Radial capitellum prosthesis

Abstract

A radial capitellum prosthesis (1), comprising: - a radial head (2) shaped and designed to engage the humeral capitellum (3) of a patient; - a bipolar collar (4) rotatably associated with the radial head (2) by means of a ball joint (5) defined, with respect to the radial head (2), at the opposite end with respect to the end designed to engage the radial head; - a radial stem (6) associated with the bipolar collar (4) at the opposite end with respect to the ball joint (5) and designed to be fitted onto the distal end of the previously-prepared radius (7) of a patient.

Description

[0001] RADIAL CAPITELLUM PROSTHESIS

[0002] The present invention relates to a radial capitellum prosthesis, as well as to the prosthetic set comprising the components of such prostheses.

[0003] The radial capitellum or radial head is contained in the elbow: it is a particularly complex joint, in terms both of the various skeletal structures that make it up and of the ligamentous and capsular structures.

[0004] Involvement of the radial capitellum in an injury can result in an instability of the elbow that often conditions the recovery and possible outcomes of joint function.

[0005] Radial capitellum prostheses have been developed to reduce the potential complications resulting from resection (removal) surgery on the radial head, which at one time was the only surgical solution, when fragmentation of the radial capitellum made osteosynthesis impossible.

[0006] The contacts between the anteromedial facet of the coronoid process and the medial lip of the trochlea of the ulna and of the radial capitellum with the humeral capitellum represent the most important stabilizing columns of the elbow.

[0007] This intrinsic stability of the bone is reinforced by capsuloligamentous structures represented by the medial collateral ligament (MCL) and by the lateral collateral ligament (LCL).

[0008] So to sum up, the stability of the elbow is ensured by static and dynamic joints.

[0009] The static joints, in turn, are divided into primary joints: the ulnar- humeral joint (olecranon and coronoid), MCL and LCL; and secondary joints: radial capitellum and articular capsule.

[0010] The dynamic joints are represented by the muscles that pass through the elbow: flexo-pronator muscles and extensor-supinator muscles.

[0011] The specific role performed by the radial capitellum in the stability of the elbow has been well described by Hammacher with his “Greek temple” model: according to this model, in the event of isolated fractures of the radial capitellum, resection of the head alone does not cause joint instability; but if the fracture of the head is associated with damage to the MCL or to the interosseous membrane, the entire structure will become unstable.

[0012] For this reason, the synthesis or the positioning of prostheses of the radial capitellum in its anatomical seat, together with repair of the interosseous membrane, fully restores joint stability.

[0013] The radial capitellum represents a secondary stabilizer of the elbow for varus / valgus and posterolateral stresses, and the primary opponent of proximal migration of the radius. Its importance becomes crucial in the event of injury to the lateral (LCL) or medial (MCL) collateral ligament or to the interosseous membrane. Faced with a fracture of the radial capitellum that cannot be synthesized with a sufficient stability of the elbow to permit an early mobilization, it is necessary to decide whether to proceed with a straightforward resection or whether a prosthetic substitution is beneficial.

[0014] On the other hand, contraindications are raised by the possibility of synthesizing the capitellum, and the presence of infective processes.

[0015] Current implants are modular, making it possible to pair different dimensions of heads and stems in order to arrive at the best match between patient anatomy and prostheses.

[0016] The many combinations possible make it possible to reproduce the size and shape of the original radial head as faithfully as possible.

[0017] It should be emphasized that the correct dimensioning of the radial stem, of the head of the capitellum and the offset (length) of the radial capitellum prosthesis are technical objectives.

[0018] Over-dimensioning and lengthening are well-identified complications that determine significant alterations of elbow biomechanics. An excessive lengthening of over 2.5 mm of the radius with prostheses causes a varus deformity of the ulna and its external rotation.

[0019] For the radial capitellum prosthesis, revision of painful lengthening to a total elbow prostheses is not a favorable option, since the total elbow arthroplasty displays high rates of complications and a limited survival time in younger injury patients, who are typically affected by lengthening.

[0020] Cases with signs of excessive lengthening can reach 13-23% of implanted prostheses.

[0021] Excessive shortening is also a cause of an unfavorable outcome, as this condition causes an instability of the elbow, owing to a lack of the stabilizing function already described in the introduction.

[0022] It is therefore necessary for it to be possible to adapt the radial capitellum prosthesis to the correct length during the operation, after the stem has been implanted in the radius.

[0023] The aim of the present invention consists in providing a radial capitellum prosthesis of the modular type that makes it possible to provide a prosthetic implant that offers the broadest guarantees of anatomical compatibility with the elbow joint of the patient, in so doing overcoming the limitations of the prior art described above.

