INTERPHALANGEAL JOINT IMPLANT

Abstract

The present disclosure provides a joint implant for replacing a finger joint. The joint implant includes a first component, wherein the first component includes a first joint section and a first anchoring section, the first joint section including a concave joint surface about a first axis and the first anchoring section extending transverse to the first axis. The joint implant also includes a second component, wherein the second component includes a second joint section and a second anchoring section, the second joint section including a circumferential surface about a second axis and the second anchoring section extending transverse to the second axis, wherein the circumferential surface includes a convex joint surface that is configured to act as a hinge joint with the concave joint surface of the first joint section.

Claims

1. A joint implant configured to replace for replacing an interphalangeal joint, comprising: a first component, wherein the first component comprises a first joint section and a first anchoring section, the first joint section including a concave joint surface about a first axis and the first anchoring section extending transverse to the first axis; a second component, wherein the second component comprises a second joint section and a second anchoring section, the second joint section including a circumferential surface about a second axis and the second anchoring section extending transverse to the second axis, wherein the circumferential surface comprises a convex joint surface that is configured to act as a hinge joint with the concave joint surface of the first joint section; the second component further comprising a bone shield arranged between the second joint section and the second anchoring section, wherein the bone shield extends about a third axis and partially covers the circumferential surface of the second joint section with a gap being formed between the circumferential surface and the bone shield.

2. The joint implant according to claim 1, wherein the second joint section is connected to the bone shield via a compensation mechanism, the compensation mechanism configured to allow a relative movement between the second joint section and the bone shield in relation to a fourth axis, the fourth axis being transverse to the second axis of the second joint section.

3. The joint implant according to claim 2, wherein the compensation mechanism comprises a pin and a hole, wherein the pin and the hole are configured for a relative movement along and/or about the fourth axis (A4).

4. The joint implant according to claim 1, wherein the gap is formed between the circumferential surface of the second joint section and an inner surface of the bone shield by a difference in their profiles.

5. The joint implant according to claim 1, wherein the profile of the circumferential surface in a cross-section along the second axis is faceted.

6. The joint implant according to claim 1, wherein along the second axis, the convex joint surface is arranged in a middle portion and in between two tapered sections of the circumferential surface, wherein the tapered sections are configured to limit the relative rotation of the bone shield and the second joint section about the fourth axis.

7. The joint implant according to claim 6, wherein the relative rotation of the bone shield and the second joint section about the fourth axis is limited to about ±2° to ±10°.

8. The joint implant of claim 1, wherein the bone shield forms at least one abutment surface facing in a circumferential direction in relation to the third axis, wherein the bond shield is configured to limit flexion or extension of the joint implant.

9. The joint implant of claim 1, wherein the range of motion of the joint implant in flexion-extension is approximately 90° to 110°.

10. The joint implant according to claim 1, wherein the first joint section comprises, on each side of the concave joint surface along the first axis, a support face extending transverse to the first axis, each support face including a retaining pin protruding from the support face, and wherein the second joint section comprises, on each side of the circumferential surface, an end face extending transverse to the second axis, wherein in each end face a retaining groove is formed between the center of the end face up to the circumferential surface, the retaining grooves extending at an angle to the radial direction relative to the second axis.

11. The joint implant according to claim 1, wherein the first anchoring section and/or the second anchoring section has a plate shape, the surface of the plate having a surface structure with protrusions and/or recesses, wherein the protrusions and/or recessed are oriented in the direction of the first and second axes.

12. The joint implant according to claim 1, wherein the first anchoring section and/or the second anchoring section has a plasma coating.

13. The joint implant according to claim 1, wherein the first joint section, the first anchoring section and/or the second anchoring section is made of a metal alloy, and the second joint section is made of a material selected from the group consisting of a metal alloy, a polymer, and UHMWPE.

14. A method for assembling a joint implant for replacing an interphalangeal joint, comprising the steps: providing a first joint section, the first joint section comprising a concave joint surface about a first joint axis; providing a second joint section, the second joint section comprising a circumferential surface including a convex joint surface about a second joint axis; bringing the first joint axis and the second joint axis substantially into alignment; and bringing the convex joint surface into contact with the concave joint surface for forming a hinge joint.

