Compliant wrist implant

Abstract

An orthopedic device is disclosed. The device includes a first joint member having a hollow body sized to receive a portion of a second joint member therein. The second joint member is positioned in between and arranged in series with a third joint member and a fourth joint member. The third joint member and fourth joint member are positioned on opposite ends of a crossmember. A first flexure structure flexibly couples together the first joint member and the second joint member. A second flexure structure flexibly couples together the second joint member and the third joint member. A third flexure structure flexibly couples together the second joint member and the fourth joint member. The first joint member, third joint member, and fourth joint member are configured to rotate about the second joint member within two degrees of freedom.

Description

COMPLIANT WRIST IMPLANT CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to US Provisional Patent Application No. 63 / 624,852, filed on January 25, 2024, incorporated herein by reference in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

[0002] This invention was made with government support under 1DP2HD111538-01 awarded by the National Institutes of Health. The government has certain rights in the invention.BACKGROUND

[0003] The wrist is a complex structure that supports the functional abilities of the upper limbs. The wrist enables a high degree of flexibility by allowing the hand to manipulate objects and interact with the environment. Unfortunately, advanced pan carpal pathologies (e.g., bone cell tumors) and high-energy fractures may impair the functionality or reconstruction of the structure of the wrist. Although the wrist motion may be simplified into two degrees of freedom (DOF), biologically, this motion is the result of the interaction of eight bones (i.e., the four bones of the proximal carpal row and the four bones of the distal carpal row). Further, these bones are connected and stabilized by flexible ligaments that permit either large or micro displacements. The intricate anatomical structure of the wrist provides an exceptional degree of maneuverability to the hand, allowing humans to grasp and manipulate objects through different orientations without compensation at the shoulder.

[0004] Wrist compliance may be a fundamental joint characteristic that is attributable to the viscoelastic properties of tissues. When performing a task with the wrist, wrist compliance allows the optimal distribution of forces throughout the joint, thereby preventing load concentration in specific areas. Moreover, in the presence of a load peak, wrist compliance imparts shock-absorbent properties, which prevent harm to bones, ligaments, and tendons. Maintaining optimal joint functionality without introducing excessive constraints or rigidity reduces the risk of cartilage degeneration joint overloading, and tendon stiffening. For instance, the triangular fibrocartilage complex (TFCC), located between the ulnar head and the proximal carpal row, on the ulnar side of the wrist, may provide such joint functionality. A. The TFCCfunctions as a cushion for the wrist joint, allowing for the dissipation and distribution of forces transmitted through the wrist joint, particularly during load-bearing activities. However, during a classic wrist arthroplasty that include excising wrist ligaments, the TFCC is separated from the bones that the complex stabilizes and is often completely lost in the Darrach’s procedure with the ulnar head resection.

[0005] Conventional wrist implants employ a condyloid or a ball-and-socket like mechanisms, either with or without constraints. Unfortunately, conventionally employed wrist endoprosthesis do not maintain or reproduce the biological compliance of the wrist. As such, when the implants are used in high requirement young patients, the conventional wrist endoprosthesis underperform during stability and load bearing activities. Moreover, the axial and transversal loads subjected on the wrist during activities of daily living (ADL), involving minimal load bearing, may be extremely high, particularly when such activities include grip motion. However, as conventional implants lack wrist compliance and are rigidly anchored to bone, the axial load is transferred rigidly to the radius. Additionally, in a healthy wrist joint, the conformation of the carpal bones and other soft tissues, such as the TFCC, contribute to distributing off axis loads and preserving stability. However, the absence of stabilizing soft tissue around the implant may result in subluxation based on slippage of an under constrained articulating joint or dislocation of constrained implants under excessive stress.

[0006] As such, conventional wrist replacements lack the longevity and stability necessary to make total wrist arthroplasty the first-line treatment for active patients, with pan carpal and distal radio-ulnar joint pathologies, requiring invasive intervention. Artificial wrist reconstruction, such as current total wrist arthroplasty (TWA) technique, replaces the complex wrist architecture with unconstrained implants that provide large range of motion. Based on the complex structure of the wrist, the joint’s biological ligaments are lost during the TWA procedure, with the excision of the proximal carpal row and part of the distal carpal row. As a result, unrestrained wrist implants are extremely susceptible to subluxation under load-bearing conditions, frequently leading to painful injuries, accelerated implant wear, and a non-biological distribution of the load on the radial and carpal / metacarpal anchoring bones. Conversely, constrained implants cannot precisely replicate the wrist’s complex biomechanics. By being overly constrained, prostheses introduce load-bearing and anchoring disadvantages that frequently lead to loosening, especially at the metacarpal attachment. Moreover, the joint’s endoprosthesis integration requires the presence ofviable bone stock, the absence of which renders wrist fusion the only viable option. The potential risks of an unstable anchoring and subsidence in fact overcome the benefits of the implant. Further, bone resorption and aseptic loosening are additional similar limitations that reduce the life span of such implants. For instance, bone resorption and aseptic loosening are caused by synthetic particulates of the implant, which are released due to prolonged frictional contact between articulating surfaces.

[0007] The resultant instability of these implants leads to painful injuries, accelerated implant wear, and non-biological load distribution on anchoring bones, all of which limit the longevity of these artificial reconstructions in the body. Given these limitations, the preferred treatment for complex pan-carpal pathologies, especially in patients facing extensive bone loss, is total wrist arthrodesis. Arthrodesis is extremely effective in restoring the structure and stability of the wrist but does so by eliminating the wrist joint and all its motion. As such, patients with wrist arthrodesis exhibit decreased functionality and excessive compensatory shoulder motion, which can cause other joint pathologies over time.

[0008] Thus, there is a need in the art for compliant wrist implants that provide long-term and stable reconstruction of the wrist while maintaining optimal joint functionality. The present invention satisfies this need.SUMMARY

[0009] The present disclosure relates generally to implants, and more particularly, to a compliant wrist implant.

[0010] In one or more aspects, the disclosed technology relates to an orthopedic device. In one or more cases, the orthopedic device comprises a first joint member having a hollow body sized to receive a portion of a second joint member therein. In one or more cases, the second joint member is positioned in between and arranged in series with a third joint member and a fourth joint member. In one or more cases, the third joint member and fourth joint member are positioned on opposite ends of a crossmember. In one or more cases, a first flexure structure flexibly couples together the first joint member and the second joint member. In one or more cases, a second flexure structure flexibly couples together the second joint member and the third joint member. In one or more cases, a third flexure structure flexibly couples together the second joint member and the fourth joint member. In one or more cases, the first joint member, thirdjoint member, and fourth joint member are configured to rotate about the second joint member within two degrees of freedom.

[0011] In one or more aspects, the disclosed technology relates to an orthopedic device. In one or more cases, the orthopedic device comprises a housing having a hollow body. In one or more cases, the orthopedic device comprises a compression joint. In one or more cases, a portion of the compression joint is sized and configured to rotate within the housing about an axis along which a force is applied to the orthopedic device. In one or more cases, the joint comprises groupings of positive stiffness flexures and groupings of negative stiffness flexures disposed between a first end portion and a second end portion of the joint. In one or more cases, the groupings of positive stiffness flexures and groupings of negative stiffness flexures are circumferentially and intermittently disposed around the joint. In one or more cases, an arrangement of the groupings of positive stiffness flexures is configured to negate stiffness exhibited by the groupings of negative stiffness flexures in a preloaded state.

[0012] A variety of additional aspects will be set forth in the description that follows. The aspects can relate to individual features and to combination of features. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad inventive concepts upon which the embodiments disclosed herein are based.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The following drawings are illustrative of particular embodiments of the present disclosure and therefore do not limit the scope of the present disclosure. The drawings are not to scale and are intended for use in conjunction with the explanations in the following detailed description.

[0014] FIG. 1 illustrates a perspective view of an example compliant wrist implant.

[0015] FIG. 2A illustrates a perspective view of the example compliant wrist implant of FIG. 1 positioned in a flexion / extension configuration.

[0016] FIG. 2B illustrates a front view of the example compliant wrist implant of FIG. 1 positioned in a radio / ulnar deviation configuration.

[0017] FIG. 2C illustrates another perspective view of the example compliant wrist implant of FIG. 1 positioned in a flexion / extension and radio / ulnar deviation configuration.

[0018] FIG. 3 A illustrates a side view of the example compliant wrist implant of FIG. 1 configured in an example lateral hard-stop engagement position.

[0019] FIG. 3B illustrates a side view of the example compliant wrist implant of FIG. 1 configured in an example vertical hard-stop engagement position.

[0020] FIG. 4 illustrates the example compliant wrist implant having proximal and distal anchors.

[0021] FIG. 5 A illustrates a top-down view of the example compliant wrist implant of FIG. 1 implanted with a radial and carpal fixation to a wrist.

[0022] FIG. 5B illustrates is a perspective view of the example compliant wrist implant of FIG. 1 implanted with a radial and carpal fixation to a wrist.

[0023] FIG. 5C is a top-down view of an example compliant wrist implant implanted into a wrist of a subject, and an example cover enclosing the compliant wrist implant.

[0024] FIG. 5D is another top-down view of the example compliant wrist implant implanted into a wrist of a subject.

[0025] FIG. 6 illustrates example results for Finite Element Analysis (FEA) stress testing of the example compliant wrist implant, illustrated in FIGs. 5C and 5D.

[0026] FIG. 7A illustrates a perspective view of another example implant.

[0027] FIG. 7B illustrates a perspective view of the example implant of FIG. 7A in a disassembled state.

[0028] FIGs. 7C and 7D illustrates a perspective view of an example joint of the example implant of FIG. 7A, in which FIG. 7D is an enlarged view of FIG. 7C.

[0029] FIG. 8A illustrates an isometric view of the example joint of FIG. 7C in which a positive stiffness flexure portion is shown.

[0030] FIG. 8B illustrates a side view of the example joint of FIG. 7C in which a positive stiffness flexure portion is shown.

[0031] FIG. 8C illustrates a top view of the example joint of FIG. 7C in which a positive stiffness flexure portion is shown.

[0032] FIG. 8D illustrates a bottom view of the example joint of FIG. 7C in which a positive stiffness flexure portion is shown.

[0033] FIG. 8E illustrates a cross-sectional view of the example joint of FIG. 7C in which a positive stiffness flexure portion is shown.

[0034] FIG. 8F illustrates a cross-sectional view of the example joint of FIG. 7C in which a positive stiffness flexure portion is shown.

[0035] FIG. 8G illustrates another isometric view of the example joint of FIG. 7C in which a positive stiffness flexure portion is shown.

[0036] FIG. 9A illustrates a side view of the example joint of FIG. 7C in which a positive stiffness flexure portion and a negative stiffness flexure portion are shown.

