ARTIFICIAL JOINT

Abstract

An artificial joint is characterized by: having a first member including a caput part on which a prescribed curved surface is formed, and a second member including a fossa part having a surface which abuts the prescribed curved surface of the caput part; the second member being rotatable in a flexing direction of a joint with a prescribed point on the caput part being the center of rotation; and the prescribed curved surface of the caput part being defined by a curve which depicts a convex arc toward the side abutting the fossa part when the caput part is viewed from the axial direction of the rotation, and in which, when two arbitrary points are taken on the curve, the radius of curvature of the point positioned further toward the flexing side of the joint on the curve is smaller than the radius of curvature of the other point.

Claims

1. An artificial joint used by being implanted in a human body, comprising: a first member including a bone head portion on which a predetermined curved surface is formed and a first stem portion implanted in a first bone; and a second member including a bone fossa portion having a surface in contact with the predetermined curved surface of the bone head portion and a second stem portion implanted in a second bone adjacent to the first bone, wherein the second member is configured to pivot in a bending and stretching direction of a joint about a predetermined point on the bone head portion as a rotation center, and the predetermined curved surface of the bone head portion is defined by a curve that draws a convex arc toward a side abutting on the bone fossa portion when the bone head portion is viewed from an axial direction of the pivoting movement and has, when two arbitrary points are taken on the curve, a curvature radius at a point located closer to a bending side of the joint on the curve which is smaller than a curvature radius at another point.

2. The artificial joint according to claim 1, wherein the curve is a curve constituting a part of a locus of a logarithmic spiral.

3. The artificial joint according to claim 2, twherein the curve is a curve constituting a part of a locus of a logarithmic spiral defined by a Fibonacci sequence.

4. The artificial joint according to claim 1, wherein the bone fossa portion has a side surface that forms a slope extending outward in the axial direction of the pivoting movement from a stretching side to a bending side of the joint.

5. The artificial joint according to claim 4, wherein the bone fossa portion has a substantially trapezoidal contour whose width on the bending side is larger than a width on the stretching side of the joint when the bone fossa portion is viewed from a surface side abutting on a predetermined curved surface of the bone head portion.

6. An artificial joint used by being implanted in a human body, comprising: a first member including a bone head portion on which a predetermined curved surface is formed and a first stem portion implanted in a first bone; and a second member including a bone fossa portion having a surface in contact with the predetermined curved surface of the bone head portion and a second stem portion implanted in a second bone adjacent to the first bone, wherein the second member is configured to pivot in a bending and stretching direction of the joint about a predetermined point on the bone head portion as a rotation center, and the bone fossa portion has a side surface that forms a slope extending outward in an axial direction of the pivoting movement from a stretching side to a bending side of the joint.

7. The artificial joint according to claim 6, twherein the bone fossa portion has a substantially trapezoidal contour whose width of a lower portion is larger than a width of an upper portion when the bone fossa portion is viewed from the front.

8. The artificial joint according to claim 1, wherein the bone head portion includes two convex condylar portions arranged in an axial direction of the pivoting movement and a valley portion positioned between the two condylar portions, and the bone fossa portion includes a central convex portion engaged with the valley portion and concave condylar receiving portions located on both sides of the central convex portion and engaged with the condylar portion, and a predetermined curved surface of the bone head portion is formed at the condylar portion.

9. The artificial joint according to claim 8, wherein the valley portion has a structure in which a stretching side of the joint is shallow and gradually deepens toward a bending side of the joint, and the central convex portion has a structure in which a height gradually changes so that the stretching side and the bending side of the joint are high and a middle between the stretching side and the bending side is lowest.

10. The artificial joint according to claim 1, wherein the bone fossa portion is formed of a metal.

11. The artificial joint according to claim 1, wherein the artificial joint is applied to a knee joint of a human body.

12. The artificial joint according to claim 1, wherein the artificial joint is applied to an elbow joint of a human body.

13. The artificial joint according to claim 1, wherein the artificial joint is applied to a finger joint of a human body.

14. The artificial joint according to claim 13, wherein the artificial joint is applied to a proximal interphalangeal joint or a metacarpophalangeal joint.

15. The artificial joint according to claim 6, wherein the bone head portion includes two convex condylar portions arranged in an axial direction of the pivoting movement and a valley portion positioned between the two condylar portions, and the bone fossa portion includes a central convex portion engaged with the valley portion and concave condylar receiving portions located on both sides of the central convex portion and engaged with the condylar portion, and a predetermined curved surface of the bone head portion is formed at the condylar portion.

16. The artificial joint according to claim 15, wherein the valley portion has a structure in which a stretching side of the joint is shallow and gradually deepens toward a bending side of the joint, and the central convex portion has a structure in which a height gradually changes so that the stretching side and the bending side of the joint are high and a middle between the stretching side and the bending side is lowest.

17. The artificial joint according to claim 6, wherein the bone fossa portion is formed of a metal.

18. The artificial joint according to claim 6, wherein the artificial joint is applied to a knee joint of a human body.

19. The artificial joint according to claim 6, wherein the artificial joint is applied to an elbow joint of a human body.