[0024] Within this aim, an object of the present invention consists in providing a radial capitellum prosthesis that is capable of offering the broadest guarantees of reliability, efficiency and operation.

[0025] This aim and this and other objects which will become better evident hereinafter are achieved by a radial capitellum prosthesis, characterized in that it comprises:

[0026] - a radial head shaped and designed to engage the humeral capitellum of a patient;

[0027] - a bipolar collar rotatably associated with said radial head by means of a ball joint defined, with respect to said radial head, at the opposite end with respect to the end designed to engage said radial head;

[0028] - a radial stem associated with said bipolar collar at the opposite end with respect to said ball joint and designed to be fitted onto the distal end of the previously -prepared radius of a patient. Moreover, this aim and this and other objects which will become better evident hereinafter are also achieved by a prosthetic set, particularly for implanting a prostheses as above, characterized in that it comprises:

[0029] - a plurality of sizes of said radial head, to be chosen according to the size of the humeral capitellum it has to engage;

[0030] - a plurality of sizes of said bipolar collar, to be chosen according to the height of the radial capitellum prosthesis after inserting said radial stem into said distal end of the previously-prepared radius of a patient;

[0031] - a plurality of sizes of said radial stem.

[0032] Further characteristics and advantages of the invention will become more apparent from the detailed description of a preferred, but not exclusive, embodiment of a radial capitellum prosthesis, illustrated by way of non-limiting example with the aid of the accompanying drawings wherein:

[0033] - Figure 1 is a perspective view of the prosthesis according to the invention;

[0034] - Figure 2 is a perspective view of the radial head of the prosthesis shown in Figure 1;

[0035] - Figure 3 is a perspective view of the bipolar collar of the prosthesis shown in Figure 1;

[0036] - Figure 4 is a perspective view of the radial stem of the prosthesis shown in Figure 1;

[0037] - Figure 5 is an axial cross-sectional view of the radial head shown in Figure 1;

[0038] - Figure 6 is an axial cross-sectional view of the prosthesis shown in Figure 1;

[0039] - Figure 7 is a side view of a prosthetic set according to the invention;

[0040] - Figure 8 is a schematic view of a prosthetic implant executed by means of the prosthesis shown in Figure 1.

[0041] With reference to the figures, according to the invention, the radial capitellum prosthesis, generally designated by the reference numeral 1, comprises:

[0042] - a radial head 2 shaped and designed to engage the humeral capitellum 3 of a patient;

[0043] - a bipolar collar 4 rotatably associated with the radial head 2 by means of a ball joint 5 defined, with respect to the radial head 2, at the opposite end with respect to the end designed to engage the radial head 2;

[0044] - a radial stem 6 associated with the bipolar collar 4 at the opposite end with respect to the ball joint 5 and designed to be fitted onto the distal end of the previously-prepared radius 7 of a patient.

[0045] In more detail, the radial head 2 has a geometry that is substantially axially symmetric with respect to an axis of revolution 8, with a first portion

[0046] 9 having a substantially disk-like geometric shape and with a second portion

[0047] 10 having a substantially frustoconical radiused geometric shape which extends, at its radially wider part, from the first portion 9 along the axis of revolution 8.

[0048] Advantageously, the first portion 9 has a concave base 11 so as to define an anatomical surface for engagement with the humeral capitellum 3 with a degree of freedom of self-alignment substantially equal to 10°.

[0049] Equally advantageously, the second portion 10 has, at its radially narrower part, a substantially spherical open cavity 12 which partially defines the ball joint 5.

[0050] In the embodiment proposed, the radial head 2 is made of polyethylene (“PE”) in order to reduce its rigidity in contact with the humeral capitellum and the first portion 9 is coated with a biocompatible ceramic coating of titanium niobium nitride (“TiNbN”) so that the anatomical surface defined by this first portion 9 is hypoallergenic and the second portion 10 is radiolucent.

[0051] Considering the bipolar collar 4, this has an axially symmetric geometric shape, with a proximal portion 13 having a substantially spherical geometric shape arranged within the cavity 12 of the radial head 2 in order to define the ball joint 5 and with a distal portion 14 having a substantially frustoconical geometric shape arranged within a respective seat 15 defined in the radial stem 6.

[0052] In more detail, a central portion 16 is comprised between the proximal portion 13 and the distal portion 14 and has a substantially frustoconical geometric shape with the radially wider base directed toward the proximal portion 14.