[0037] FIG. 9B illustrates a top view of the example joint of FIG. 7C in which a positive stiffness flexure portion and a negative stiffness flexure portion are shown.

[0038] FIG. 9C illustrates a bottom view of the example joint of FIG. 7C in which a positive stiffness flexure portion and a negative stiffness flexure portion are shown.

[0039] FIG. 9D illustrates a cross-sectional view of the example joint of FIG. 7C in which a positive stiffness flexure portion and a negative stiffness flexure portion are shown.

[0040] FIG. 9E illustrates a cross-sectional view of the example joint of FIG. 7C in which a positive stiffness flexure portion and a negative stiffness flexure portion are shown.

[0041] FIGs. 10A and 10B illustrates a process to preload the example implant of FIG. 7A.

[0042] FIG. 11 A illustrates the example compliant wrist implant having proximal and distal anchors. FIG. 1 IB illustrates a cross-sectional view of the example compliant wrist implant of FIG. 11 A.

[0043] FIG. 12A illustrates a top-down view of the example compliant wrist implant of FIG.11 A implanted with a radial and carpal fixation to a wrist. FIG. 12B illustrates a side view of the example compliant wrist implant of FIG. 11A implanted with radial and carpal fixation to the wrist.

[0044] FIG. 13 illustrates an example cadaveric dissection to define envelop dimensions of the example compliant wrist implant.

[0045] FIGs. 14A-14C illustrate an example finite element analysis of a mechanical performance of the flexural elements of the example compliant wrist implant flexural elements under different loading conditions.

[0046] FIG. 15 illustrates an unloaded stiffness test showing a torque-angular displacement relationship over a range of motion of the example compliant wrist implant.DETAILED DESCRIPTION

[0047] The following discussion omits or only briefly describes conventional features of implants that are apparent to those skilled in the art. It is noted that various embodiments are described in detail with reference to the drawings, in which like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the claims attached hereto. Additionally, any examples set forth in this specification are intended to be non-limiting and merely set forth some of the many possible embodiments for the appended claims. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations.

[0048] Unless otherwise specifically defined herein, all terms are to be given their broadest reasonable interpretation including meanings implied from the specification as well as meanings understood by those skilled in the art and / or as defined in dictionaries, treatises, etc. It is noted that, as used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless otherwise specified, and that the terms “includes” and / or “including,” when used in this specification, specify the presence of stated features, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0049] Relative terms such as “horizontal,” “vertical,” “up,” “down,” “top,” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing figure under discussion. These relative terms are for convenience of description and normally are not intended to require a particular orientation. Terms including “inwardly” versus “outwardly,” “longitudinal” versus “lateral” and the like are to be interpreted relative to one another or relative to an axis of elongation, or an axis or center of rotation, as appropriate. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. The term “operatively or operably connected” is such an attachment, coupling or connection that allows the pertinent structures to operate as intended by virtue of that relationship.

[0050] Reference throughout the specification to “one embodiment”, “an embodiment” or “some embodiments” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment”, “in an embodiment” or “in some embodiments” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics of “one embodiment”, “an embodiment” or “some embodiments” may be combined in any suitable manner with each other to form additional embodiments of such combinations. It is intended that embodiments of the disclosed subject matter cover modifications and variations thereof. Terms such as “first,” “second,” “third,” etc., merely identify one of a number of portions, components, steps, operations, functions, and / or points of reference as disclosed herein, and likewise do not necessarily limit embodiments of the present disclosure to any particular configuration or orientation.

[0051] Moreover, throughout this disclosure, various aspects of the invention can be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numbers within that range, for example, 1, 2, 2.7, 3, 4, 5, 5.3, 6, and any whole and partial increments there between. This applies regardless of the breadth of the range. As used herein, the term “about” in reference to a measurable value, such as an amount, a temporal duration, and the like, is meant to encompass variations of plus or minus 20%, plus or minus 10%, plus or minus 5%, plus or minus 1%, and plus or minus 0.1% of the specified value, as such variations are appropriate.

[0052] The terms “proximal,” “distal,” “anterior,” “posterior,” “medial,” “lateral,” “superior,” and “inferior” are defined by their standard usage indicating a directional term of reference. For example, “proximal” refers to a position that is situated nearer to the center of a body or point of attachment, while “distal” refers to a position that is situated away from the center of the body or point of attachment. In another example, “anterior” refers to the front of a body or structure,while “posterior” refers to the rear of a body or structure. In another example, “medial” refers to the direction towards the midline of a body or structure, and “lateral” refers to the direction away from the midline of a body or structure. In some examples, “lateral” or “laterally” may refer to any sideways direction. In another example, “superior” refers to the top of a body or structure, while “inferior” refers to the bottom of a body or structure. It should be understood, however, that the directional term of reference may be interpreted within the context of a specific body or structure, such that a directional term referring to a location in the context of the reference body or structure may remain consistent as the orientation of the body or structure changes.

[0053] The terms “patient,” “subject,” “individual,” and the like are used interchangeably herein, and refer to any animal amenable to the systems, devices, and methods described herein. The patient, subject or individual may be a mammal, for example, a human.

[0054] The term “compliant mechanism” refers to a mechanism configured to produce motion and force transmission through the elastic deformation of its flexible components (also known as "flexures"), substitutes of rigid-body linkages or joints. When subjected to an external load, the flexures are capable of bending, twisting, or deforming elastically in precisely tuned ways to produce the desired motion. These slender elements may be designed with specified mechanical properties, such as stiffness and damping, for various degrees of freedom.

[0055] Conventional wrist implants do not maintain or reproduce the biological compliance of a wrist. Embodiments of the present disclosure allow for the reproduction of a biological joint's compliance while introducing inherent stability, thereby providing further advantages of arthroplasty over arthrodesis. Moreover, the disclosed embodiments may recreate the fundamental advantageous characteristics of biological compliance, using cross axis flexural pivots (CAFP). Compliant mechanisms, such as CAFP, may include flexible elements that deform under load to produce desired motion. In contrast to conventional mechanisms, which rely on rigid joints, compliant mechanisms lack rigid connections and traditional hinges. To achieve the desired motion, compliant mechanisms utilize the inherent flexibility (elasticity) and geometry of their structure. The lack of rigid joints allows the complaint mechanism to absorb axial shock and off-axis loads by distributing these loads across the compliant structure (e.g., a flexure). Thus, compliant mechanisms remove the requirement for an articulating surface, allowing the lifespan of the implant to be correlated with the fatigue of the material, as opposed to friction wear.

[0056] Conventional wrist implants employ condyloid or ball-and-socket like mechanisms, either with or without constraints. The embodiments disclosed herein provide an orthopedic wrist implant that includes a plurality of compliant mechanisms arranged in a series configuration to reproduce the wrist joint's biological range of motion, such as the characteristic circumvention motion. The compliant wrist endoprosthesis that preserves wrist motion and guarantees j oint stability. The embodiments disclosed herein provide two main compliant mechanisms (in some examples referred to as flexure structures). One compliant mechanism may replicate the biological flexion / extension motion of the wrist. The other compliant mechanism may be connected in series to the first compliant mechanism and may enable a radio-ulnar deviation motion. Based on the alignment of the rotational axes of the two compliant mechanisms (i.e., two coupled degrees of freedom), the mechanisms may enable a fluid actuation of the circumvention and dart-thrower motion. That is, the mechanisms guide motion of the wrist in two degrees of freedom via elastic deformation, rather than rolling, rubbing, or sliding, as in conventional implants. As such, the embodiments provided herein limit the notorious disadvantages of conventional wrist implants, such as, but not limited to, instability, extremely limited loadbearing capabilities, the need for extensive viable bone stock availability, and the overall longevity of the implant.

[0057] Moreover, the embodiments provide an inherently stable structure, such that the joint has no possibility of subluxation and provides tunable compliance and frictionless constraint that guides motion of the joint without articulation, and therefore with no particulate generation. Additionally, embodiments of the present disclosure may allow high-requirement patients and those affected by extensive bone loss (e.g., those patients having pathologies resulting in the loss or excision of extensive bone in the carpal and distal radio-ulnar region) to utilize the compliant wrist implants described herein. Moreover, embodiments of the present disclosure provide two Degree-of-Freedom natural biomechanics that is load bearing with limited or no rubbing and wear and replicates the natural compliance of wrist soft tissue, accommodating imperfection in the joint and dampening peak loads. Embodiments of the compliant wrist implant are described below with reference to the Figures.

[0058] FIG. 1 illustrates a perspective view of compliant wrist implant 100 (hereinafter “implant 100”). In one or more cases, the implant 100 includes a first anchor 102, a second anchor 104, a first joint member 106, a second joint member 108, a third joint member 110, and a fourth jointmember 1 12 rotatably, hingedly and / or flexibly coupled to one another via a plurality of flexure elements, such as flexure structures 114, 116, and 118. The first joint member 106, second joint member 108, third joint member 110, and fourth joint member 112 may be configured to move relative to each other as described herein.

[0059] In one or more cases, the first joint member 106 may have a rigid body with a hollow center sized to house a portion of the second joint member 108. The rigid body may be sized to allow the portion of the second joint member 108 to rotate therein. The rigid body of the first joint member 106 may include a first curved side 128 and a second curved side 130 disposed between parallel sides 132a and 132b. The first curved side 128 provides a circular or rounded outer geometry to allow the first joint member 106 to rotate in between the third joint member 110 and the fourth joint member 112. The second curved side 130 provides a circular or rounded outer geometry to allow the first joint member 106 to rotate within a portion of the second joint member 108. In one or more cases, an end portion 136 of a flexure 142 of the flexure structure 116 may be coupled to an interior surface 134 of the second curved side 130. In one or more cases, a body of a flexure structure may be coupled to an exterior surface of the first joint member 106. For example, the body 140b of flexure structure 118 may be coupled to an exterior surface of the side 132b of the first joint member 106. In another example, the body 140a of the flexure structure 114 may be coupled to an exterior surface of side 132a of the first joint member 106.

[0060] In one or more cases, the second joint member 108 may have a rigid body with a hollow center sized to house a portion of the first joint member 106. The rigid body may be sized to allow the portion of the first joint member 106 to rotate therein. The rigid body of the joint member 108 may include a flexure side 120 and an anchor side 122 disposed between parallel sides 124a and 124b. The rigid body may be formed in a rectangular-like shape, a cylindrical- like shape, a square-like shape, or the like. In some cases, the outer surface of the rigid body may include a circular or rounded outer geometry to allow the second joint member 108 to rotate within a portion of the first joint member 106. The flexure side 120 of the second joint member 108 may be coupled to an end portion 126 of the flexure structure 116. The anchor side 122 of the second joint member 108 may be coupled with the second anchor 104. The second anchor 104 may be configured to fixedly attach the implant 100 to a body of a subject (e.g., a bone within a wrist of a human). In some cases, the second anchor 104 may include a rod or otherfastener integrated into the second anchor 104 of the implant 100, such that the rod or other fastener may be attached to the body of the subject. In other cases, a rod or other fastener may be removably coupled to the second anchor 104.