15. The method according to claim 14, wherein for bringing the first joint axis and the second joint axis substantially into alignment, retaining grooves in the end faces of the second joint section are brought into engagement with corresponding retaining pins of the first joint section; and for bringing the convex joint surface into contact with the concave joint surface, the first joint section and the second joint section are rotated relative to each other after the retaining pins and retaining grooves are engaged until the concave joint surface faces the convex joint surface.

Description

SHORT DESCRIPTION OF THE DRAWINGS

[0098] The following figures illustrate preferred embodiments of the present invention. These embodiments are not to be construed as limiting but merely for enhancing the understanding of the invention in context with the following description. In these figures, same reference signs refer to features throughout the drawings that have the same or an equivalent function and/or structure. It is to be noted that a repetitive description of these features is generally omitted for reasons of conciseness.

[0099] FIG. 1 is a three-dimensional view illustrating an embodiment of an assembled interphalangeal joint implant in extension according to the present disclosure;

[0100] FIG. 2 is a schematic drawing for illustrating the kinematics of an interphalangeal joints of a hand;

[0101] FIG. 3 is a three-dimensional view illustrating the embodiment of the assembled interphalangeal joint implant of FIG. 1 in flexion;

[0102] FIG. 4 is a three-dimensional view of the interphalangeal joint implant in a partly assembled state;

[0103] FIG. 5 is three-dimensional exploded view of an interphalangeal joint implant for illustrating an embodiment of a compensatory mechanism; and

[0104] FIG. 6 is a three-dimension exploded view for showing an assembly of a first and a second joint section in more detail.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0105] In the following, preferred embodiments of an interphalangeal joint implant according to the present disclosure are described under reference to the figures. FIG. 1 illustrates a three-dimensional view of an assembled joint implant for replacing an interphalangeal joint in a finger or foot of a patient.

[0106] The joint implant is configured to be inserted from a lateral or medial side into a space created by resecting an interphalangeal joint. For example, FIG. 2 shows a schematic cross-section of a finger.

[0107] The interphalangeal joints are located between any of two adjacent bones of this finger. In case of the finger illustrated in FIG. 2, these interphalangeal joints are the distal interphalangeal joint (DIP), the proximal interphalangeal joint (PIP), and the metacarpophalangeal joint (MCP).

[0108] As the skilled person will appreciate, the interphalangeal joints of the foot have a similar configuration. A joint implant according to the present disclosure is inserted laterally, i.e. from the lateral or medial side of an interphalangeal joint that has previously been resected. For example, under reference to FIG. 2, the joint implant is inserted in a direction substantially perpendicular to the plane of this figure.

[0109] Returning to FIG. 1, the joint implant is generally configured as a hinge joint. However, as will be explained in the following, this hinge joint has a configuration that also allows for comparatively small movements in rotational (supination/pronation) and/or translational directions (compression/distraction) in order to enhance the adaption of the interphalangeal joint replacement to the kinematic environment of a patient. This kinematic environment is, for example, defined by the arrangement of tendons and muscles. As a result, the interphalangeal joint functions similar to the native joint to be replaced.

[0110] The hinge joint illustrated in FIG. 1 comprises a first component 1 and a second component 2. The first component 1 and the second component 2 function as hinge joint, i.e. they rotate relative to each other about a hinge axis (first axis A1 and second axis A2 that are basically aligned during contact of the concave joint surface 21 and the convex joint surface 41).

[0111] The illustration of the exemplary joint implant according to this disclosure in FIG. 1 shows the joint implant in extension. For comparison, FIG. 3 shows the joint implant of FIG. 1 at rotational position in flexion at about 105°. The angular range between extension and maximum flexion defines the range of motion of the interphalangeal joint implant. Preferably, the range of motion of such a joint implant is 0° to 110°, preferably 0° to 100°, or 0° to 90°.

[0112] Even more preferably, these ranges of motion start from an angle larger than 0°, i.e. an angle slightly larger than the angle of complete extension (at 0°) . For example, the range of motion may start at an angle of 1°, 2°, 5°, or 10°. This serves to prevent an overextension of the finger joint implant.

[0113] As illustrated in FIG. 1, the first (preferably proximal) component 1 comprises a first anchoring section 10 and a first joint section 20. The second (preferably distal) component 2 comprises a second anchoring section 30 and a second joint section 40 (see FIGS. 3 and 4).

[0114] The anchoring section 10 of the first component 1 is preferably integrally formed with the first joint section 20.

