Artificial finger joint and distal side member thereof

Abstract

Provided are: an artificial finger joint that can be stably fixed by a simple method of mere insertion, and that can reduce the risk of loosening after implantation thereof; and a distal side member of the artificial finger joint. This artificial finger joint comprises: a bone axis pin 6 that can be inserted into a medullary cavity 21 such that the bone axis pin 6 extends from a joint receiving part 5 along a bone axis 11 and penetrates through a cortical bone 22; and at least two palmar side pins 7 that each extend from the joint receiving part and can be inserted into the cortical bone, the palmar side pins 7 being shorter than the bone axis pin and located further toward the palmar side than the bone axis pin. Each of the centers of the at least two palmar side pins is located in a palmar side half area and the center of the bone axis pin is located in a dorsal side half area, the palmar side half area and the dorsal side half area being two equal areas obtained by dividing the joint receiving part in the palmar-dorsal direction.

Description

Artificial finger joint and its distal component

[0001] The present invention relates to an artificial finger joint portion that is fixed to the bones of the fingers or toes and its distal member.

[0002] Conventionally, artificial finger joints of this type have been known to have various structures.

[0003] For example, as shown in Figures 6A to 6D, the implant of the artificial joint is composed of a proximal member 103 on the spherical convex side having an approximately hemispherical head 101 and a stem 102 extending from the flat surface of the head 101, and a distal member (not shown) on the approximately hemispherical concave side with which the head 101 can be flexibly engaged.

[0004] In such an implant, first, a large portion 201 of the cortical bone of the finger that faces the glenoid cavity is removed, as shown in FIGS. 6A and 6B.

[0005] Next, as shown in Figure 6C, the stem 102 is inserted from the resected surface through the cancellous bone 224 into the soft medullary cavity 203 which is located within the hard cortical bone 202 and is free of bone, and is fixed by adhering it to the cortical bone of the diaphysis from the inside.

[0006] In this way, implants of the type that fix the stem 102 by closely contacting it from the inside to the cortical bone of the diaphysis have had problems such as unstable fixation of the implant and difficulty in optimizing the stem size due to variations in the medullary cavity 203 between individuals, which causes the size of the medullary cavity 203 and the stem 102 to not match. Also, as shown in Figure 6D, because the stem 102 is inserted only into the medullary cavity 203, the medullary cavity 203 is too soft and is prone to sinking into the bone.

[0007] In contrast, some implants use bone cement to fill the gap between the medullary cavity and the stem, but this procedure is complicated and costly.

[0008] One method for solving these problems is the artificial joint fixing structure disclosed in Patent Documents 1 and 2.

[0009] 7A and 7B, the fixing structure of this artificial joint has a tapered slit 207 formed from the base of a substantially rod-shaped stem 204 toward the tip, and a screw hole 208 formed in the base to communicate with the slit 207, and a set screw 209 of a required length is threadably incorporated into the screw hole 208 to expand the tip of the stem 204 outward. By screwing the set screw 209 and press-fitting it into the slit 207, the tip of the stem 204 expands outward and is fixed by pressure contact with the inner surface 217 of the cortical bone of the diaphysis.

[0010] Patent No. 3614802 Publication Patent No. 2964035 Publication Special Publication No. 2022-502203

[0011] However, with the fixation structure, the stem 204 must be inserted into the bone and then the set screw 209 must be turned, which is a complicated procedure. In addition, it is said that the expanding stem 204 is thin and prone to breakage, and that the load is concentrated in a local area of ​​the bone, causing bone resorption or fracture.

[0012] Furthermore, Patent Document 3 discloses a method for minimizing the amount of cortical bone removed and preserving bone by inserting multiple supports 221, 222 into cancellous bone and cortical bone, as shown in Fig. 8. Although it is intended for metatarsals, it is also described as being applicable to finger joints.

[0013] However, with this structure, although the fixation pin is inserted into the hard bone part of the joint surface, there is a risk of loosening after implantation, and because the pin is positioned independently of the bone axis, it may be misaligned with the center of gravity, resulting in stability problems.

[0014] Therefore, the object of the present invention is to solve the above problems by providing an artificial finger joint and its distal component that can be stably fixed by the simple method of simply inserting it and that reduces the risk of loosening after implantation.