[0061] In one or more cases, the third joint member 110 and the fourth joint member 112 may be coupled to one another via a crossmember 138. The crossmember 138 may be a rigid body positioned between the anchor 102 positioned on one side 158 of the crossmember 138 and the third joint member 110 and the fourth joint member 112 positioned on an opposite side 160 of the crossmember 138. The third joint member 110 and the fourth joint member 112 may be positioned on opposite horizontal ends 144a and 144b of the crossmember 138. The distance between the third joint member 110 and the fourth joint member 112 may be large enough to accommodate the first joint member 106 and the second joint member 108 therein. For example, the crossmember 138 may be sized such that the space between the third joint member 110 and the fourth joint member 112 allows for portions of the first joint member 106 and the second joint member 108 to rotate therebetween. For instance, the distance between the third joint member 110 and the fourth joint member 112 may range from 5 millimeters (mm) to 100 mm, or about 5 mm to about 100 mm. The first anchor 102 may be configured to fixedly attach the implant 100 to a body of a subject (e.g., a bone within a wrist of a human). In some cases, the first anchor 102 may include a rod or other fastener integrated into the first anchor 102 of the implant 100, such that the rod or other fastener may be attached to the body of the subject. In other cases, a rod or other fastener may be removably coupled to the first anchor 102. In some cases, the side 158 of the crossmember 138 may include more than one anchor to provide additional fastening points to the body of the subject (e.g., anchors 402a and 402b illustrated in FIG. 4).

[0062] The third joint member 110 may have a rigid body having an interior surface 146 the defines a hollow area of the third joint member 110. The hollow area may be sized to house a portion of the flexure structure 118 and allow the flexure structure 118 to flex and / or rotate therein. The interior surface 146 may be shaped to define a range-limiting element 148 configured to restrict motion, such that the implant 100 is not over-stressed or over-extended. For example, the range-limiting element 148 may be configured to prevent a portion of the flexure structure 118 from articulating beyond a certain range of motion. The range-limiting element 148 may include a curved surface 150 disposed between two surfaces 152a and 152b configured tocontact respective opposing surfaces 154a and 154b of the body 140b of the flexure structure 118. The space between the two surfaces 152a and 152b of the range-limiting element 148 may be increased or decreased to change an overall behavior of the implant 100. For example, by increasing or decreasing the space between the two surfaces 152a and 152b the range of motion, load bearing capacity, stiffness, and the like may also change. The curved surface 150 may be shaped to allow the body 140b of the flexure structure 118 to rotate therein. In one or more cases, the surface 152a of the range-limiting element 148 and the surface 154b of the body 140b may be shaped to interface with one another, and the surface 152b of the range-limiting element 148 and the surface 154a of the body 140b may be shaped to interface with one another. For instance, the surface 152a may include one or more flat surfaces or faces against which respective flat surfaces or faces of the surfaces 154b of the body 140b of the flexure structure 118 press against at the end of a range of motion. In another instance, the surface 152b may include one or more flat surfaces or faces against which respective flat surfaces or faces of the surfaces 154a of the body 140b of the flexure structure 118 press against at the end of a range of motion. In one or more cases, the interior surface 146 of the third joint member 110 may define a flex area 162 sized to allow one or more flexures, such as flexures 164a and 164b to rotate and / or flex therein. End portions 166a and 166b of flexures 164a and 164b may be coupled to the interior surface 146 of the third joint member 110.

[0063] It is noted that the fourth joint member 112 includes one or more of the same or similar features (e.g., but not limited to, the fourth joint member 112 including a range-limiting element 156 therein) as the third joint member 110. As such, a description of such features is not repeated. Further, it is noted that the first joint member 106 includes range limiting element 172 that is configured to contact respective surfaces of the end portion 126 of the flexure structure 116. The range limiting element 172 of the first joint member 106 includes one or more of the same or similar features as the range-limiting element 148 of the third joint member 110. As such, a description of such features is not repeated. Moreover, this disclosure, and features related to implant 100, incorporates the features of international publication number WO2023 / 108094 by reference in its entirety.

[0064] In one or more cases, a flexure structure includes a rigid body and one or more flexures configured to rotatably, hingedly and / or flexibly couple one joint member to another joint member. For example, the first joint member 106 and the third joint member 110 may be coupledto one another via flexure structure 118. That is, the rigid body 140b of the flexure structure 118 may be coupled to an exterior surface of the side 132b of the first joint member 106, and end portions 166a and 166b of flexures 164a and 164b may be coupled to the interior surface 146 of the third joint member 110. Similarly, in another example, the first joint member 106 and the fourth joint member 112 may be coupled to one another via flexure structure 114. That is, the rigid body 140a of the flexure structure 114 may be coupled to an exterior surface of side 132a of the first joint member 106, and end portions of flexures of the flexure structure 114 may be coupled to the interior surface of the fourth joint member 112. In yet another example, the first joint member 106 and the second joint member 108 may be coupled to one another via flexure structure 116. That is, the flexure side 120 of the second joint member 108 may be coupled to an end portion 126 of the flexure structure 116, and the end portion 136 of the flexure 142 of the flexure structure 116 may be coupled to an interior surface 134 of the second curved side 130 of the first joint member 106.

[0065] One or more portions of the flexure structure is configured to deform when one joint member moves relative to a coupled joint member within a degree of freedom. In one or more cases, the degree of freedom is translational. In one or more cases, the degree of freedom is rotational. The flexure structure may include one or more flexures. For example, flexure structure 118 includes flexures 164a and 164b. In another example, flexure structure 116 includes flexure 142. Flexures may be added or removed to the flexure structure to change the overall behavior of the flexure structure. For instance, more or less flexures may change, for example, but not limited to, the range of motion, a load bearing capacity, stiffness, a center of rotation trajectory, and the like. Further, additionally or alternatively to increasing or decreasing a number of flexures, individual characteristics of a flexure may be modified to change the overall behavior of the respective flexure structure. For example, one or more of a length, width, thickness, type of material of the flexure, and the like may be modified to change the range of motion, a load bearing capacity, stiffness, a center of rotation trajectory, and the like.

[0066] In one or more cases, any two flexures, such as flexures 164a and 164b, may have an orientation of any angle 168 relative to each other. For example, angle 168 may be between 0° - 180°, between 0° - 90°, between 0° - 60°, between 0° - 45°, between 0° - 30°, between 0° - 15°, or between 0° - 10°. In another example, angle 168 may be less than or equal to 180°, less than or equal to 170°, less than or equal to 160°, less than or equal to 150°, less than or equal to 140°,less than or equal to 130°, less than or equal to 120°, less than or equal to 1 10°, less than or equal to 100°, less than or equal to 90°, less than or equal to 80°, less than or equal to 70°, less than or equal to 60°, less than or equal to 50°, less than or equal to 40°, less than or equal to 30°, less than or equal to 20°, less than or equal to 10°, less than or equal to 5°, less than or equal to 1°, or about 0°. In one or more cases, the flexures, such as flexures 164a and 164b, may be oriented at the same joint member angle 168 relative to each other between the inner surfaces of flexures 164a and 164b. For example, any two flexures, such as flexures 164a and 164b, may have an orientation of any joint member angle 168 relative to any joint member, such as joint member 110. For instance, angle 168 may be between 0° - 180°, between 0° - 90°, between 0° - 60°, between 0° - 45°, between 0° - 30°, between 0° - 15°, or between 0° - 10°. In other instances, angle 168 may be less than or equal to 180°, less than or equal to 170°, less than or equal to 160°, less than or equal to 150°, less than or equal to 140°, less than or equal to 130°, less than or equal to 120°, less than or equal to 110°, less than or equal to 100°, less than or equal to 90°, less than or equal to 80°, less than or equal to 70°, less than or equal to 60°, less than or equal to 50°, less than or equal to 40°, less than or equal to 30°, less than or equal to 20°, less than or equal to 10°, less than or equal to 5°, less than or equal to 1°, or about 0°.

[0067] In one or more cases, the flexures of a flexure structure may intersect at any point along the length of the flexures. In some cases, a center of rotation of the flexures may be approximated by the intersection point. The center of rotation of the flexures moves as the flexure structure deforms. In one or more cases, flexures of a flexure structure may have different lengths and oriented at any angle, wherein changing any of these properties affects the mechanical behavior of the implant 100. For example, flexures may be oriented such that flexures 164a and 164b form a crossing pattern. In another example, flexures may be oriented such that the flexures of a flexure structure are substantially parallel to one another. In one or more cases, the flexures of the flexure structure 118 and the flexures of the flexure structure 114 may be positioned in parallel with one another. For instance, the flexures of the flexure structure 118 and the flexures of the flexure structure 114 may be formed within the respective joint members such that these flexures are formed as parallel mirror-imaged flexures along their central axis. As such, the parallel configuration may permit precise compliant actuation in one degree of rotational freedom, around the axis that passes through the intersection of both flexures, while exhibiting a high degree of stiffness in the other degrees of motion. Additionally,to further improve load bearing capabilities and reduce parasitic motion, as described herein, one or more additional flexures or an entire CAFP in series in a redundant configuration (a 3 or 4 flexures configuration) may be added.

[0068] In one or more cases, the first joint member 106, second joint member 108, third joint member 110, and fourth joint member 112 may be made from any material known to one skilled in the art, including, but not limited, to metals, metal alloys, polymers, ceramics, metallic glasses, or combinations thereof. In one or more cases, the first joint member 106, second joint member 108, third joint member 110, and fourth joint member 112 may be made from a biocompatible material, such as, but not limited to, Ti-based metallic glass. In one or more cases, the first joint member 106, second joint member 108, third joint member 110, and fourth joint member 112 may be coated in a biocompatible material. In one or more cases, the first joint member 106, second joint member 108, third joint member 110, and fourth joint member 112 may include a titanium alloy, including, but not limited, to Ti6-A14v. In one or more cases, the first joint member 106, second joint member 108, third joint member 110, and fourth joint member 112 may include Cr-Co. In one or more cases, the first joint member 106, second joint member 108, third joint member 110, and fourth joint member 112 may include a stainless steel, including, but not limited, to SS316. In one or more cases, the first joint member 106, second joint member 108, third joint member 110, and fourth joint member 112 may include poly ethene or ultra-high molecular weight polyethylene. In one or more cases, the first joint member 106, second joint member 108, third joint member 110, and fourth joint member 112 may include a composite material, such as, but not limited to, Carbon-PEEK 30. In one or more cases, portions (e.g., portions or all of the range-limiting elements and respective contact surfaces of flexure structures) of the first joint member 106, second joint member 108, third joint member 110, and fourth joint member 112 that are subject to friction and / or wear may be formed from a biocompatible material or coated in a biocompatible material.