[0115] In other words, the first anchoring section 10 and the first joint section 20 are connected by a material bond (e.g. by welding, soldering, bonding, etc.) or are fabricated as one-piece (e.g. by casting, sintering, 3D-printing, etc.).

[0116] As described above, the second component 2 comprises a joint section 40 and an anchoring section 30. A bone shield 60 is arranged between the joint section 40 and the anchoring section 30.

[0117] As described above, the anchoring section 30 and the bone shield 60 are preferably integrally formed. The same may apply to the connection between the bone shield 60 and the second joint section 40.

[0118] However, the bone shield 60 and the second joint section 40 are, as illustrated, preferably connected by a compensation mechanism 50 that allows for a translational and/or rotational movability between these two components as will be described further below in more detail.

[0119] One of the advantages of a joint implant according to the present disclosure is the insertion of this joint implant from a lateral or medial side of an interphalangeal joint.

[0120] As illustrated for the exemplary embodiment of a joint implant in FIG. 1, the anchoring sections 10, 30 preferably have a plate shape.

[0121] Further, any one or both of the anchoring sections 10, 30 may be formed with at least one major surface (i.e. larger surface of the anchoring section) having a structure. The structured surface may be structured on a macro scale and/or a micro scale.

[0122] As visible from the figures, the shape of the structured surface on a macro scale is defined by recesses 13 and protrusions 12. The recesses 13 and protrusions 12 preferably form an undulating or wave-like structure. More specifically, in a proximal-distal cross-section of the anchoring section 10, 30 (perpendicular to the first joint axis Al or ulnar-radial direction as shown in FIG. 2), at least one of the major surfaces has a wave-like or undulating profile.

[0123] This undulating profile of the anchoring section 10, 30 particularly extends laterally, i.e. in the direction of the anchoring section's width.

[0124] In other words, the recesses 13 and protrusions 12 extend in the width direction of the anchoring section 10, 30, i.e. the width direction (lateral direction) of the implant.

[0125] The recesses 13 provide guidance when laterally implanting the anchoring section 10, 30 of the (assembled) joint implant into a substantially equidistant slit that has been prepared in a phalangeal bone.

[0126] Accordingly, the anchoring sections 10, 30 of the joint sections are preferably configured to be implanted into a slit. The side surfaces of such a slit are substantially at a fixed distance (i.e. slit width).

[0127] The depth of the slit extends in a lateral direction of the phalangeal bone (Z-direction or radial-ulnar direction in FIG. 2) and corresponds to the direction of insertion and lateral direction of the joint implant.

[0128] The slit within the bone tissue is at least opening towards one of the lateral sides and the face side of the phalangeal bone, where the native interphalangeal joint has been resected.

[0129] Preferably, at least three and preferably all of the protrusions 12 define a plane, i.e. their ends in a direction perpendicular to the plate-shaped anchoring sections 10, 30 are arranged in one plane. The same preferably also applies to the recesses 13. Nonetheless, other shapes are also possible such as regular or irregular arranged protrusions that define one or multiple planes.

[0130] As a result, the protrusions 12 all have substantially the same amount of contact with the side surface of a slit that has been prepared in the bone tissue of a phalangeal bone for anchoring the joint implant.

[0131] More specifically, the anchoring sections 10, 30 are pressed laterally into slits that have been prepared in the ends of two adjacent phalangeal bones that face each other. Since ends or tips of the protrusions 12 are arranged on a plane, they will exert approximately the same pressure onto the adjacent bone tissue of a slit's side wall.

[0132] The height between a recess 13 and a protrusion 12 is preferably chosen so that the opposing bone tissue of a slit's side surface is primarily elastically deformed. In other words, the height is chosen so that the deformation of the slit's side surface upon entrance of the protrusion 12 is at least primarily elastic. As a result, the press-fit between the joint implant and the bone tissue is enhanced since a reduction in contact pressure due to damage to the bone tissue is avoided.

[0133] Further and for guidance during insertion of the joint implant as well as for avoiding damage to the bone tissue, the lateral ends of the protrusions 12 and/or recesses 13 in relation to the anchoring sections 10, 30 are preferably provided with chamfers 14.