[0015] In order to achieve the above object, the present invention is configured as follows.

[0016] According to one aspect of the present invention, there is provided a distal component of an artificial finger joint comprising: a joint receiving part that is disposed on the articular surface of the bone and has a spherical concave part that engages with the spherical convex part of the proximal component to allow it to bend freely; a bone axis pin that extends from the joint receiving part along the bone axis, penetrates the cortical bone, and can be inserted into the medullary cavity; and at least two palmar pins that extend from the joint receiving part, are insertable into the cortical bone, are shorter than the bone axis pin, and are located on the palm side of the bone axis pin; and when the joint receiving part is divided into a palmar half region and a dorsal half region in the palm-dorsal direction, the centers of the at least two palmar pins are located in the palmar half region, and the center of the bone axis pin is located in the dorsal half region.

[0017] According to the above aspect of the present invention, stable fixation can be achieved by the simple method of simply inserting the implant into the bone, and the risk of loosening after implantation can be reduced.

[0018] That is, instead of inserting a stem into the medullary cavity and then adhering it to the cortical bone of the diaphysis from the inside, the amount of bone resection at the joint can be minimized, and the bone axis pin and palmar pin can be inserted into the cortical bone of the articular surface for fixation. This eliminates the possibility of unstable fixation of the distal component due to mismatches between the sizes of the medullary cavity, bone axis pin, and palmar pin caused by variations in the medullary cavity between individuals, and allows the sizes of the bone axis pin and palmar pin to be optimized. In particular, since finger joints move more frequently in the flexion-extension direction than the lateral direction, by positioning the center of the palmar pin in the palmar half region of the joint receiving portion and the center of the bone axis pin in the dorsal half region, the fixation component can be positioned on both the palmar and dorsal sides, providing stability against flexion and extension movements of the finger.

[0019] Furthermore, since the bone axis pin is arranged coaxially with the bone axis, it is arranged at the center of gravity, which improves stability during fixation.

[0020] Furthermore, since three or more pins, including the bone shaft pin and the palmar pin, are arranged in a non-linear manner, greater stability can be achieved with respect to finger movements (for example, extension-flexion and radioulnar flexion).

[0021] In this way, stability during fixation can be improved, and greater stability can be achieved with respect to finger movements (e.g., extension-flexion, radial-ulnar flexion), reducing the risk of loosening after implantation.

[0022] FIG. 1 is a side view of an artificial finger joint according to one embodiment of the present invention; FIG. 2 is a side view of a distal member of the artificial finger joint; FIG. 3 is a back view of the distal member; FIG. 4 is a back view of the distal member; FIG. 5 is an explanatory diagram of finger extension and flexion movement; FIG. 6 is an explanatory diagram of radioulnar flexion movement of the MP joint; FIG. 7 is an explanatory diagram of a fixing method for an artificial finger joint; FIG. 8 is an explanatory diagram of a fixing method for an artificial finger joint; FIG. 9 is an explanatory diagram of a conventional fixing method for an artificial finger joint; FIG. 10 is an explanatory diagram of a fixing structure for another conventional artificial joint; FIG. 11 is an explanatory diagram of a fixing structure for yet another conventional artificial joint

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0024] As shown in FIG. 1 , an artificial finger joint 1 according to an embodiment of the present invention includes a proximal member 3 and a distal member 2 .

[0025] Of these, the distal side member 2 includes a joint receiving portion 5, a bone shaft pin 6, and at least two palm side pins 7, as shown in FIGS. 1 to 3B.

[0026] The joint receiving portion 5 is placed on the joint surface of the bone, and has a spherical recess 2a on the surface of a roughly rectangular plate-shaped member that comes into contact with and engages with the spherical protrusion 3a of the proximal member 3, allowing it to slide and bend freely.