[0069] In one or more cases, the implant 100 may be formed by one or more fabrication methods, such as, but not limited to, traditional subtractive manufacturing with no assembly, traditional subtractive manufacturing with assembly, additive manufacturing, and the like. For instance, with respect to traditional subtractive manufacturing with no assembly, the entirety of the implant 100 may be manufactured as a single piece using traditional subtractive methods. In another instance, with respect to traditional subtractive manufacturing with assembly, theimplant 100 may be fabricated via traditional methods as several distinct pieces, which could then be assembled prior to sterilization and implantation. The joints between pieces may be fixed using any number of techniques, including, but not limited to welding, bolting, adhesives, interference fits, or heat-modulated interference fits. In one or more cases, the independent components of implant 100 may be assembled at a low temperature, so that the pieces expand to interference fits when exposed to the body’s heat. In another instance, with respect to additive manufacturing, the implant 100 may be manufactured via 3D printing, either as a single piece or as multiple pieces to be assembled as described above. In one or more cases, the implant 100 may be formed as one component, or many components, and made of one material, or made of multiple materials. The formation of one or more components of the implant 100 may be determined based on one or more of biomechanical, analytical, and finite element modeling, that allows for the optimization of the geometry and arrangement of flexures of the flexure structures based on a predefined biomechanical goal. In one or more cases, the implant 100 is optimized for loading of the implant 100 versus angle profile of the flexures. In one or more cases, the implant 100 is optimized for a predetermined number of loaded cycles per day and / or a maximum resistive load. For example, the number of loaded cycles per day is 1400, and the maximum resistive load is 22 lbs. In one or more cases, the implant 100 is optimized for a pre-determined life span, for example, a life span of 100 years.

[0070] In one or more cases, the implant 100 may reproduce the biomechanical loading behavior of a wrist that allows for the natural dampening of peak loads while maintaining stability and eliminating the risk of subluxations and associated injuries. By adding passive damping capabilities, the implant 100, that replaces the joint with a number of cross-axis flexural pivots, may reduce the peak stresses rigidly transmitted from the metacarpal plate attachment area to the implant 100 and downstream to the radius stem. As such, the implant 100 may prevent loosening at the radial stem and metacarpal region, which is a common occurrence with conventional implants. The implant 100 may, for example, introduce more natural biomechanics that do not place excessive strain on the attachment points, thereby extending the longevity of the attachment area.

[0071] Moreover, given the reduced requirements for available healthy / intact bone stock, the implant 100 may be moved proximally with respect to the radius head while maintaining a stem attachment configuration. This allows qualification of patients with pathologies concurrentlyextending to the radius and ulnar head as well as the proximal carpal row and the proximal end of the distal carpal row. In one or more cases, these bones and the ligaments that connect them can be excided, and their function may be replaced by the compliant wrist implant. Conversely, traditional prostheses require the radius head and the majority of the distal carpal row to be available.

[0072] In addition to addressing issues associated with bone loss, the implant 100 provides stability under loads of up to 10 lbs. This represents an advance over the current standard of care and permits patients to continue engaging in moderate activities. Further, mechanical features, such as hard-stops as described herein, may permit the load capacity to be increased. In one or more cases, the implant 100 may achieve limits close to the lower limit of OSHA's procedures for safe manual weightlifting. Attaining this objective within the first use case permits the expansion of eligibility to high requirement patients. As such, economic issues associated with post-operative lifestyle adjustment that disproportionately affect manual laborers may be resolved or reduced, which. Moreover, the enhancements provided by the implant 100 may reduce restrictions on the post-operative use of the upper limbs during physical activity, creating the potential for an improvement in a patient's overall health.

[0073] Current orthopedic treatments for advanced wrist pathologies are unable to provide patients with long-lasting solutions that can support a lifestyle comparable to that prior to the onset of the pathology. Conventional solutions are either too restrictive, such as arthrodesis, resulting in functional limitations and pathologies related to adaptive compensatory strategies or, for arthroplasty, the conventional solutions are restricted to a low-requirement elderly population that may not face the risk of implant loosening and revision. Based on the entirely unrestrained design of conventional implants, patients are not permitted to lift any weight and are at constant risk of subluxation and injury when engaging in medium to high-demand activities.

[0074] The compliant wrist prosthesis aims to fine-tune an advanced 2 DOF compliant mechanism to overcome the problems associated with the lack of compliance (e.g., arthrodesis) or infinite compliance (e.g., total wrist replacement) that characterize the current standard of care. The approach introduces several advantages related to the implant's more natural biomechanics, such as enhanced load-bearing capacities, inherent stability and durability. Comprised of compliant flexures, the cross-axis pivots are capable of dampening peak loads (i.e., vertical deformation) while also permitting small off-axis load-related deformations (i.e., thedegrees of freedom are not fully constrained). Based on the elastic behavior of flexures, these characteristics are added to the traditional function of the joint as the flexures deform when subjected to a moment about their axis. By utilizing compliance, the implant 100 may not be subject to any form of self-contact during normal, unloaded use, thereby eliminating all friction. This further increases the durability of the implant and eliminates particulate diffusion in the adjacent tissue, which is frequently the cause of osteolysis and subsequent aseptic attachment loosening. Contact may be engaged in the form of a hard-stop when flexures elastically deform to their vertical or lateral design limits and the cross-axis flexural pivot base comes into contact with an articulating surface, allowing motion to continue uninterrupted to the envelope limits, without plastic deformation of the flexures under excessive loads. As such, the hard-stop features may increase previously unattainable loading range limits of the implant 100 without substantially compromising lifespan.

[0075] Moreover, compression or stretching of the radial nerve may occasionally occur during and after TWA surgery, resulting in radial nerve palsy in up to 8% of patients. A medium-term pathology that can affect the activation of extensor muscles, resulting in wrist drop and, in milder cases, implant instability due to laxity of tendons during activity. In the event of development of such a pathology, the elasticity and inherent stability of the implant 100 may provide incredible benefits for an optimal post-operative recovery. Additionally, in order to provide adequate support and drop correction in the rare event that a patient develops a permanent pathology, stiffness of the implant 100 may be adjusted by introducing a spring in parallel with the flexion stage. As such, corrective flexion may be implemented in the implant 100.

[0076] Further, in one or more cases, the joint members of the implant 100 may be assembled in series in a nested configuration to form two flexural joints that allow the respective rotational axes of the flexural joints to be perpendicular to one another while intersecting the same plane. As such, the two flexural joints rotate continuously and without abrupt direction or axis changes. That is, the implant 100 may rotate about two degrees of freedom to approximate and mimic the rotation of a wrist. Moreover, the configuration of the implant 100 may enable a fluid hand circumvention and dart-throwing motion along a 45-degree plane with respect to flexion. For example, as illustrated in FIG. 2A, the first joint member 106, third joint member 110, and fourth joint member 112 may rotate about the second joint member 108 in a direction A to mimic a flexion / extension motion of a wrist. In another example, as illustrated in FIG. 2B, the first jointmember 106, third joint member 110, and fourth joint member 112 may rotate about the second joint member 108 in a direction A to a mimic radio / ulnar deviation motion of a wrist. In another example, as illustrated in FIG. 2C, the first joint member 106, third joint member 110, and fourth joint member 112 may rotate about the second joint member 108 in directions A and B to a flexion / extension motion a mimic radio / ulnar deviation motion of a wrist, thereby allowing for both circumduction and dart thrower motions.

[0077] Dart thrower motion is an essential aspect of wrist ADL performance, which involves a combination of flexion and extension. The mean plane on which such movement occurs is approximately 45 degrees from the deviation plane. In one or more cases, the implant 100, via motion in two degrees of freedom, supports hand circumduction and consequently the dartthrowing motion. Moreover, in applications where the wrist capsule of the patient has considerably small dimensions or where high load bearing requirements are more important than degrees of freedom, the implant 100 may allow a single degree of freedom with an axis rotated by approximately 45 degrees. As such, the implant 100 permits a greater range of motion and load-bearing capacity while still meeting the minimal requirement for enhancing ADL performance with respect to wrist fusion.

[0078] In one or more cases, the flexures and flexure structures described herein can withstand a specified maximum load while in the region of elastic behavior. The implant 100 may utilize hard-stops, such as range-limiting element 148, to increase the load-bearing capacity of the implant 100 and to prevent overextension of the flexures outside their range of motion. For instance, FIG. 3 A illustrates a side view of the implant 100 of FIG. 1 configured in an example lateral hard-stop engagement position 302. As illustrated in FIG. 3A, the range-limiting element 148 may be configured to prevent a portion of the flexure structure 118 from articulating beyond the lateral hard-stop engagement position 302. For instance, in the lateral hard-stop engagement position 302, the surface 152a of the range-limiting element 148 and the surface 154b of the body 140b may interface with one another by pressing against each other at the end of a range of motion, thereby preventing overextension of the flexures outside their range of motion. As illustrated in FIG. 3B, the range-limiting element 148 may be configured to prevent a portion of the flexure structure 118 from articulating beyond the vertical hard-stop engagement position 304. For instance, in the vertical hard-stop engagement position 304, the surface 150 of the range-limiting element 148 may be spaced apart from an articulating surface of the body 140b ofthe flexure structure 1 18, such that the body 140b may rotate within the range-limiting element 148, yet contact each other at the end of a range of motion in the vertical direction, thereby preventing overextension of the flexures outside their range of motion.

[0079] In one or more cases, the hard-stop features may permit the rotating base of the implant 100 to contact another portion of the implant 100 in order to allow direct transmission of vertical stresses, in an articulating surface, or to completely stop motion with a lateral contact of the same base with the end of the range of motion at the stroke-end. That is, as elastic deformation of the flexures is acceptable and functional both vertically and rotationally up to a certain limit, the hard-stops of the implant 100 are configured to prevent plastic deformation of the flexures.

[0080] In one or more other cases, hard-stops may be incorporated into the implant 100 by utilizing one or more ropes and / or cables. Unlike the hard-stops illustrated in FIGs. 3A and 3B, which limit the motion of the flexures via normal contact between implant bodies, the one or more rope and / or cables may limit motion through tensile resistance. This may be advantageous in cases for off-axis loading as the rope and / or cables exist in parallel with the implant 100. As such, the rope and / or cables may not interfere with the intended degrees of freedom. For example, in the implant 100, the rope and / or cables may connect to the center of rotation of the flexure structure and an outer portion of the respective joint member. The one or more ropes may rotate with the joint member, leaving its range of rotation unaffected. However, the one or more ropes may limit the compressive loading experienced by the flexure structure as that loading direction engages the tensile resistance of the rope before compressing the flexures of the flexure structure beyond their elastic region.