[0134] The chamfers are at least provided to the lateral side of the anchoring section 10, 30 that faces the phalangeal bone prior and during insertion of the implant. During insertion of the anchoring section 10, 30 the chamfer acts like a wedge gradually bringing the protrusions 12 of the anchoring section 10, 30 into engagement.

[0135] This facilitates an insertion of the implant and makes the process of insertion more stable. In particular, the chamfer helps to prevent the anchoring section from tilting away when pressure is laterally applied to the plate-shaped anchoring section 10, 30 for pressing the anchoring section 10, 30 into the slit of a phalangeal bone.

[0136] The undulating profile of the macro structure also has the advantage to prevent the implant from slipping out of the bone tissue in a proximal-distal direction of the phalangeal bone.

[0137] More specifically, the protrusions pressing into the bone tissue and having an extension in the lateral direction of the anchoring section 10, 30 prevent the anchoring section 10, 30 from being pulled out of the bone. In this respect, it is preferred that both major surfaces of an anchoring section 10, 30 have an undulating profile in a lateral cross-section. Such a configuration renders an anchoring section more elastic, which can provide a press-fit that adapts to differences in bone density along the slit.

[0138] Even more preferably, the undulating profiles of the opposite major surfaces of the plate-shaped anchoring section 10, 30 are basically extending along the anchoring section 10, 30 in a proximal-distal direction in parallel so that on the side opposite of a protrusion 12 (i.e. at the same location in the proximal-distal direction of the implant but on the other or opposite major surface) is a recess 13 and vice versa (see FIGS. 1, 3, 5, and 6). This results in the surface of a lateral edge (side edge) of such an anchoring section 10, 30 having an undulating shape.

[0139] The undulating surface structure may be faceted as shown in the figures, i.e. it is formed by planar surfaces that are angled in relation to each other. Alternatively, or additionally, the undulating surface structure may be curved. For example, the protrusions 12 and/or recesses 13 may have rounded maxima and/or minima, respectively. The undulating surface structure may also be curved with planar minima and/or planar maxima. Also, the undulating surface structure may have a continuously curved profile.

[0140] The undulating surface structure may be regular or irregular, i.e. the protrusions 12 and recesses 13 are formed in the proximal-distal direction of the implant at regular or irregular distances from each other.

[0141] This is advantageous for different bone densities along an anchoring section. For example, smaller distances may be used for an area with primarily spongious bone tissue and larger distances may be used for an area with primarily cortical bone tissue.

[0142] As described above, the macro structure improves the primary stability of the implant after insertion. In other words, the macro structure helps in preventing a relative movement between the bone tissue of an interphalangeal bone and the surface of an anchoring section 10, 30. This stability in anchoring improves the conditions for a permanent fixation of the joint implant by bone in growth, the so-called secondary stability.

[0143] For enhancing the secondary stability, at least a part of the surface of the anchoring sections 10, 30 preferably includes a microstructure. This microstructure fosters bone ingrowth by providing a surface that supports the creation of bone tissue by osteoblasts. As already described above, such a surface is preferably provided using a plasma spray coating, in particular a titanium plasma spray coating. Nonetheless, other techniques such as 3D printing may be used to create a surface structure for enhancing bone ingrowth. These surface structures are preferably porous surface structures.

[0144] Returning to FIG. 1, the bone shield 60 of the second component 2 may comprise a bone shield abutment surface 61 that limits the range of motion in extension. More specifically, the bone shield abutment surface 61 abuts or gets into contact with an abutment surface 28 of the first joint section 20 if the joint implant is in extension.

[0145] Likewise, the bone shield 60 may have an abutment surface 62 that faces into the opposite circumferential direction to the abutment surface 61. This abutment surface 62 faces and abuts an abutment surface 27 of the first joint section 20 when the joint implant is positioned in maximum flexion (see FIGS. 3 and 6).

[0146] The outer surface 22 of the first joint section 20 is preferably substantially flush with the outer surface 64 of the bone shield 60. This is particularly illustrated in FIG. 1, in which the joint implant is in maximum extension and the abutment surface 61 of the bone shield 60 is in contact with the abutment surface 28 of the first joint section 20.

[0147] Turning to FIG. 4, this figure shows a detailed view of the second joint section 40 being installed within the recess of the first joint section 20 so that the first joint axis Al of the first joint section 20 is aligned with the second joint axis A2 of the second joint section 40. These axes A1, A2 are aligned if the convex joint surface 41 of the second joint section 40 is in contact with the concave joint surface 21 of the first joint section 20.

