines. However, since arthrodesis wrist implants fuse the wrist the arthrodesis implants 800, 900 of Figs.10a-c and 11a-c do not include articulation members that allow for articulation of the joint. Instead, the arthrodesis wrist implants 800, 900 include a connector 870, 970 that will fuse the joint at a fixed angle between the first and second bone fixation members 810a, 810b, 910a, 910b.

[0172] In the arthrodesis implant 800 as seen in Fig.10a-c, the connector is a double taper connector 870. The double taper connector 870 is a solid rigid one-piece connector between the radius bone fixation member 810a and the metacarpal bone fixation member 810b. It may be available as a straight link between the two bone fixation members 810a, 810b (not shown) or with a 15° angle as seen in Figs. 10b and 10c.The double taper connector 870 comprises a first orientation pin 823a provided at the proximal end of the double taper connector 870 configured to be inserted to the bore 817a of the radius bone fixation member 810a, and a second orientation pin 823b provided at the distal end of the double taper connector 870 configured to be inserted into the bore 817b of the metacarpal bone fixation member 810b. Both orientation pins 823a, 823b of the double taper connector 870 have second polygonal outlines 829a, 829b like the second polygonal outline 129 described e.g. for the hemi prosthesis 100 in Figs. 2j. Preferably the second polygonal outlines 829a, 829b are dodecagonal outlines.

[0173] The arthrodesis wrist joint 900 disclosed in Fig. 11a-c differs from the double taper wrist arthrodesis 800 in that the connection between the radius bone fixation member 910a and the metacarpal bone fixation member 910b is adjustable. The adjustable radius metacarpal connector 970 comprises two parts: a metacarpal taper part 980 configured to be connected to the metacarpal bone fixation member 910b, and a radius connector part 990 configured to be connected to the radius bone fixation member 910a (see Fig. 1c).

[0174] The metacarpal taper part 980 has a distal end 981 provided with an orientation pin 923b having a second polygonal outline 929b like the second polygonal outline 129 described e.g. for the hemi prosthesis 100 in Figs. 2j. The metacarpal taper part 980 further comprises proximal end 982 with a distal hole 986 forming the center of rotation for the adjustable connector 970 and three proximal holes that may, as seen in Fig. 11c, form one elongated hole 987 that is used to set the angle of the wrist function to one of 0°, 15° or 30°.

[0175] The radius connector part 990 has a proximal member 991 and a distal member. The proximal member 991 is provided with an orientation pin 923a having a second polygonal outline like the second polygonal outline 129 described e.g. for the hemi prosthesis 100 in Figs. 2j. The distal end of the proximal member 992 is provided with a U-shaped cleft 993 with a first leg 994a, and a second leg 994b wherein each leg 994a, 994b is provided with a distal hole 996a, 996b and a proximal hole 997a, 997b.

[0176] The proximal end 982 of the metacarpal taper part 980 is configured to be inserted between the two walls 994a, 994b at the distal end 992 of the radius connector part 990 and fixed thereto with a distal lock screw 998 and a proximal lock screw 999. The distal lock screw 998 is inserted into the distal hole 996a provided on the first leg 994a of the U- shaped cleft 993, through the distal hole 986 provided on the proximal 982 end of the metacarpal taper part 980 and thereafter into the distal hole 996b provided on the second leg 994b of the U-shaped cleft 993. The distal lock screw 998 forms the rotation axis when the angle of the wrist shall be set.

[0177] After the angle for the optimal wrist function has been determined, the proximal lock screw 999 is inserted into the proximal hole 997a provided on the first leg 994a of the U-shaped cleft 993, through one of the three hoes forming the proximal hole 987 provided on the proximal 982 end of the metacarpal taper part 980 and thereafter into the proximal hole 997b provided on the second leg 994b of the U-shaped cleft 993. The proximal lock screw 999 locks the angle of the wrist joint in a fixed position.

[0178] Unless they are already osseointeg rated for a previous wrist joint prothesis that has failed, the bone fixation members 810a, 810b, 910a, 910b of the radius and metacarpal implant parts 805a, 805b, 905a, 905b are advantageously first inserted in the radius 51 and metacarpal bones 55-III respectively. Both bone fixation members 810a, 810b, 910a, 910b must be fully integrated before connecting the double taper connector 820 or the adjustable connector 920.

[0179] The radius bone fixation member 810a, 910a is positioned into cancellous and cortical bone of the distal end of the radius 51 and the metacarpal bone fixation member 810b, 910b is inserted into the cancellous and cortical bone at the proximal end of the metacarpus 55-III.