[0081] As hard-stops implementation may improve the load-bearing performance of a single degree of freedom, additional benefits may be introduced in a two DOF (and one DOF in certain conditions) compliant implant by limiting the buckling effects caused by off-axis stresses applied to the flexures. These effects may be amplified in the wrist joint, particularly during circumduction motion. In such cases case, a contact feature that engages only under the specific critical loading condition may be added near the connection between one degree of freedom and the other so that no translative load is transmitted as a result of the actuation of the first degree of freedom.

[0082] The embodiments provided herein relate to implanting and / or anchoring implant 100 into one or more bones of a subject. The implant 100 may be divided into two distinct stages. Startingproximally from the radial stem, the first stage enables radio / ulnar deviation actuation. In the second stage, two double-bladed cross axis flexural pivots (CAFP) (e.g., flexure structures 114 and 118) are connected in series, symmetrically, to both lateral extremities of the envelope of the first stage. Based on their symmetrical arrangement, these two CAFPs may be attached in parallel (e.g., act in parallel) to the carpal plate, thereby creating an inherently stable flexion / extension mechanism that encases the preceding one. Based on the compact nature of the implant 100 and the alignment of the axes of rotation of the two stages, which cross in the same transverse plane, the actuation of the two stages enables a fluent actuation of the 2 DOF into a circumduction motion. Although the examples described herein relate to fixing the implant 100 to one or more bones of a wrist of a subject, it should be understood that the implant 100 may be configured such that the implant 100 may be fastened to other joint locations that may utilize two degrees of freedom. For instance, altering the orientation of the second stage of the implant 100 permits the targeting of additional applications that do not necessitate circumvention motion, for example crossing the axis of rotation on the sagittal plane or other configurations.

[0083] The implant 100 may be coupled to one or more bones of a subject using any technique known by one of normal skill in the art. FIG. 4 illustrates the implant 100 having proximal and distal anchors, such as anchors 104, 402a, 402b, and 102. FIGs. 5A and 5B illustrate the implant 100 implanted with a radial and carpal fixation to a wrist 400. In one or more cases, the implant 100 may be anchored, via anchor 104, to bone, such as the radius, using for example, a radius intermedullary fixation with a press-fit, cemented, or compression-style radial stem. In one or more cases, intraosseous rods or pins may also be used to fixate the implant 100 or anchors of the implant 100 to cancellous bone. At the carpal region of the wrist 400, a carpal plate, such as the crossmember 138 of the implant 100 may be attached to the distal carpal row of the wrist 400. The crossmember 138 may be attached to the carpal row via a central stem, such as anchor 102, through the capitate and third metacarpal. Additionally, fasteners 402a and 402b may be attached to the crossmember 138 and carpal row of the wrist 400. For example, fastener 402a may attach the implant 100 to the wrist 400 via the trapezoid and second metacarpal, and fastener 402b may attach the implant 100 to the wrist 400 via the hamate and fourth metacarpal or the hamate alone. In one or more cases, one or more portions of the crossmember 138, anchor 102, and / or fasteners 402a and 402b may be coated with hydroxyapatite or another porous material to promote bone growth and integration in this area, which is prone to loosening.

[0084] In an effort to validate the feasibility and viability of the implant 100 as an alternative implant to total wrist fusion for patients with extensive bone damage and loss, experimental examples were performed to conceive of the initial compliant implant and comprehend the envelope size. Further, a preliminary cadaveric wrist dissection, as illustrated in FIGs. 5C and 5D, was conducted to determine the size of the wrist capsule. These examples are provided for purposes of illustration only and are not intended to be limiting unless otherwise specified. Thus, the disclosure should in no way be construed as being limited to the following examples, but rather, should be construed to encompass any and all variations which become evident as a result of the teaching provided herein. Further, without further description, it is believed that one of ordinary skill in the art can, using the preceding description and the following illustrative examples, make and utilize the system and method of the present disclosure. The following working examples, therefore, specifically point out the embodiments of the present disclosure, and are not to be construed as limiting in any way the disclosure.

[0085] A patient population with pathologies resulting in the loss or excision of extensive bone in the carpal and distal radio-ulnar region was identified. These patients are ineligible for total wrist arthroplasty and can only undergo total wrist arthrodesis or reconstructive total wrist arthrodesis with a vascularized fibular graft. Although such a procedure prevents amputation, leaving the patient with a viable upper extremity, the functional disadvantages of a restrained wrist can be extensive. Observable outcomes, particularly in patients who lose the ability to pronate and supinate the forearm, include extreme shoulder compensation when conducting hand tasks, which may lead to additional joint-related pathologies.

[0086] Currently, the mean age for a primary wrist replacement is 60 years old. Even in the absence of particularly problematic pathological scenarios, wrist arthrodesis is the treatment of choice for young active patients, due to the instability of current implants. Moreover, these population appear to be more at risk for high-energy fractures of the wrist and giant cell tumors of the radius and carpal area (20-40 years), both of which result in extensive bone loss (or damage) that renders the use of conventional implants unfeasible. Patients who undergo wrist arthrodesis retain full hand function, but their wrist limitations leave them with a disability that negatively impacts their lifestyle and work from a young age.

[0087] Individuals with total wrist arthrodesis show difficulty conducting activities that require them to grip and hold objects with dexterity without the use of adaptive strategies. To assesssuch performance decrease, the Jebsen Hand Function Test is a commonly used instrument to evaluate hand function, which includes seven subtests assessing activities of daily living such as writing, picking up small objects, turning cards, pouring water, lifting heavy objects, moving large objects and stacking checkers. In patients subject to total arthrodesis, their ability to perform the subtests that require wrist mobility, such as lifting up small objects, writing, turning cards, and pouring water, may become significantly affected. Such difficulties are easily translatable to concrete limitations for work performance of patients employed in manual jobs were technology and adaptive strategies cannot overcome the hand hindered mobility.

[0088] The compliant implant is configured to provide patients, for whom the only alternative was total wrist arthrodesis, with the opportunity to preserve upper limb function without invalidating limitations. The implant is the result of a comprehensive re-engineering of the design strategy for joint prosthesis development. The objective was to recreate the biological joint's compliance while introducing inherent stability via a 2 DOF compliant implant, as opposed to recreating the wrist's articulating mechanism, which, in this case, is extremely complex and hardly reproducible.

[0089] The initial 2 DOF compliant implant design was subsequently generated and then optimized based on loading versus angle profile and an assumption of 1400 loaded cycles per day with a maximum resistive load of 221bs. Titanium (Ti6-A14v) was selected as the material of the compliant implant for the preliminary investigation and appeared to be suitable for withstanding the average wrist stresses while providing the advantages of titanium's extended fatigue life. Given the daily cycle requirements and the maximum loading condition, the compliant implant range of motion and mechanical design of the flexures were tuned to assure a 100-year fatigue lifespan for the compliant implant. This was confirmed by a finite element analysis that determined a Von Mises stress maximum of 482 MPa with respect to a calculated limit of 488 Mpa.

[0090] Two additional cadaveric dissections, as illustrated in FIGs. 5C and 5D, allowed for the validation of the selected anchoring method while providing information on wrist capsule dimensions fit. In the first alteration, surface and shape requirements for the implant were addressed while the efficacy of the range of motion was validated. Additionally, a cover for the deviation stage was included and tested as a device to prevent tissue impingement. The seconditeration of the innovation made it possible to determine the optimal envelope size and the compromises that a reduced range of motion could cause.

[0091] The disclosed compliant implant therefore represents a further validation of the disclosed implantable endoprosthesis over conventional implants. Taking into account the initial target pathologies and eligible patient pool, the first stage biomechanical and envelop dimension requirements have been optimally converted into a working prototype. As a result, the obtained implant has been subjected to a series of cadaveric dissection-based tests, as illustrated in FIGs. 5C and 5D, in which the envelope and anatomical interface design were optimized for the anticipated pathologically related conditions.

[0092] Embodiments disclosed herein may further relate to an example compression joint that is configured to achieve a single rotation with zero angular stiffness. FIGs. 7A-9E illustrate various views of an example implant 700 configured to rotate about an axis C along which a compressive or tensile force is applied. In one or more cases, the implant 700 may be used, for example, in a compliant stem for an orthopedic implant or endoprosthesis. The orthopedic implant or endoprosthesis may be used at joints such, for example, but not limited to, a knee, hip, ankle, elbow, shoulder, wrist, and the like.

[0093] In one or more cases, the implant 700 includes a joint 708 sized to rotate within a housing 706. The joint 708 may be configured to rotate about an axis C along which a compressive or tensile force is applied to a top portion 702 and / or bottom portion 704 of the implant 700. The housing 706 may have a rigid tubular body, in which the diameter of the tubular body is sized to receive a portion of the joint 708 therein. The implant 700 may be formed from one or more of the materials as described with respect to implant 100. Moreover, this disclosure, and features related to implant 700, incorporates the features of international publication number W02023 / 108094 by reference in its entirety.

[0094] In one or more cases, the joint 708 is formed in a cylindrical-like shape that includes groupings of flexures 710 and 712 that are disposed between a first end portion 718 and a second end portion 720 and extend along a length of a post 722. The first end portion 718 is a rigid member disposed at a top 702 of the joint 708. The first end portion 718 may include a plate 726 having a circular or rounded outer geometry with an exterior surface 724 and an interior surface 728. The plate 726 may include a through-hole 730 that is sized to allow a portion of the post 722 (e.g., a transverse end 736 of the post 722) to axially translate therethrough. In one or morecases, the through-hole 730 may be centrally positioned within the plate 726. The post 722 may include a rigid longitudinal body 738 disposed between the transverse end 736 and a radial end 734. In one or more cases, the transverse end 736 of the post 722 may include a shape sized to fit within the through-hole 730 of the plate 726. In one or more cases, the radial end 734 of the post 722 includes a plurality of rigid base members, such as base members 732a, 732b, and 732c. The base members 732a, 732b, and 732c may protrude outward from and be circumferentially disposed around the radial end 734 of the post 722. In one or more cases, the radial end 734 includes a body 740 disposed on an exterior surface of the radial end 734. The body 740 may be a rigid member that protrudes outwardly from the radial end 734. The body 740 may have a diameter that is less than the diameter of the body 738 of the post 722. In one or more cases, the body 740 may be used to align the base members 732a, 732b, and 732c with a preloaded plate 742. For example, the body 740 may be sized to be coupled with an alignment member 744 of the base plate 742. For instance, the body 740 may be sized to fit within a shape of the alignment member 744. In one or more cases, the diameter of the plate 726 may be larger than a diameter of the base members 732a, 732b, and 732c and / or the preloaded plate 750.