[0027] The thickness of the thinnest portion 2c of the spherical recess 2a of the joint support 5 is 1 mm or less and 0.1 mm or more. This has the effect of reducing the amount of cortical bone 22 resected on the glenoid cavity side to secure the joint support 5. Furthermore, the palmar-dorsal dimension of the joint support 5 is smaller than the palmar-dorsal dimension of the cortical bone, and the difference therebetween relative to the cut surface of the bone is preferably 0 mm or more and 2 mm or less. This allows a portion of the joint support 5 to be placed on the cortical bone 22, enabling stable placement. That is, with this configuration, by making the joint support 5 larger in size so as not to exceed the cut surface of the bone and to a degree that does not damage other tissues, the distal side component 2 rests on the cortical bone 22, and the distal side component 2 is supported by the cortical bone 22, resulting in stability.

[0028] The bone axis pin 6 extends from the flat surface 2 b on the rear surface of the joint receiving portion 5 along the bone axis 11 , penetrates the cortical bone 22 , and is arranged so that it can be inserted into the medullary cavity 21 .

[0029] Here, the bone axis 11 in the case of finger bones (for example, the proximal phalanx, the middle phalanx, etc.) means a line that is parallel to the dorsal surface of the bone and passes through approximately the center of the medullary cavity 21. Basically, in a finger, the anatomical bone axis and the mechanical bone axis coincide, and it can be considered that if the pin 6 is located on the bone axis 11, the bone will also be mechanically stable.

[0030] The artificial finger joint part 1 in this embodiment is fixed to the finger so that the bone axis 11 is positioned on the long axis of the pin 9, passing through the most concave part of the spherical recess 2a of the joint receiving part 5 of the distal side member 2, on the long axis of the bone axis pin 6, and passing through the most protruding part of the spherical protrusion 3a of the proximal side member 3.

[0031] The bone axis pin 6 has a truncated cone shape, which makes it easy to insert into the cortical bone 22 or into the cortical bone 22 and the cancellous bone 24 inside the cortical bone 22 on the glenoid side, and also into the medullary cavity 21. The bone axis pin 6 may have a columnar portion (such as a cylindrical or rectangular column) and a conical portion, and it is desirable that the pin be tapered toward the tip.

[0032] Furthermore, the bone axis pin 6 is not inserted only into the medullary cavity 21, but only into the cortical bone 22a on the glenoid cavity side, or inserted into the cortical bone 22a on the glenoid cavity side and then into the cancellous bone 24 close to the glenoid cavity, so that it will not wobble even if the cancellous bone 24 is too soft.

[0033] The length of the bone axis pin 6 needs to be long enough to prevent the pin from coming out when a force is applied to the joint from an unexpected direction. Also, by giving the pin 6 a certain length, the risk of slippage due to a strong moment caused by finger movement is reduced, and the pin 6 can be effectively fixed in place by contacting the cancellous bone 24 near the glenoid cavity.

[0034] More specifically, for example, the bone axis pin 6 penetrates deeply into the articular surface and adheres to the cortical bone 22a of the articular surface and the cancellous bone 24 of the medullary cavity 21, preventing the artificial finger joint 1 from slipping out of the articular surface. Therefore, it is desirable that the length of the bone axis pin 6 be longer than the shortest distance from the center of the bone axis pin 6 to the end of the joint receiving part 5 (e.g., the upper end in FIG. 5C ). Conversely, if the length of the bone axis pin 6 is shorter than the shortest distance from the end of the joint receiving part 5 (e.g., the upper end in FIG. 5C ) to the center of the bone axis pin 6, the distal component 2 may slip if a strong moment is applied. To prevent this, the length of the bone axis pin 6 should be longer than the shortest distance. Furthermore, it is preferable that the length be approximately equal to or greater than the height and width of the articular surface (e.g., 5 mm to 15 mm). Furthermore, it is desirable that the length of the bone axis pin 6 be at least three times the diameter of the bone axis pin 6 at the connection point with the joint receiving part 5.

[0035] The allowable range of deviation between the bone axis 11 and the axis of the bone axis pin 6 is preferably within 0.5 mm as the insertion point of the bone axis pin 6. The reason for this is that any deviation greater than this increases the risk of the artificial finger joint part 1 protruding from the joint surface.