[0180] Although the arthrodesis implants 800, 900 are less prone to dislocation compared to articulating wrist arthroplasty implants such as e.g., the two membered wrist implants in Fig. 3a and 6a, precise alignment of the double taper connection 820 or the adjustable radius metacarpal connector 920 in relation to the first and second bone fixation members 810a, 810b, 910a, 910b is still important. As described above for e.g., the radius bone fixation member 110 in the radius hemi prosthesis 100, the bone fixation members, 810a, 810b, 910a, 910b are inserted and fixed to their respective bones by means of the screw tool 50 as seen in Fig. 13

[0181] When connecting the double taper connector 870 or the adjustable connector 970 to their respective bone fixation members 810a, 810b, 910a, 910b the distal ends are advantageously connected to the metacarpal bone fixation members 810b, 910b before the proximal ends are connected to the radius bone fixation members 810a, 910a. Both connectors 870, 970 may, due to the second polygonal outlines of their orientation pins 823b, 923b, be rotated 30° stepwise either in the clockwise or counterclockwise direction inside the inner bores to orient the fixed angle of the connectors 870, 970 into an optimal alignment with the metacarpus bones 55-III.

[0182] A further objective of the present disclosure is to provide a modular prostheses system that offers salvage options that limit unnecessary implant removal by taking advantage of preexisting stable and osseointegrated implants. The various prostheses 100, 200, 1 , 400, 800, 900 configured to replace the radiocarpal joint 41 or the carpometacarpal joint 43-III as described herein allow for easy conversion between different types of implants while at the same time minimizing bone loss which would otherwise occur during removal of well- fixed implants.

[0183] The implants of the modular protheses system may, e.g., allow conversion from a hemi radius prosthesis 100 or 200 as seen in Figs. 2a and 4a respectively to one of the twomembered radiocarpal wrist implants 1 , 400 with preserved wrist motion as seen in Figs. 3a and 6a respectively. Alternatively, they may be converted to one of the radiocarpal arthrodesis implants 800, 900 wherein the wrist joint is fused as seen in Figs. 10a-c or 11- a-c. In still a further alternative the two-membered wrist joint prostheses 1 , 400 may be converted to one of the radiocarpal arthrodesis implants 800, 900.

[0184] It is thus a further aim of the present disclosure to provide a modular prostheses system for joints in wrist which may provide a bone preserving salvage procedure if a previously implanted wrist prosthesis for some reason starts creating complications or fails to function properly.

[0185] As evident from the disclosure above and regardless of whether the prostheses configured to be implanted in the radiocarpal joint 41-1 or the carpometacarpal joint 43-111 they all comprise at least a first bone fixation member 110, 210, 10a, 410 configured to be implanted in the distal end of a radius bone 51. A first articulation member 120, 220, 20a, 420a is arranged to be inserted in the bore 116, 216, 16a, 416a of the bone fixation member 110, 210, 10a, 410. Depending on the severity of joint failure, the first articulation member 120, 220, 20a, 420a is configured to articulate with an opposing articular surface arranged one or more proximal surfaces of the carpals forming a hemi radius prosthesis 100 or 200 as seen in Fig. 2a or Fig. 4a. Alternatively the first articulation member 20a, 420a is configured to articulate with a second articulation member 20b, 420b connected to a second bone fixation member 10b, 410b of a metacarpal implant part 10b, 400b as seen in Figs. 3b and 6a.

[0186] The arthrodesis wrist implants 800, 900 disclosed herein do not comprise articulation members as the two-membered radiocarpal wrist implants 1, 400. Instead, they comprise connectors 870, 970 that fuse carpometacarpal joint 43-II into a fixed angle that prevents further articulation of the joint. However, since both the double taper arthrodesis 800 and the angle-adjustable arthrodesis 900 comprise radius bone fixation members 810a, 910a and metacarpal bone fixation members 810b, 910b that are identical to the bone fixation members of the failed hemi wrist implants 100, 200 or two-membered radiocarpal wrist implants 1 , 400, any one of the articulation members 120, 220, 20a, b, 420a, b may easily be exchanged for the double taper connector 870 or adjustable connector 970 as required.

[0187] Figs. 12a-g disclose exploded views of the different wrist prostheses of the modular prostheses system described herein. The skilled person can easily see how the bone fixation members implants configured to be inserted into the radius bone 41 have the same configuration and the bone fixation members implants configured to be inserted into the metacarpus bone 55-III have the same configuration. It is the articulation members or alternatively the arthrodesis connectors that differ between the implants. As explained above the first polygonal outline is common to all inner bores of the bone fixation members and the second polygonal outline of the orientation pins is common to all articulation members and arthrodesis connectors. This enables easy conversion between the different types of prostheses without having to remove already well osseointegrated implants.

[0188] The terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms "comprises," "comprising," "includes," and / or "including" when used herein specify the presence of stated features, integers, actions, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, actions, steps, operations, elements, components, and / or groups thereof.

[0189] It will be understood that, although the terms first, second, etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element without departing from the scope of the present disclosure.

[0190] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0191] It is to be understood that the present disclosure is not limited to the aspects described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the present disclosure and appended claims. In the drawings and specification, there have been disclosed aspects for purposes of illustration only and not for purposes of limitation, the scope of the disclosure being set forth in the following claims.