[0095] The flexures 710 and flexures 712 (e.g., flexures 712a and 712b) may extend in a longitudinal direction of the joint 708. In one or more cases, end portions 746 of the flexures 710 and 712 are coupled to the interior surface 728 of plate 726. End portions 748 of the flexures 710 may be coupled to interior surfaces of respective base members 732a, 732b, and 732c. End portions 749 of the flexures 712 may be coupled to respective portions of the preloaded plate 750. For instance, end portions 749 of flexures 712a and 712b may be coupled to members 752a of the preloaded plate 750. In some cases, the flexures 710 are positive stiffness flexures, and the flexures 712 are negative stiffness flexures. In one or more cases, the groupings of flexures 710, such as grouping 714, may be circumferentially disposed around a diameter of the joint 708. For example, the joint 708 may include three groupings of axisymmetric positive stiffness flexures. Flexures 712a and 712b may be referred to as a group and / or pairing 716 of flexures. In some cases, the grouping 716 may be circumferentially disposed around the diameter of the joint 708. For example, the joint 708 may include three groupings of axisymmetric negative stiffness flexures. In one or more cases, the groupings 714 of flexures 710 and the groupings 716 of flexures 712 may be intermittently disposed around the diameter of the joint 708, such that one grouping 714 of flexures 710 is positioned in between two groupings 716 of flexures 712, andvice versa. Although the example provided herein discusses three groupings 714 of flexures 710 and three groupings 716 of flexures 712, it should be understood that embodiments are contemplated in which the joint 708 includes less than three groupings 714 of flexures 710 and three groupings 716 of flexures 712 or more than three groupings 714 of flexures 710 and three groupings 716 of flexures 712. In one or more cases, the arrangement of groupings 714 and 716 of flexures 710 and 712 may provide a single rotation with minimal to zero angular stiffness if the implant 700 is compressed. As such, for the cases in which the implant 700, and in particular, the joint 708 is subjected to compression forces, the positive stiffness flexures, such as flexures 710, are in tension, and thus may not buckle.

[0096] In one or more cases, the implant 700 includes a preloaded plate 750 positioned at a bottom 704 of joint 708. The preloaded plate 750 may include a plurality of protruded members, such as members 752a, 752b, and 752c, that are circumferentially disposed around the preloaded plate 750. The members 752a, 752b, and 752c may be positioned on the preloaded plate 750 to interface with respective base members 732a, 732b, and 732c of post 722. For instance, the members 752a, 752b, and 752c may be positioned to interlock with base members 732a, 732b, and 732c. For example, base member 732a may be sized to fit within members 752b and 752a of plate 750. In one or more cases, plate 750 includes one or more holes, such as holes 754, and base members 732a, 732b, and 732c include one or more respective holes, such as holes 756. Holes 754 and 756 may be threaded or configured to receive a screw or bolt to fixedly and removably attach plate 750 to the one or more bases members 732a, 732b, and 732c, thereby coupling the members 752a, 752b, and 752c of plate 750 to bases members 732a, 732b, and 732c.

[0097] FIGs. 10A and 10B illustrate a process to preload the implant 700. To preload the implant 700, the plate 750 may be pushed in a direction towards the top 702 of the joint 708 until the plate 750 touches and interfaces with the base members 732a, 732b, and 732c. Subsequently, the plate 750 may be fastened to the base members 732a, 732b, and 732c, as described herein. Once the plate 750 is pushed up and fastened to the base members 732a, 732b, and 732c, the groupings 716 of flexures 712 (e.g., configured as axisymmetric negative stiffness flexures) may buckle inwards towards post 722. The flexures 712 may begin to exhibit the negative stiffness that cancels with the positive stiffness of the groupings 714 of flexures 710 (e.g., configured asaxisymmetric positive stiffness flexures). As such, the joint 708, and in particular, the entirety of the joint 708 may achieve zero stiffness.

[0098] FIG. HA illustrates the example compliant wrist implant 800 having proximal and distal anchors. FIG. 1 IB illustrates a cross-sectional view of wrist implant 800. The implant 800 includes one or more of the same or similar features as implant 100. As such, a description of such features is not repeated. FIGs. 11A and 1 IB illustrate the implant 800 as including a proximal anchor 104 and distal anchors 802, 804, and 806. Similar to implant 100, implant 800 includes a series arrangement of two orthogonal single cross-axis flexural pivots 808. One of the cross-axis flexural pivots 808 (e.g., flexure structures 114 and 118) corresponds to a flexion stage 810 (i.e., flexion / extension of the implant 800). The other of the cross-axis flexural pivots 808 (e.g., flexure structures 116) corresponds to a deviation stage 812 (i.e., radio / ulnar deviation). To prevent binding (i.e., when subjective to a compressive force (CF)) and enable smooth circumvention and dart-thrower motion, the axes of rotation of the flexion stage 810 (i.e., angular flexure displacement (AFD)) and the deviation stage 812 (i.e., angular deviation displacement (ADD)) are positioned so the flexure structures intersect orthogonally on the same plane. Because the wrist joint operates only in compression (CF), each x-pivot is inverted such that the flexural elements are only subjected to tension when the wrist is in compression to prevent buckling of the thin flexure blades. Similar to that of implant 100, the implant 800 may additionally feature a cover to protect the surrounding soft tissues from the metal blades and hardstops that protect the implant 800 from over-rotation.

[0099] The first joint member 106, second joint member 108, third joint member 110, and fourth joint member 112 of implant 800 may further include structural supports disposed on the walls of the respective joint members. For example joint member 106 may include structural supports 814 that protrude towards one another from the walls 813 of the joint member 106. In another examplejoint member 110 may include structural supports 816 that protrude towards one another from the walls 815 of the joint member 110. The structural supports may provide increased rigidity to the walls of the respective joint member.

[0100] Implant 800 may be implanted with a radial and carpal fixation to a wrist 400, as illustrated in FIGs. 12A and 12B, in a same or similar manner as implant 100. In one or more cases, the implant 800 may be anchored, via anchor 104, to bone, such as the radius, using for example, a radius intermedullary fixation with a press-fit, cemented, or compression-style radialstem. In one or more cases, intraosseous rods or pins may also be used to fixate the implant 800 or anchors of the implant 800 to cancellous bone. At the carpal region of the wrist 400, a carpal plate, such as the crossmember 138 of the implant 800 may be attached to the distal carpal row of the wrist 400. The crossmember 138 may be attached to the carpal row via a central stem, such as anchor 802, through the capitate. Additionally, fasteners 804 and 806 may be attached to the crossmember 138 and one or both of the carpal row and metacarpals of the wrist 400. For example, fastener 806 may attach the implant 800 to the wrist 400 via the trapezoid and second metacarpal, and fastener 804 may attach the implant 800 to the wrist 400 via the hamate and fourth metacarpal or the hamate alone. In one or more cases, one or more portions of the crossmember 138, anchor 802, and / or fasteners 804 and 806 may be coated with hydroxyapatite or another porous material to promote bone growth and integration in this area, which is prone to loosening.

[0101] In an effort to validate the feasibility and viability of the implant 800, alternative implant to total wrist fusion for patients with extensive bone damage and loss, experimental examples were performed to conceive of the initial compliant implant and comprehend the envelope size. These examples are provided for purposes of illustration only and are not intended to be limiting unless otherwise specified. Thus, the disclosure should in no way be construed as being limited to the following examples, but rather, should be construed to encompass any and all variations which become evident as a result of the teaching provided herein. Further, without further description, it is believed that one of ordinary skill in the art can, using the preceding description and the following illustrative examples, make and utilize the system and method of the present disclosure. The following working examples, therefore, specifically point out the embodiments of the present disclosure, and are not to be construed as limiting in any way the disclosure.

[0102] Fitting the implant within the anatomical constraints of the joint capsule without creating excessive tension was addressed by a preliminary cadaveric dissection which defined the envelope dimensions: Height 47 mm, width 49 mm, depth 25 mm, as illustrated in FIG. 13. The method closely mirrors typical arthroplasty techniques, but with the minor adjustment of more extensive removal of the distal radius and ulna. More specifically, the space was created by a standard excision of the proximal carpal row, transecting the distal carpal row proximally to the hamate hook and resecting 30 mm of the radius head. Furthermore, a Darrach's procedure involves the removal of the distal end of the ulna. Given that patients who would meet the initialcriteria for the implant have either experienced significant bone loss or have non-viable bony structures due to giant cell tumor or high energy fractures, a Darrach’s procedure was performed. In these instances, an extended resection would already be indicated. In order to preserve the interosseous membrane that stabilizes the forearm, the resection is constrained within 30 mm of the forearm bone heads. This approach guarantees a secure fit of the implant while reducing the likelihood of complications after the surgery.

[0103] Titanium Grade 5 (e.g., Ti6A14V) was selected for its excellent mechanical properties and biocompatibility. This material can withstand the stresses of daily wrist movements while providing a long fatigue life, essential for the implant's durability. The ideal lifespan of the implant is expected to be 100 years, equivalent to about 1400 loading cycles per day. The design process ensured that the maximum Von Mises stress remained within the safe limit of 488 MPa, excluding friction wear as the x-pivot relies on bending rather than rubbing or sliding. Overall, the choice of titanium grade 5 allows maintaining a balance between flexibility and strength while providing reliable performance and durability in the human body.

[0104] The experiment herein targeted resistive forces or loads on the wrist. For example, as illustrated in FIG. 13, in accordance with the resistive load of 100N at the fingers, 600N of compressive force at the wrist joint was considered. However, such a load of about 22 lbs may cause higher peaks during ulnar deviation.

[0105] Based on this information, the flexural elements were refined through a series of simulation studies while remaining within the defined envelope dimensions of the implant. Initially, a machine learning algorithm, trained with finite element analysis (FEA) data on a single degree of freedom (DOF) x-pivot, provided the foundation for defining the design space. Several parameters such as blade length, blade width, blade angle, and the variable thickness ratio, were employed to dimension the flexural elements. By locking certain parameters and adjusting others, a semi-optimal configuration for the flexures was identified. In a single-DOF system, a grounded base and a rotating stage experience an inverted compressive load that keeps the x-pivot compressed throughout its range of motion.

[0106] However, as the design incorporated two nested DOF stages, additional considerations became necessary, specifically, additional considerations included off-axis loads, which arose from the combined movement of both stages, and the resulting stress distribution across the flexural structure. Although the same parameters were used for flexure design, the complexityintroduced by the two DOF stages required a more nuanced optimization. To address these complexities, the implant was manually refined through detailed FEA simulations using ABAQUS. Quadratic tetrahedron meshing and adaptive mesh refinement techniques were employed to ensure the results converged appropriately. Given the risks of lateral or local buckling of the flexural elements due to these off-axis loads, the Riks solver was utilized instead of static general to accurately capture the non-linear behavior of the structure under varying loads. This methodological approach enabled the development of a robust proof-of-concept wrist implant capable of withstanding the complex loading conditions encountered in real-world wrist functionality.