[0053] In the embodiment proposed, the bipolar collar 4 is made of an alloy of titanium, aluminum and vanadium and the proximal portion 13 is coated with a biocompatible ceramic coating of titanium niobium nitride (“TiNbN”) so as to give greater hardness to the joint surface and ensure greater resistance to wear of the radial head 2.

[0054] Differently, the radial stem 16 has a geometric shape that is elongated along a preferred direction with a surface porosity of a three-dimensional type for cementless fixing to the radius.

[0055] Conveniently, such radial stem 16 defines the seat 15 mentioned above for its connection with the distal portion 14 of the bipolar collar 5.

[0056] Advantageously, the radial stem 16 is provided by three-dimensional printing of powder of the titanium, aluminum and vanadium alloy which, preferably, is the Ti6A14V alloy.

[0057] According to the invention, for the implantation of the prosthesis 1, a prosthetic set 100 is supplied which comprises:

[0058] - a plurality of sizes of the radial head 2, to be chosen according to the size of the humeral capitellum 3 it has to engage;

[0059] - a plurality of sizes of the bipolar collar 4, to be chosen according to the height of the radial capitellum prosthesis after inserting the radial stem 6 into the distal end of the previously -prepared radius 7 of a patient;

[0060] - a plurality of sizes of the radial stem 7;

[0061] - a plurality of trial spacers 17 for identifying the optimal prosthetic height out of the bone;

[0062] - a plurality of trial heads 18 for verifying the optimal prosthetic height out of the bone prior to implantation.

[0063] Conveniently, as will be better described later, the trial spacers 17 and the trial heads 18 are made of a radiolucent material with a radiopaque ring 19 for verifying their correct position relative to the ulnar coronoid process in the trial reduction of the prosthesis 1.

[0064] In the embodiment proposed, the radial heads 2 are differentiated from each other in the diameter of the first portion 9, and the radial head 2 is chosen from the set of radial heads with a diameter of: 17.5mm; 19mm; 20.5mm; 22mm and 23.5mm.

[0065] Differently, the bipolar collars 4 are differentiated from each other in the height of the central portion 16 and the bipolar collar 4 is chosen from the set of bipolar collars with the height of the central portion 16 equal to: 1mm; 2.5mm and 5mm.

[0066] Finally, the radial stems 6 are differentiated from each other in their diameter and the radial stem 6 is chosen from the set of radial stems with diameter equal to: 1mm; 1.5mm; 2mm; 2.5mm; 3mm; 4mm; 5mm; 6mm and 7mm.

[0067] In this manner, the set of instruments of the prosthesis 1 comprises fifteen “trial implants” for assessing the stability of the prosthesis 1, which is defined on the basis of measuring the diameter of the head of the removed radius. Such “trial implants” are radio-transparent and have a radiopaque ring 19 for assessing their correct position with respect to the coronoid process of the ulna.

[0068] The chosen ’’trial implant” is then provisionally implanted in the radial stem 6 (which was previously fixed to the bone using the press-fit technique) for the assessment of elbow stability in flexion / extension.

[0069] The implantation of the prosthesis 1 is then concluded by connecting the radial head 2 to the bipolar collar 5 with the adapted accessory set of instruments and checking the operation in rotation through 10° of the radial head 2 on the bipolar collar 5, prior to fixing the bipolar collar 5 to the radial stem 6, via frustum interlocking and reducing the dislocation of the prosthesis 1, so reconstructing elbow functionality.

[0070] In practice it has been found that the radial capitellum prosthesis and the prosthetic set, according to the present invention, achieve the set aim and objects.

[0071] The radial capitellum prosthesis and the prosthetic set, thus conceived, are susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

[0072] Moreover, all the details may be substituted by other, technically equivalent elements.

[0073] In practice the materials employed, provided they are compatible with the specific use, and the contingent dimensions and shapes, may be any according to requirements and to the state of the art.

[0074] The disclosures in Italian Patent Application No. 102024000009514 from which this application claims priority are incorporated herein by reference.

[0075] Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

CLAIMS1. A radial capitellum prosthesis (1), characterized in that it comprises:- a radial head (2) shaped and designed to engage the humeral capitellum (3) of a patient;- a bipolar collar (4) rotatably associated with said radial head (2) by means of a ball joint (5) defined, with respect to said radial head (2), at the opposite end with respect to the end designed to engage said radial head (2);- a radial stem (6) associated with said bipolar collar (4) at the opposite end with respect to said ball joint (5) and designed to be fitted onto the distal end of the previously-prepared radius (7) of a patient.