[0036] The at least two palmar pins 7 extend from the flat surface 2b on the rear surface of the joint receiving part 5, for example, along an axis parallel to the bone axis 11, so that they can be inserted into the cortical bone 22a on the glenoid cavity side, are shorter than the bone axis pin 6, and are positioned on the palmar side of the bone axis pin 6. When the joint receiving part 5 is divided into a lower palmar half region 300a and an upper dorsal half region 300b in the palm-dorsal direction (the up-and-down direction in Fig. 3A ) by a bisector 300, the centers of the at least two palmar pins 7 are located in the palmar half region 300a, and the center of the bone axis pin 6 is located in the dorsal half region 300b. With this configuration, particularly because finger joints move more frequently in the flexion-extension direction than the left-right direction, the center of the palmar pin 7 of the joint support 5 is located in the palmar half region 300a and the center of the bone axial pin 6 is located in the dorsal half region 300b. This positions the fixing member on both the palmar and dorsal sides, providing stability against flexion and extension of the finger. Furthermore, when the joint support 5 is bisected by a bisector 310 into a left half region 310a and a right half region 310b in the left-right direction (the left-right direction in FIG. 3B ) perpendicular to the palm-dorsal direction, at least two palmar pins 7 are located in the left half region 310a and the right half region 310b. This configuration also provides stability in the left-right direction. Furthermore, it is desirable for the length of the palmar pin 7 to be less than half the length of the bone axial pin. The palmar pin 7 is inserted and fixed into the cortical bone 22a on the glenoid cavity side, thereby preventing rotation of the artificial finger joint 1. Alternatively, the palmar pin 7 may be inserted through the cortical bone 22a and into the cancellous bone 24, so that the palmar pin 7 and the cancellous bone 24 are bonded together.

[0037] As a material factor to eliminate loosening after implantation, a coating that easily adheres to bone (for example, a pure titanium plasma spray coating) can be applied to the flat surface 2b on the back side of the joint receiving part 5 (the part that comes into contact with the osteotomy surface of the bone) to increase stability.

[0038] Each palmar pin 7 has a cylindrical portion 7b protruding from the flat surface 2b, which can be inserted into the cortical bone 22a on the glenoid cavity side. The cylindrical portion 7b ensures a large contact area with the cortical bone 22a on the glenoid cavity side, making it less likely to come out.

[0039] Each palmar pin 7 has a truncated cone portion 7a at the tip of the cylindrical portion 7b, which has the effect of making it easier to insert the truncated cone portion 7a into the cortical bone 22a on the glenoid cavity side.

[0040] Each palmar pin 7 penetrates into the cortical bone 22a on the glenoid cavity side of the bone joint surface and serves to prevent rotation of the artificial finger joint portion 1. Therefore, it is preferable that the length of each palmar pin 7 be set to a minimum length (e.g., 1.5 mm or more) that allows it to penetrate into the cortical bone 22a on the glenoid cavity side. In other words, if the length of each palmar pin 7 is too long, it will break through the cortical bone 22a other than the cortical bone 22a on the glenoid cavity side, and if it is too short, it will not be able to penetrate the cortical bone 22a on the glenoid cavity side and will not be able to be stably fixed. For this reason, the length of each palmar pin 7 is preferably set within the range of 1.5 mm to 4 mm.

[0041] Although it is preferable that the lengths of the palmar pins 7 are the same, they may be different in length. If the lengths are different, it is possible to set the palmar pins 7 with more appropriate dimensions when there is a difference in the shapes of the left and right phalanges.

[0042] The cross-sectional shape of the palmar pin 7 in the direction perpendicular to the axis is not limited to a circle, but may be a triangle, a square, a semicircle, a D-shape, or a rectangle formed by connecting two palmar pins 7. Furthermore, the palmar pin 7 may be cylindrical or rectangular without the truncated cone 7a. For example, the palmar pin 7 has a cylindrical portion 7b with a diameter of approximately 1.2 to 2.0 mm, a tip of the truncated cone portion 7a with a diameter of approximately 1 mm, and a length of 2 to 4 mm. The bone shaft pin 6 has a maximum diameter of 2 to 4 mm and a length of 7.5 to 13 mm. The joint receiving portion 5 has a vertical width of 6 to 11 mm and a horizontal width of 8 to 14 mm. Because of the small overall dimensions of the artificial finger joint 1, a circular shape offers the advantage of easier processing. That is, a circular shape is preferable for the purpose of drilling a pilot hole in the articular surface of the bone with a K-wire, and for the sake of shape consistency.