20. The artificial joint according to claim 6, wherein the artificial joint is applied to a finger joint of a human body.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0031] FIG. 1A is a side view schematically illustrating an artificial joint according to an embodiment. FIG. 1B is a plan view schematically illustrating an artificial joint according to an embodiment.

[0032] FIG. 2 is a view for explaining the shape of a condylar portion of the artificial joint according to the embodiment.

[0033] FIG. 3A is the first view for explaining the pivoting movement of the artificial joint according to the embodiment. FIG. 3B is the second view for explaining the pivoting movement of the artificial joint according to the embodiment. FIG. 3C is the third view for explaining the pivoting movement of the artificial joint according to the embodiment.

[0034] FIG. 4 is a front view illustrating the bone fossa portion of the artificial joint according to the embodiment.

[0035] FIG. 5A is the first view illustrating the positional relationship between the bone fossa portion and the lateral cord accompanying the bending and stretching motion of a finger to which the artificial joint according to the embodiment is applied. FIG. 5B is the second view illustrating the positional relationship between the bone fossa portion and the lateral cord accompanying the bending and stretching motion of the finger to which the artificial joint according to the embodiment is applied.

DESCRIPTION OF EMBODIMENTS

[0036] The present invention will be exemplarily described below based on embodiments with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in the embodiments are not intended to limit the scope of the present invention only to them unless otherwise specified. In the following description, the same reference numerals are used for the same elements, and redundant description will be omitted.

First Embodiment

[0037] FIG. 1 schematically illustrates an artificial joint 1 according to the present embodiment. FIG. 1A is a side view of the artificial joint 1. FIG. 1B is a plan view of the artificial joint 1. The artificial joint 1 according to the present embodiment is an artificial joint that substitutes for a proximal interphalangeal joint (so-called second joint) of a finger and, as illustrated in FIG. 1, includes a set of a proximal side member 10 arranged on a proximal phalanx side and a distal side member 20 arranged on a middle phalanx side.

[0038] The proximal side member 10 includes a bone head portion 11 that substitutes for a distal end portion of a proximal phalanx, and a proximal side stem portion 12 embedded in the proximal phalanx. The bone head portion 11 is preferably formed of, for example, a resin having excellent abrasion resistance such as ultrahigh molecular weight polyethylene. The effect of wear can be reduced when the bone head portion is combined with a distal side member having a metallic bone fossa portion.

[0039] In addition, the bone head portion 11 is configured to include two condylar portions 111a and 111b that are convex toward the distal side and a valley portion 112 positioned between them. The condylar portions 111a and 111b have curved surfaces defined by curves as described later, and the valley portion 112 has a structure in which the upper side is shallow and gradually deepens toward the lower side.

[0040] The distal side member 20 includes a bone fossa portion 21 that substitutes for a proximal end portion of the middle phalanx and a distal side stem portion 22 implanted in the middle phalanx. The bone fossa portion 21 is formed of, for example, a metal such as a cobalt-chromium alloy or pure titanium and can maintain strength even when the thickness is reduced.

[0041] Since the thickness of the bone fossa portion 21 can be formed thin, it is possible to preserve and restore more ligamentous attachment portions of the bone at the time of joint replacement surgery. This makes it possible to preserve more ligaments (and tendons) without removing them. This can accelerate the recovery of the joint function.

[0042] In addition, the bone fossa portion 21 includes a central convex portion 211 that engages with the valley portion 112 and concave condylar receiving portions 212a and 212b that are located on both sides of the central convex portion and respectively engage with the condylar portions 111a and 111b. The central convex portion 211 has a structure in which the height gradually changes so that the upper side and the lower side are high and the middle is the lowest.

[0043] The proximal side stem portion 12 and the distal side stem portion 22 may be configured to be implanted in the bone by a desired known technique and are formed of metal in the present embodiment.

[0044] The condylar portions 111a and 111b of the bone head portion 11 each have a convex curved surface on the distal side, and the curved surface has a shape that is a so-called Fibonacci curve when the bone head portion 11 is viewed from the side surface as illustrated in FIGS. 1A and 2. The Fibonacci curve is a curve constituting a part of the locus of a logarithmic spiral (also referred to as a golden spiral) derived from the Fibonacci sequence. FIG. 2 is a view illustrating a golden spiral in a side view of the bone head portion 11 such that a part of the locus of the spiral overlaps a convex curve of the condylar portion 111a.

[0045] The distal side member 20 is vertically pivotal about a predetermined point on the bone head portion 11 of the proximal side member 10 as a rotation center and reproduces the bending and stretching motion of the finger by the pivoting movement. FIG. 3 illustrates a state in which the distal side member 20 rotates about the rotation center of the bone head portion 11. FIG. 3A is a view illustrating a case in which the joint is in a stretched state (rotation angle is 0°). FIG. 3B is a view illustrating a case in which the rotation angle is 45°. FIG. 3C is a view illustrating a case in which the joint is in a bent state. The spiral in FIG. 3 indicates the above golden spiral.