[0107] The initial implant design was 3D printed as a unibody in carbon fiber-reinforced nylon. The prototype was intended for early cadaveric validation, to refine the implant envelope dimensions and anatomical fit. The material was later switched to Ti6A14V, moving into the functional validation phase. As described herein, the mechanical properties of titanium, namely fatigue resistance and biocompatibility make this material an ideal material for the high loads and cycles that the wrist implant would have to undergo. However, the compact design, with two orthogonally nested x-pivot configurations, makes the envelope rather complex. A high precision, fully functional prototype could not be manufactured as a unibody due to the complicated internal mechanism and parts crossover, which prevent easy access to critical components.

[0108] Although selective laser sintering (SLS) may give some preliminary results, SLS lacks the accuracy required to reproduce the flexure's curvature and thin sections, especially those less than 0.3 mm thickness. In such sections, the risk of cooling warping makes maintaining desired mechanical properties difficult and quality control unreliable. To overcome these manufacturing limitations the implant was restructured into 7 modular envelope components and 7 independent flexures. This modular approach allows more precise part fabrication via CNC machining, for the envelope components, and wire EDM, for the flexures. The approach facilitates manufacture while making assembly, adjustments, and repairs much simpler. During the prototyping and bench testing phases, individual component issues were able to be isolated and addressed with the modular implant design. Additionally, this strategy enhanced the implant's long-term performance and made the implant more flexible to future modifications or improvements without a complete redesign.

[0109] Given the high precision required for the flexural elements and the overall implant assembly, Geometric Dimensioning and Tolerancing (GD&T) specifications are critical. Close tolerances ensure that every modular component of the envelope fits together precisely and there is no "wiggle" between parts which could cause parasitic motions or degraded performance. These tolerances are particularly important for validation of performance of flexural elements as even small deviations could compromise the stability and function of the whole system. Additionally, with GD&T, manufacturing is standardized to have consistency and repeatability across multiple production runs. Ultimately, the modular design and the strict GD&T guidelines controlled manufacturing to ensure the implant would meet functional and performance requirements. This strategy allows better quality control, faster prototyping, and flexibility to refine design further during functional testing and eventual clinical validation.

[0110] A compliant wrist implant prototype was fabricated from Ti6A14V for experimental validation. The seven envelope components of the implant were machined by HLH Prototypes (PRC), while the seven flexures were produced by Absolute Wire EDM (USA) using wire EDM technology. Due to the modular design of the implant, the radial and carpal components were replaced with attachments tailored for bench testing. The primary aim of this testing was to evaluate the unloaded and loaded stiffness profiles of the implant during flexion / extension, radio / ulnar deviation, and dart-thrower motion.

[0111] For unloaded stiffness measurements, the radial stage of the implant was secured orthogonally to a vertical optical plate using an M3 bolt. On the carpal stage, weights ranging from 5 to 250 grams, in 5-gram increments, were attached via an M3 bolt until the full range of motion was reached. A static camera, fixed in position throughout the experiment, captured images for each weight. The captured images were subsequently processed in Adobe Illustrator to assess the angle of displacement relative to the neutral position for each load, allowing for the calculation of torque.

[0112] For the loaded stiffness evaluation, the implant was mounted on one end to the flange of a 6-DOF industrial manipulator (KUKA), while the opposite end was anchored to a grounded base. Loading was applied in two stages: first, a tensile load was introduced, followed by a 12- degree rotation of the end effector around the axis of flexion / extension, radio / ulnar deviation, or dart-thrower motion.

[0113] The end effector was then returned to the neutral position before being rotated back into negative twelve degrees. Stiffness during flexion / extension and radio / ulnar deviation was tested at loads of 250N, 300N, 400N, 500N, and 600N, while dart-thrower motion was tested at 250N and 300N only. Imperfections in the manufacturing process caused minimal rubbing between the internal stages of the implant and the walls of the case under high loads or during dart-throwing motion. Nevertheless, the modular design of the implant allowed for post-processing of the parts to eliminate this interference. Out of abundance of caution, the implant was tested at 80% of its maximum range of motion to prevent damage to the one of one prototype.

[0114] The surgical technique for the compliant wrist arthroplasty follows a standard dorsal approach, similar to that used for conventional wrist arthroplasties. However, due to the specific anatomical considerations of the target patient population and the implant dimensions, an increased level of bone resection is necessary to ensure proper implant fit and stability without compromising vital anatomical structures. One critical aspect is to remain proximal to the hamate hook to safeguard the ulnar nerve. Compromising this nerve can lead to sensory or motor deficits, causing ulnar neuropathy and significantly affecting hand function. Furthermore, limiting the resection of the ulnar head and distal radius to preserve the forearm interosseous membrane is essential for maintaining forearm stability and function. Extending the resection beyond this boundary risks destabilization and could compromise pronation and supination movements due to damage to the interosseous membrane.

[0115] The procedure begins with the patient’s hand and forearm positioned supine, followed by a longitudinal dorsal incision extending from the distal radius to the base of the third metacarpal. Skin and subcutaneous tissues are dissected to expose the extensor retinaculum, which is then incised to reveal the underlying joint capsule. The extensor tendons, namely the extensor carpi radialis longus, extensor carpi radialis brevis, and extensor carpi ulnaris, are retracted laterally to facilitate access to the joint. The proximal carpal row is addressed first after reflecting the extensor compartments. The scaphoid, lunate, and triquetrum are excised using rongeurs and a micro sagittal saw to perform a complete proximal row carpectomy. This resection provides part of the space for the implant while preserving the stability of the distal carpal row, which is then transected with a 40 mm horizontal cut just proximal to the hamate hook.

[0116] After the excision of the carpal bones, the dorsal incision is extended proximally to expose approximately 30 mm of the radial head, which is then resected, while ensuring theresection remains distal to the forearm interosseous membrane. A Darrach’s procedure is performed next, resecting 25 mm of the ulnar head slightly distal to the radial resection. The total resected area, validated in a sample cadaver, measures 47 mm in height, 49 mm in width, and 25 mm in depth, providing sufficient space for the implant.

[0117] Following bone resection, the radius is prepared to accommodate the modular stem. The radial bone is drilled, and the tapered radial stem is cemented into the prepared cavity. The carpal plate is fitted next by drilling a central tight clearance hole into the capitate. A 38 mm screw is used to fix the plate to the second metacarpal at a 100-degree inclination relative to the orthogonal plane of the plate. An additional 17 mm screw is inserted into the hamate at a mirrored inclination to ensure secure fixation and appropriate load distribution. Intraoperative fluoroscopy is utilized to verify proper alignment and ensure smooth joint articulation without impingement.

[0118] Once the implant's position is confirmed, the joint capsule is closed using interrupted sutures to restore soft tissue integrity. The extensor tendons are repositioned over the joint, and the extensor retinaculum is meticulously repaired to allow smooth tendon gliding without restriction. The skin is then closed with interrupted sutures. This technique ensures secure and functional implantation, with bone resection tailored to accommodate the prosthesis while safeguarding critical anatomical structures.

[0119] A motion capture setup with six Vicon Vantage cameras was used to test the motion of the implanted wrist. A cadaver forearm was fixed, on an operating table, at a 45-degree angle relative to the horizontal plane. The cameras were pointed to capture data from the dorsal aspect of the hand. Marker placement on the cadaver's hand, wrist, and forearm allowed movement tracking during simulated flexion / extension, radio / ulnar deviation, and dart-throwing motions. These motions were induced manually with a rigid handle attached to a plate used to keep the palm open and extended during the procedure.

[0120] The data acquisition process was performed in two stages for accurate comparison and scaling. The first trial recorded the natural range of motion of the intact biological wrist. The second trial recorded data after arthroplasty. The motion data was processed and collected during both trials using OpenSim. This allowed for detailed analysis of the wrist’s range of motion across different planes, providing quantitative insights into the performance of the biological wrist compared to the implanted prosthesis.

[0121] In the finite element analysis (FEA), the mechanical performance of wrist implant flexural elements was investigated under different loading conditions. Key findings have been obtained from parameter sensitivity studies focusing on blade design parameters such as thickness and length ratio, which are crucial to implant functionality and durability. The findings included optimal blade parameters that minimize stress while maximizing mechanical efficiency. The optimal thickness-length ratio was between 0.2 and 0.3, in which stress on the implant’s most challenging motion is minimized, thereby reducing the mechanical failure risk. In an effort to first optimize for flexion / extension and deviation, the chosen parameter is 0.75. Blade thickness also influences the structural integrity of the implant. 0.3 mm blade thickness was found to be the optimal balance between flexibility and durability. Deviations from this thickness significantly affect stress levels.

[0122] Additionally, the FEA results have guided the refinement of other design parameters, such as the variable thickness ratio and the thickness length ratio. Adjustments in such parameters aim at optimizing the load-bearing capability of the implant without compromising its flexibility needed for joint movement. The convergence of FEA results has confirmed the robustness of the implant design under simulated physiological loads. In the semi -optimized flexural element configuration, the blade length is 31 mm, the blade width is 5.25 mm, the blade angle is 16 degrees, the blade thickness is 0.3 mm, the variable thickness ratio is 4, and the thickness length ratio is 0.75. Under this configuration, each single degree of freedom simulated independently reached a maximum of Von Mises stress of 440 MPa for 15 degrees of rotation in a single direction with 600N of compressive load.

[0123] When analyzing the behavior of the nested DOF stages assembled in the envelope, the FEA revealed localized stress concentrations in areas bearing off-axis loads, as illustrated in FIGs. 14A-14C. The stresses remained however close to acceptable limits, and no significant parasitic motion or buckling was detected in the flexural elements in single-degree actuation. Max Von Mises stress at 15 degrees of rotation for flexion / extension is 495 MPa. A reduction of one degree applied to the deviation side shows that the maximum Von Mises stress remains well within the 488 MPa limit for 100 years of fatigue life. However, the two-stage design complexity resulted in higher stress deformation in the flexural elements during lateral loading and parasitic lateral displacement of the flexion stage. Therefore, for the dart-throwing motion, the limit of 488 MPa was reached at 283 N compressive load.

[0124] In the unloaded stiffness test, the torque-angular displacement relationship over the range of motion of the wrist implant was investigated, as illustrated in FIG. 15. The maximum effective rotation in one direction for flexion / extension was 14 degrees, and for radio / ulnar deviation, maximum effective rotation was 13.75 degrees. The stiffness profiles of these movements coincide closely and show near-exponential torque growth, slightly different from the linear trend predicted by FEA. This deviation is mostly pronounced between 5 and 10 degrees, where the observed torque is somewhat lower than expected. The maximum torque required to obtain these maximal displacements is 0.072 Nm in flexion / extension and 0.069 Nm in radio / ulnar deviation, respectively. For the dart-throwing motion, involving simultaneous actuation of both mechanisms, the non-linearity of the stiffness curve is more pronounced, suggesting a lower overall stiffness up to approximately 15 degrees of rotation. Here the range is 20.62 degrees with corresponding peak torque of 0.109 Nm, showing greater flexibility in composite motion rather than in isolated movements.