Claims

CLAIMS1 . A wrist joint prosthesis (400) configured for implantation in a carpometacarpal joint in the wrist, said prosthesis (400) comprising a radius implant part (405a) configured to be inserted into a distal end of a radius bone (51) of the radiocarpal joint (41), and a metacarpal implant part (405b configured to be inserted into a proximal end of a metacarpal bone (55-III) in the radiocarpal joint (41),- the radius implant part (405a) comprising a radius bone fixation member (410a) and a radius articulation member (420a) provided with an asymmetrically cupshaped replacement articulation surface 430a, , the radius articulation member (420a) being configured to be received in the radius bone fixation member (410a) in a releasable manner,- the metacarpal implant part (405b) comprising a metacarpal bone fixation member (410b) and a metacarpal articulation member (420b) provided with a ballshaped replacement articulation surface (430b), the metacarpal articulation member (420b) being configured to be received in the metacarpal bone fixation member (410b) in a releasable manner, wherein- the radius bone fixation member (410a) comprising a central axis (A) extending from a first end (411a) to a second end (412a) of the radius bone fixation member (410), the bone fixation member (410a) further comprising an inner bore (416a) extending from a surface (415a) on the second end (412a) towards the first end (411a) of the first bone fixation member (410a), the inner bore (416a) comprising two or more bore sections (417a, 418a) being centered, or substantially centered along the central axis (AAa) extending through the radius bone fixation member (410a), wherein a first bore section (417a) is configured for receiving an orientation pin (423a) arranged on the radius articulation member (420a); and wherein- the radius articulation member (420a) has a first portion (421a) and a second portion (422a), the first portion (421a) comprising the orientation pin (423a) configured to be inserted into the first bore section (417a) of the inner bore (416a) and, when seated inside the first bore section (417a), the first portion (421a) with the orientation pin (423a) is centered or substantially centered along the central axis (AAa) of the radius bone fixation member (410a) and thereby forming a common central axis (AAa) extending through the radius bone fixation member (410a) and the radius articulation member (420a); and the second portion (422a) of the radius articulation member (420a) comprising aradius replacement articular surface (430a) configured for articulation with an opposing articular surface provided by the ball-shaped replacement articulation surface (430b) arranged on the metacarpal articulation member (420b), characterized in that when the radius articulation member (420a) with the orientation pin (423a) is seated inside the inner bore (416a), the radius replacement articular surface (430a) has a configuration that extends in three directions x, y and z; wherein the first direction (x) extends along the common central axis (AAa) formed between the radius bone fixation member (410a) and the radius articulation member (420a); and the second direction (y) extends perpendicular to the first direction (x); and the third direction (z) extends perpendicular both to the first direction (x) and second direction (y), such that the radius replacement articular surface (430a) has an extension in the yz-plane that is asymmetric about the common central axis (AAa) of the radius bone fixation member (410a) and the radius articulation member (420a); and wherein- the first bore section (417a) of the inner bore (416a) has an cross-section extending perpendicularly to the central axis (A) of the bone fixation member (410a), the cross-section of the first bore section defining a first polygonal outline (419a); and- the orientation pin (423a) has a cross-section defining a second polygonal outline (429a), such that when the radius articulation member (420a) with the orientation pin (423a) is seated in the inner bore (416a) of the radius bone fixation member (410a), rotation of the radius articulation member (420a) in relation to the radius bone fixation member (410a) is prevented.

2. The prosthesis (400) according to claim 1, wherein the radius bone fixation member (410a) has an exterior conical shape provided with outer threads (414a).

3. The prosthesis (400) according to claim 2, wherein the outer threads (414a) are self-tapping.

4. The prosthesis (400) according to any one of the preceding claims, wherein the orientation pin (423a) is provided at a first end of a shaft (424a), said shaft (424a) having an outer configuration adapted to be inserted into a second bore section (418a) of the inner bore (416a) of the bone fixation member (410a).

5. The prosthesis (400) according to claim 4, wherein the first and second bore sections (417a, 418a) of the inner bore (416a) are centered or substantially centered along the central axis (A) of the radius bone fixation member (410a).

6. The prosthesis (400) according to any one of the preceding claims, wherein the first polygonal outline (419a) is hexagonal.

7. The prosthesis (400) according to any one of the preceding claims, wherein the second polygonal outline (429a) is dodecagonal.

8. The prosthesis (400) according to any one of claims 1 to 5, wherein both first and second polygonal outlines (419a, 429a) are similar.

9. The prosthesis (400) according to claim 8, wherein both first and second polygonal out lines (419a, 429a) are hexagonal.

10. The prosthesis (400) according to claim 8, wherein both first and second polygonal outlines (419a, 429a) are dodecagonal.

11. The prosthesis (400) according to any one of the preceding claims 1-5, wherein the first polygonal outline (419a) is hexagonal, and the second polygonal outline (429a) is dodecagonal.

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