[0148] As shown in FIG. 4, a recess of the first joint section 20 for accommodating the second joint section 40 is formed by the concave joint surface 21 and two support faces 23 located at the ends of the concave joint surface 21 in the lateral direction of the joint implant. The concave joint surface 21 has a circular profile in a cross-section perpendicular to the second joint axis A2 forming the female surface of the hinge joint. Preferably, the concave joint surface 21 has at least a constant radius in its central portion that interacts with the convex joint surface 41 of the second joint section 40, i.e. the part of the circumferential surface of the second joint section 40 that forms the male surface of the hinge joint. Even more preferably, the concave joint surface has a circular cylindrical shape.

[0149] As illustrated in FIGS. 4 and 6, a retaining pin 24 may protrude from each of the support faces 23 into aforenoted recess formed by the concave joint surface 21 and the support faces 23.

[0150] Consequently, these retaining pins 24 are located on opposite sides and face each other. Preferably, the retaining pins 24 are cylindrical and in particular circular cylindrical. They preferably protrude perpendicular to the support faces 23 along and aligned with the first joint axis A1 of the first component 1.

[0151] Turning to the second joint section 40, the joint section 40 is generally formed as a solid of revolution. Nonetheless, as will be explained below in more detail in relation to the compensation mechanism 50, the second joint section 40 preferably has a flat joint section abutment surface 53 and a hole 52.

[0152] This flat joint section abutment surface 53 forms part of the circumferential surface 42 of the second joint section 40. The hole 52 for receiving a pin 51 of the compensation mechanism 50 has an opening in the joint section abutment surface 53 (see FIG. 4) and preferably an opening on the opposite side facing the concave joint surface 21 of the first joint section 20.

[0153] At each of the two ends along the second joint axis A2, the second joint section 40 comprises an end face 43 and a retaining groove 44. The second joint axis A2 defines the central axis of the convex joint surface 41 and is the axis of symmetry of the solid of revolution generally forming the second joint section 40.

[0154] As illustrated in the figures, the second joint section 40 is preferably barrel-shaped. In other words, the circumferential surface 42 of the second joint section 40 comprises a central portion along the second joint axis A2 having a circular outer cross-section (except for the joint section abutment surface that is preferably flat). This circular cross-section defines a cylindrical section 46, which forms the convex joint surface 41.

[0155] At least on one side but preferably on both sides of this cylindrical section 46 are tapered sections 55. The transition between the circular cylindrical section 46 and the tapered section(s) 55 is preferably rounded, i.e. continuous, in order to prevent stress concentrations that may otherwise occur at an edge formed between the cylindrical section 46 and a tapered section 55.

[0156] For the same reason, the transition between the tapered sections 55 and the end faces 43 of the second joint section 40 is formed by a rounded section 56 having a rounded surface that connects a tapered section 55 and an end face 43. Here too, the transition between the tapered sections and the rounded surface is preferably continuous to avoid stress concentrations upon loading of the joint.

[0157] As a result of this configuration of the second joint section 40, the concave joint surface 21 may only be contact with the corresponding convex joint surface 41 in a central portion of the joint along the joint axes A1, A2.

[0158] Further, due to the reduced diameters of the tapered sections 55 and the rounded transition sections 56, a gap is formed between the preferably cylindrical concave joint surface 21 of the first joint section 20 and the circumferential surface 42 of the second joint section 40. This gap provides space for joint liquid and, thus, helps in stabilizing a fluid film between the concave joint surface 21 and the convex joint surface 41 in an implanted state of the joint implant. This fluid film reduces the friction in the hinge joint of the implant and, thus, enhances its service life.

[0159] As previously described, the retaining pins 24 of the first joint section 20 and the retaining grooves 44 of the second joint section 40 interact with each other. During assembly, the second joint section 40 is moved into the recess formed by the concave joint surface 21 with the portion of the circumferential surface 42 that after assembly functions as convex joint surface 41 facing into the same direction as the concave joint surface 21 (see FIG. 6). In other words, the second joint section is offset about the second joint axis A2 by approximately 180° during assembly in relation to its orientation in extension of the joint implant after assembly.