2. The prosthesis (1) according to claim 1, characterized in that said radial head (2) has a geometry that is substantially axially symmetrical with respect to an axis of revolution (8), with a first portion (9) having a substantially disk-like geometric shape and with a second portion (10) having a substantially frustoconical radiused geometric shape which extends, at its radially wider part, from said first portion (9) along said axis of revolution (8); said first portion (9) having a concave base (11) so as to define an anatomical surface for engagement with said humeral capitellum (3) with a degree of freedom of self-alignment substantially equal to 10°, and said second portion (10) having, at its radially narrower part, a substantially spherical open cavity (12) which partly defines said ball joint (5).

3. The prosthesis (1) according to claim 2, characterized in that said radial head (2) is made of polyethylene and said first portion (9) is coated with a biocompatible ceramic coating of titanium niobium nitride so that the anatomical surface defined by said first portion (9) is hypoallergenic and said second portion (10) is radiolucent.

4. The prosthesis (1) according to one or more of the preceding claims, characterized in that said bipolar collar (4) has a substantially axiallysymmetric geometric shape, with a proximal portion (13) having a substantially spherical geometric shape arranged within said cavity (12) of said radial head (2) so as to define said ball joint (5) and with a distal portion (14) having a substantially frustoconical geometric shape arranged within a respective seat (15) defined in said radial stem (6); a central portion (16) being comprised between said proximal portion (13) and said distal portion (14) and having a substantially frustoconical geometric shape with the radially wider base directed toward said proximal portion (13).

5. The prosthesis (1) according to claim 4, characterized in that said bipolar collar (4) is made of an alloy of titanium, aluminum and vanadium and in that said proximal portion (13) is coated with a biocompatible ceramic coating of titanium niobium nitride so as to give greater hardness to the joint surface and ensure greater resistance to wear of said radial head (2).

6. The prosthesis (1) according to one or more of the preceding claims, characterized in that said radial stem (6) has a geometric shape that is elongated along a preferred direction with a surface porosity of a three- dimensional type for cementless fixing to the radius, said radial stem (6) defining said seat (15) for its connection with the distal portion (14) of said bipolar collar (4).

7. The prosthesis (1) according to claim 6, characterized in that said radial stem (6) is provided by means of three-dimensional printing from powder of said titanium, aluminum and vanadium alloy.

8. The prosthesis (1) according to claim 6 or 7, characterized in that said titanium, aluminum and vanadium alloy is the Ti6A14V alloy.

9. A prosthetic set (100), particularly for implanting a prosthesis (1) according to one or more of the preceding claims, characterized in that it comprises:- a plurality of sizes of said radial head (2), to be chosen according to the size of the humeral capitellum (3) it has to engage, said radial heads (2)differing from each other in the diameter of said first portion (9);- a plurality of sizes of said bipolar collar (4), to be chosen according to the height of the radial capitellum prosthesis after inserting said radial stem (6) into said distal end of the previously-prepared radius (7) of a patient, said bipolar collars (4) differing from each other in the height of said central portion (16);- a plurality of sizes of said radial stem (6), said radial stems (6) differing from each other in their diameter.

10. The prosthetic set (100) according to claim 9, characterized in that said radial head (2) is chosen from the set of radial heads (2) with a diameter of: 17.5 mm; 19 mm; 20.5 mm; 22 mm and 23.5 mm.

11. The prosthetic set (100) according to claim 9 or 10, characterized in that said bipolar collar (4) is chosen from the set of bipolar collars (4) with the height of said central portion (16) equal to: 1 mm; 2.5 mm and 5 mm.

12. The prosthetic set (100) according to one or more of claims 9 to11, characterized in that said radial stem (6) is chosen from the set of radial stems (6) with a diameter equal to: 1 mm; 1.5 mm; 2 mm; 2.5 mm; 3 mm; 4 mm; 5 mm; 6 mm and 7 mm.

13. The prosthetic set (100) according to one or more of claims 9 to12, characterized in that it comprises a plurality of trial spacers (17) for identifying the optimal prosthetic height out of the bone.

14. The prosthetic set (100) according to one or more of claims 9 to13, characterized in that it comprises a plurality of trial heads (18) for verifying the optimal prosthetic height out of the bone prior to implantation.

15. The prosthetic set (100) according to claims 13 and 14, characterized in that said trial spacers (17) and said trial heads (18) are made of a radiolucent material with a radiopaque ring (19) for verifying their correct position relative to the ulnar coronoid process in the trial reduction of the prosthesis (1).

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