[0046] The curved surfaces of the condylar portions 111a and 111b which abut on the distal side member 20 each are defined by a Fibonacci curve whose distance with respect to the rotation center of the bone head portion 11 decreases (that is, the radius of curvature decreases) toward the bending direction when the bone head portion 11 is viewed from a side surface (that is, the axial direction of the pivoting movement). Therefore, unlike the case of a curved surface defined by a curve that is an arc (that is, a part of the circle), the distal side member 20 can pivot more (for example, at a rotation angle of 100° or more) in the bending direction.

[0047] On the other hand, since the pivoting movement of the distal side member 20 is performed while the bone head portion 11 and the bone fossa portion 21 are in contact with each other, the distal side member 20 is prevented from pivoting upward from the horizontal direction by the configuration of the valley portion 112 and the central convex portion 211 as described above. More specifically, as the distal side member 20 pivots from the lower side to the upper side (the joint changes from the bent state to the stretched state), the valley portion 112 is restrained more greatly with respect to the central convex portion 211, and the restraint is maximized when the joint is in the substantially stretched state. This prevents the distal side member 20 from pivoting further upward.

[0048] In addition, the condylar receiving portions 212a and 212b of the bone fossa portion 21 are formed to engage with the condylar portions 111a and 111b without any gap at the position where the joint is in the stretched state and are formed such that a gap is slightly generated in the left-right direction at the position where the joint is in the bent state. Accordingly, the degree of freedom in the left-right direction can be obtained in a state where the joint is bent as in the case of a healthy joint.

[0049] FIG. 4 is a view illustrating a state in which the bone fossa portion 21 of the artificial joint 1 after being replaced as a joint in the human body is viewed from the front (that is, the surface on the side abutting on the bone head portion 11). The broken line in FIG. 4 indicates a trapezoid having an upper side shorter than a lower side. As illustrated in FIG. 4, when viewed from the front, the bone fossa portion 21 has a structure in which the width on the upper side is shorter than the width on the lower side, and both side surfaces have inclined surfaces expanding outward from the upper side to the lower side. That is, the bone fossa portion 21 has a substantially trapezoidal contour as indicated by the broken line in FIG. 4. Although not illustrated, the bone head portion 11 abutting on the bone fossa portion 21 also has a substantially trapezoidal shape when viewed from the front (that is, the surface on the side abutting on the bone fossa portion 21).

[0050] In a finger of the healthy living body, a lateral cord exists over the distal side and the proximal side of the joint and also functions as a tendon for bending the joint. FIG. 5 is a view illustrating the positional relationship between the bone fossa portion 21 and the lateral cord 51 accompanying the bending and stretching motion of the finger to which the artificial joint 1 is applied. FIG. 5A is a view illustrating the positional relationship between the bone fossa portion 21 and the lateral cord 51 in a state where the joint is stretched. FIG. 5B is a view illustrating the positional relationship between the bone fossa portion 21 and the lateral cord 51 in a state where the joint is bent. As illustrated in FIG. 5, the lateral cord 51 slides on the side surface from the upper surface of the joint in accordance with the bending and stretching motion of the finger, is arranged together on the upper side of the joint when the joint is stretched, and is divided into two and arranged on both side surfaces of the joint when the joint is bent.

[0051] Since the shapes of the bone fossa portion 21 and the bone head portion 11 are configured to have inclined surfaces extending outward from the upper side to the lower side on both side surfaces as described above, the sliding motion of the lateral cord from the upper surface to the side surface of the joint as described above is not hindered and smoothly performed, and thus the bending and stretching motion of the finger can be smoothly performed.

<Others>

[0052] Note that the description of the above embodiment is merely illustrative of the present invention, and the present invention is not limited to the above specific embodiment. The present invention allows various modifications and combinations of techniques within the scope of the technical idea. For example, the present invention can be applied not only to the proximal interphalangeal joint but also to an artificial joint of a finger such as a metacarpophalangeal joint. In addition, the present invention can be applied not only to the joint of the finger but also to an artificial joint of another joint of the four limbs of the human body such as an elbow joint and a knee joint.

[0053] The curves of the condylar portions 111a and 111b do not necessarily form a part of the locus of a golden spiral and may be any curves as long as the distance from the rotation center gradually decreases toward the bending side. In addition, the shapes of the bone fossa portion and the bone head portion when viewed from the front each are not necessarily trapezoidal and may be a substantially triangular shape.

REFERENCE SIGNS LIST

[0054] 1 artificial joint

[0055] 10 proximal side member

[0056] 11 bone head portion

[0057] 111 condylar portion

[0058] 112 valley portion

[0059] 12 proximal side stem portion

[0060] 20 distal side member

[0061] 21 bone fossa portion

[0062] 211 central convex portion

[0063] 212 condylar receiving portion

[0064] 22 distal side stem portion

[0065] 51 lateral cord