[0160] This results in the end of the retaining grooves 44 at the circumferential surface 42 facing the retaining pins 24 so that the retaining pins 24 of the first joint section 20 can enter and engage the retaining grooves 44 of the second joint section 40. As shown in the figures, the other end of the retaining grooves 44 is preferably located approximately in the center of the end face 43 so that the retaining pins 24 are positioned in the retaining grooves 44 in the assembled state of the joint, while the joint axes A1 and A2 are aligned (and the concave joint surface 21 is in contact with the convex joint for surface 41).

[0161] As described above, the joint implant may further comprise a compensation mechanism 50 that preferably acts between the second joint section 40 and the bone shield 60 including the second anchoring section 30. The compensation mechanism 50 is configured to compensate forces acting in a proximal-distal direction of the joint implant and/or torque that acts about the longitudinal axis of the joint implant.

[0162] The compensation mechanism 50 comprises a translational and/or rotational joint that keeps forces and/or torque acting between the second anchoring section 30 and the second joint section 40 from being transferred.

[0163] It is assumed that the loads and the torque that is compensated for by a movement of this compensatory joint of the compensation mechanism 50 at least partly exist due to differences between the artificial hinge joint and a native interphalangeal joint. These differences may also be caused upon implantation of the joint implant, for example by an alignment of the implant between the two opposing phalangeal bones that, for example, results in the rotational axis of the joint implant being different from the joint axis of the native interphalangeal joint that has been resected. Further, the muscles and tendons surrounding the interphalangeal joint implant may cause differences due to their location after implantation. Here, the compensation mechanism 50 at least helps in overcoming these differences so that an adverse effect thereof onto the longevity of the interphalangeal joint implant can be avoided.

[0164] The compensation mechanism 50 is configured to adjust or change the relative position and/or orientation between the second joint section 40 and the bone shield 60 with the second anchoring section 30 instead of transferring forces and/or torque acting along and about the longitudinal axis, respectively. Thus, loads that previously have been transferred via the joint surfaces of the hinge joint are reduced, which has a positive effect on the lifespan of the joint implant.

[0165] The exemplary interphalangeal joint implant according to the present disclosure shown in the figures is configured for compensating both between the second joint section 40 and the second anchoring section 30, i.e. longitudinal forces acting along the fourth joint axis A4 as well as rotational forces (i.e. torque) acting about the fourth joint axis A4.

[0166] This is achieved by the compensation mechanism 50 being configured as a joint with these 2 degrees of freedom. As particularly illustrated in FIG. 5, this joint comprises a pin 51 that protrudes along and is preferably aligned with the fourth joint axis A4. The pin protrudes from the inner surface 63 of the bone shield 60 and is preferably integrally formed. This figure further illustrates that the pin comprises a base portion having a larger diameter than the pin 51 so that a step is formed between this base portion and the pin 51.

[0167] This step includes an annular surface that faces the second joint section 40 and in particular the preferably flat joint section abutment surface 53 and acts as an anchoring section abutment surface 54, as will be explained in more detail further below.

[0168] In order to allow for a rotational and translational movement, the pin 51 preferably has a cylindrical shape with a circular cross-section. Preferably, the pin 51 and its base portion is integrally formed with the bone shield 60 and/or the anchoring section 30.

[0169] As already noted above, the second joint section 40 includes a hole 52 functionally belonging to the compensation mechanism 50 that corresponds to the pin 51 protruding from the bone shield 60 in order to function as a translational and rotational joint. As described above, the hole 52 of the compensation mechanism 50 is preferably formed as a through hole in order to allow for a smooth translational movability of the pin 51 into and out of the hole 52. More specifically, in the environment of the hole 52 and the pin 51 will be joint liquid in an implanted state. By configuring the hole 52 as a through hole, any liquid present in front of the face side of the pin 51 will be able to escape through the end of the through hole 52 that faces the concave joint surface 21 of the first joint section 20.

[0170] Nonetheless, the hole 52 may also be configured as a blind hole in order to achieve a dampening effect for the relative movement between the second anchoring section 30 and the second joint section 40 in the translational direction along the fourth joint axis A4.

[0171] If a compensation mechanism 50 is present, aforenoted gap between the inner surface 63 of the bone shield 60 and the circumferential surface 42 of the second joint section 40 may not only assist in lubricating the hinge joints but may further serve for the compensation mechanism 50 being able to perform a relative rotation about the fourth joint axis A4 if the pin 51 is at an end position within the hole 52.