[0125] In the Kuka-driven loaded stiffness tests, for each degree of freedom and composite motion, a full rotational cycle including positive and negative rotations was carried out. The graph plots a continuous cycle of ten range repetitions for each motion and loading condition. For flexion / extension, the maximum tested range was conservatively 24 degrees, shy of the effective maximum of 28 degrees. Here, the stiffness increased linearly with load. At 250N minimum load setting, the maximum torque was between -0.14 and 0.15 Nm, in the positive and negative ranges, respectively. For radio / ulnar deviation, the maximum tested range was 21.76 degrees under the effective maximum of 27.5 degrees. This cautious approach was taken to avoid excessive lateral loads on the nested flexion mechanism. A similar linear stiffness trend was observed with increasing load. The maximum torque at 250N was -0.11 to 0.12 Nm, and at 600N from -0.45 to 0.43 Nm in both positive and negative directions. These trajectories had overlapping patterns and negligible deviations. A zero-point shift with increasing load is likely caused by small manufacturing imperfections and mainly by the structural stiffness of the manipulator, which cannot compensate for its linkage deformation underload. For the dartthrowing motion only two loading conditions were tested: 250N and 300N. The maximum torque varied between -0.11 and 0.11 Nm at 250N and -0.32 to 0.17 Nm at 300N, with a tested range of 22 degrees, below the effective maximum of 41.2 degrees. The composite motion showed a typical hysteretic behavior, with a higher peak torque on the negative end. Despite theseobservations, no contact or significant parasitic motions were detected during testing. The distinctive behavior observed in the dart-throwing motion, as evidenced by the hysteresis and peak torque discrepancies, may be attributed to the complex interaction between the flexion / extension and radio / ulnar deviation mechanisms under load. This interaction likely results in uneven stress distributions and dynamic responses that are not as prevalent in the simpler, single-movement tests.

[0126] The cadaveric dissection-based test yielded important information regarding the implant anatomical fit and functional performance. The surgery confirmed that the radial stem could be implanted within the intermedullary canal and carpal fixation at the second metacarpal was successful. Post-surgical observations noted that the implant accommodated within the wrist capsule seamlessly, allowing the skin to be closed without inducing any rigidity, thereby preserving the natural fluidity of wrist motions. Motion capture analysis determined the range of motion and allowed a comparison to biological wrist capabilities. For example, flexion / extension of implanted wrist was 21.5 degrees in contrast to 48 degrees in a cadaver's biological wrist. Radio-ulnar deviation was 41.23 degrees compared to 109.2 degrees in the natural state. The dart-throwing motion was 35.03 degrees compared with 57 degrees in the biological wrist, indicating a moderate reduction in range but maintaining substantial functional movement. Motion capture data also indicated that the axis of rotation of the implanted wrist was approximately identical to the natural wrist with only a minor offset. Notably, the dart-throwing motion of the implant matched that of the original wrist, with only a 0.45 degree offset between the principal axes and a 20 degrees positive bias in flexion indicating a slight biomechanical change in the wrist's behavior.

[0127] The embodiments of the novel compliant wrist implant as provided herein enhance loadbearing capabilities and durability, offering a robust and functional alternative to wrist fusion for patients with extensive bone loss. The embodiments provided herein successfully integrate two complementary x-pivot mechanisms to facilitate fluid motion that closely replicates biological wrist movement. FEA was employed to refine the design, allowing the anticipation of potential mechanical failures and ensuring that the implant's behavior aligned with theoretical predictions. A modular prototype using Ti6A14V was manufactured and subsequently verified through both bench-top and cadaveric testing.

[0128] FEA provided the basis for defining a semi-optimal design space for the compliant wrist implant. With Abaqus-aided modeling, the flexural elements' configurations were identified and optimized for resistance to lateral stresses, an inherent challenge of the nested design. The embodiments provided herein optimized the parameters for a single mechanism, incrementally increasing the orthogonal moment of inertia, for the blades of the other mechanism, by adjusting each flexure base thickness and slope. This adjustment was also critical for limiting the lateral load effects of the composite movement of the nested mechanisms. At the center of the blade, manipulating the minimum thickness, to an optimal dimension of 0.3 mm, resulted in a significant reduction of stress. This allowed for the complex biomechanical loading of the wrist within constrained envelope dimensions while preserving a viable range of motion.

[0129] Manufacturing presented substantial challenges, particularly in achieving precision without compromising the implant’s integrity. The complexity of the nested mechanisms made machining a unibody implant impractical. Switching to a modular design provided optimal manufacturability. Additionally, by implementing GD&T standards, reliable assimilability was achieved. Such an approach ensured that the prototype behavior was consistent with FEA predictions. Bench-top testing confirmed range of motion and mechanical behavior of the implant under different loads. Stiffness measurements revealed a gradual increase with loading, though the values remained relatively low, indicating minimal resistance to motion. Hence, this suggests the implant allows natural wrist movement without significant mechanical limitation. In addition, the experimental tests showed that variations in the titanium's elastic modulus, possibly due to the wire EDM recast layer or material property fluctuations, slightly increased the horizontal displacement of the x-pivot center of rotation and decreased the total range of motion due to the envelope mechanical stops.

[0130] Clinically, the implant demonstrated excellent integration within the wrist capsule. Cadaveric testing revealed an adequate fit and demonstrated the implant's compatibility with surrounding soft tissues, which likely contributed to an increased range of motion. While biomechanical testing revealed some range limitations, ex-vivo motion capture revealed considerable functional capability. The implant achieved 35.03 degrees in dart-throwing compared to the biological wrist, which achieved 57 degrees in motion. Post arthroplasty assessments showed that the hand moved naturally without binding or impingement. Additionally, the mechanical stops are engaged precisely at the range extremes, ensuring stabilityand the ability to bear high loads at critical points, a fundamental factor for long-term implant reliability.

[0131] The various embodiments described above are provided by way of illustration only and should not be construed to limit the claims attached hereto. Those skilled in the art will readily recognize various modifications and changes that may be made without following the example embodiments and applications illustrated and described herein, and without departing from the spirit and scope of the following claims.

Claims

CLAIMSWhat is claimed is:

1. An orthopedic device, comprising: a first joint member having a hollow body sized to receive a portion of a second joint member therein; the second joint member being positioned in between and arranged in series with a third joint member and a fourth joint member; and the third joint member and fourth joint member being positioned on opposite ends of a crossmember, wherein a first flexure structure flexibly couples together the first joint member and the second joint member, wherein a second flexure structure flexibly couples together the second joint member and the third joint member, wherein a third flexure structure flexibly couples together the second joint member and the fourth joint member, wherein the first joint member, third joint member, and fourth joint member are configured to rotate about the second joint member within two degrees of freedom.

2. The orthopedic device of claim 1, wherein at least a portion of the second flexure structure resides within a hollow body of the third joint member.

3. The orthopedic device of claim 2, wherein the second flexure structure comprises a first end and second end disposed on opposite ends of at least one flexure, wherein the first end comprises a rigid body coupled to an exterior surface of the second joint member, and wherein the second end is flexibly coupled to an interior surface of the hollow body of the third joint member.

4. The orthopedic device of claim 3, wherein the hollow body of the third joint member comprises a range-limiting area having at least one surface shaped to interface with anopposing surface of the rigid body of the second flexure structure to define an end of a range of motion of the rigid body within the third joint member.

5. The orthopedic device of claim 4, wherein the at least one surface of the rangelimiting area is configured to prevent a portion of the second flexure structure from articulating in one or both of a lateral direction and a vertical direction.

6. The orthopedic device of claim 3, wherein the second flexure structure comprises two flexures oriented in a crossing pattern within the hollow body of the third joint member.

7. The orthopedic device of claim 1, wherein the second joint member comprises a hollow body sized to receive a portion of the first joint member therein.

8. The orthopedic device of claim 7, wherein the first flexure structure comprises a first end and a second end, and wherein the first end of the first flexure structure is coupled to an interior surface of an end the first joint member that is configured to rotate within the second joint member.

9. The orthopedic device of claim 8, wherein the second end of the first flexure structure is coupled to an interior surface of an end the second joint member that is configured to rotate within the first joint member.

10. The orthopedic device of claim 1, further comprising a first anchor extending outward from an exterior surface of the first joint member, and one or more second anchors extending outward from a portion of the crossmember.

11. The orthopedic device of claim 10, wherein a surface of the crossmember that includes the one or more second anchors is formed or coated with a biocompatible material.

12. An orthopedic device, comprising: a housing having a hollow body; anda compression joint, a portion of which is sized and configured to rotate within the housing about an axis along which a force is applied to the orthopedic device, wherein the joint comprises groupings of positive stiffness flexures and groupings of negative stiffness flexures disposed between a first end portion and a second end portion of the joint, the groupings of positive stiffness flexures and groupings of negative stiffness flexures being circumferentially and intermittently disposed around the joint, and wherein an arrangement of the groupings of positive stiffness flexures is configured to negate stiffness exhibited by the groupings of negative stiffness flexures in a preloaded state.

13. The orthopedic device of claim 12, wherein: the joint comprises a post having a longitudinal body disposed between a transverse end and a radial end; the first end portion comprises a plate having a through-hole configured to receive the transverse end of the post therein, and the groupings of positive stiffness flexures and groupings of negative stiffness flexures are coupled to an interior surface of the plate, and the second end portion comprising a plurality of base members that protrude outward from and are circumferentially disposed around the radial end of the post.

14. The orthopedic device of claim 13, wherein one end of the groupings of positive stiffness flexures and groupings of negative stiffness flexures are coupled to an interior surface of the plate of the first end portion, and wherein an opposite end of the groupings of positive stiffness flexures and groupings of negative stiffness flexures are coupled to an interior surface of the base members.

15. The orthopedic device of claim 13, wherein the second end portion further comprises a second plate comprising a plurality of protruded members that extend from and are circumferentially disposed around a surface of the second plate.

16. The orthopedic device of claim 15, wherein the protruded members are positioned on the second plate to interlock with the base members of the post.

17. The orthopedic device of claim 15, wherein the second plate is coupled with base members to preload the joint.

18. The orthopedic device of claim 15, wherein the post comprises a first alignment member sized to interface with a shape of a second alignment member of the second plate.

19. The orthopedic device of claim 12, wherein a grouping of negative stiffness flexures comprises two negative stiffness flexures.

20. The orthopedic device of claim 12, wherein the joint comprises three groupings of positive stiffness flexures and three groupings of negative stiffness flexures.

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