[0172] In this end position, the anchoring section abutment surface 54 of the pin 51 is in contact with the joint section abutment surface 53 of the second joint section 40. In extension of the joint implant, the joint section abutment surface 53 is arranged to substantially face into the same direction as the concave joint surface 21 of the first joint section 20 in the assembled state of the implant (cf. FIG. 5).

[0173] In order for the compensation mechanism 50 to be able to rotate in this end position, there is particularly a wedge like gap between the tapered sections 55 and the inner surface 63 of the bone shield 60.

[0174] In other words, at both ends of the joint section 40 and the bone shield 60 (at least at one of their ends) the gap between the inner surface 63 and the tapered section 55 increases in width.

[0175] Further, for a smooth rotation about the fourth joint axis A4, there is preferably also a gap present in the central portion along the third joint axis A3 that faces the cylindrical section 46 the second joint section 40.

[0176] Alternatively, the outer surface 42 of the second joint section 40 may be curved at the cylindrical section 46 in a cross section along the second joint axis A2 to allow for such a smooth rotation.

[0177] Further, the inner surface 63 of the bone shield 60 may also be curved. For example, the inner surface 63 has a radius that is larger than a radius of the outer surface 42. The outer circumferential surface 42 of the joint section 40 preferably has a higher curvature than the inner surface 63 of the bone shield 60, in particular for allowing for above-noted smooth rotation about the fourth joint axis A4.

[0178] Due to the presence of this gap, the second anchoring section 30 is able to rotate about the fourth joint axis A4 and relative to the second joint section 40 in afore-noted end position with an abutment of the joint section abutment surface and the anchoring section abutment surface. This relative rotation has a range of motion in aforenoted ranges that is limited due to the inner surface 63 of the bone shield 60 getting into contact with the inclined surfaces of the tapered sections 55 (depending on the configuration of the tapered section, these inclined surfaces may be linear or curved). This contact is preferably configured as a line contact or a surface contact of the inner surface 63 with the surface of the tapered sections 55 in order to avoid stress concentrations during an abutment of these surface.

[0179] If such a compensation mechanism 50 is included in an interphalangeal joint according to the present disclosure, the kinematic behavior of the joint is closer to the kinematic behavior of a native interphalangeal joint since it does not only allow a rotation about the hinge joint axis A1, A2 but also a rotation about the fourth joint axis A4 in aforenoted ranges.

[0180] This is achieved in a defined movement of the individual joints that prevents the feeling of a wobbly joint. Instead, the interphalangeal joint implant provides the stable impression of a native joint. In other words, an interphalangeal joint implant with such a compensation mechanism mimics the anatomic rotational-sliding movement of a native joint.

REFERENCE SIGNS

[0181] The following lists the reference signs used in the description and the drawings. Throughout the drawings these reference signs refer to features that have the same or an equivalent function and/or structure.

[0182] 1 first component

[0183] 2 second component

[0184] 10 first anchoring section

[0185] 11 surface structure

[0186] 12 protrusion of surface structure

[0187] 13 recess of surface structure

[0188] 14 chamfer of surface structure

[0189] 20 first joint section

[0190] 21 concave joint surface

[0191] 22 outer surface of the first joint section

[0192] 23 support face

[0193] 24 retaining pin

[0194] 27 abutment surface in flexion

[0195] 28 abutment surface in extension

[0196] 30 second anchoring section

[0197] 40 second joint section

[0198] 41 convex joint surface

[0199] 42 circumferential surface

[0200] 43 end face

[0201] 44 retaining groove

[0202] 46 cylindrical section of/forming convex joint surface

[0203] 50 compensation mechanism

[0204] 51 pin of compensation mechanism

[0205] 52 hole of compensation mechanism

[0206] 53 joint section abutment surface

[0207] 54 anchoring section abutment surface

[0208] 55 tapered section

[0209] 60 bone shield

[0210] 61 bone shield abutment surface in extension

[0211] 62 bone shield abutment surface in flexion

[0212] 63 inner surface of the bone shield

[0213] 64 outer surface of the bone shield

[0214] A1 first joint axis

[0215] A2 second joint axis

[0216] A3 central axis of bone shield

[0217] A4 translational axis of longitudinal compensation mechanism