[0043] Regarding the arrangement of the pins 6 and 7, the bone axis pin 6 is placed at the vertex 12a, which is the vertex shared by two equal sides of the isosceles triangle 12, on the flat surface 2b on the underside of the joint support 5, and at least two palmar pins 7 are placed at the remaining two vertices 12b. Considering finger movement, if the three pins were aligned in a straight line, the pins would be weak and unable to withstand the load in the palmar-dorsal direction during the finger extension-flexion movement shown in Figure 4A. In contrast, placing the pins 6 and 7 at the three vertices 12a and 12b of the triangle has the effect of being able to withstand the load in the palmar-dorsal direction. Furthermore, the MP joint can also withstand the load during the radioulnar flexion movement shown in Figure 4B. Note that the term "isosceles triangle" refers not only to a strictly isosceles triangle but also to an approximately isosceles triangle. The area of ​​the triangle relative to the area of ​​the joint support 5 is preferably in the range of 8 to 50%. This allows the pins 6 and 7 to be placed at a certain distance from each other, ensuring stable fixation. The angle between the two sides connecting the center of the bone axis pin 6 and the two palmar pins 7 is preferably in the range of 60 to 120°. The area of ​​the connection between the bone axis pin 6 and the palmar pin 7 and the joint support portion 5 (in other words, the sum of the areas of the double circles of the three pins, i.e., the bone axis pin 6 and the two palmar pins 7 in Figure 3A ) is preferably 4% or more and 30% or less of the area of ​​the joint support portion 5. From the viewpoint of the strength of the pins 6 and 7, the connection area is set to 4% or more. Furthermore, by making the hole drilled in the cortical bone 22 small, i.e., by making the connection area 30% or less, the amount of bone removal can be reduced, thereby preserving the bone strength. In other words, the cortical bone 22 supporting the distal component 2 can be left unremoved. The diameter of the bone axis pin 6 is preferably 1.5 to 3 times the diameter of the palmar pin 7 (or, if not a circle, the length of the diagonal, etc.).

[0044] Furthermore, at least two palmar pins 7 are arranged symmetrically on the flat surface 2b on the rear surface of the joint support 5 with respect to the bone axis 11. This has the effect of supporting the load equally on both sides of the bone axis 11.

[0045] Next, a method for fixing the distal member 2 to the finger bone will be described.

[0046] First, FIG. 5A shows the finger bones to be fixed.

[0047] 5B, a few millimeters of cortical bone 22a on the glenoid cavity side is removed so that the resection surface 22b is approximately perpendicular to the bone axis 11.

[0048] 5C, the bone axis pin 6 is inserted along the bone axis 11 into the cortical bone 22a on the glenoid cavity side and into the medullary cavity 21, and then the palmar pin 7 is inserted into the cortical bone 22a on the glenoid cavity side until the flat surface 2b on the back side of the joint receiving part 5 abuts against the cortical bone 22a on the glenoid cavity side.

[0049] As a result, the distal member 2 is fixed to the articular surface.

[0050] According to the above embodiment, stable fixation can be achieved by the simple method of simply inserting the implant into the bone, and the risk of loosening after implantation can be reduced.

[0051] In other words, in the past, simply increasing the length of the stem inserted into the medullary cavity to stabilize fixation posed the risk of perforating the bone on the opposite side of the joint, or, in the case of a gently curved bone, hitting the cortical bone in the middle of the bone's longitudinal direction, making installation difficult. In contrast, in the above-described embodiment, rather than securing the stem to the cortical bone in the diaphysis of the medullary cavity from the inside, or simply increasing the length of the stem inserted into the medullary cavity to stabilize fixation, the amount of bone resection in the joint area is minimized, and the bone axis pin 6 and the palmar pin 7 are inserted into the cortical bone 22a of the articular surface to achieve stable fixation. Therefore, the sizes of the bone axis pin 6 and the palmar pin 7 can be optimized, preventing unstable fixation of the distal component 2 due to mismatches in size between the medullary cavity 21, the bone axis pin 6, and the palmar pin 7 caused by variations in the medullary cavity 21 of each individual.

[0052] Furthermore, since the bone axis pin 6 is arranged coaxially with the bone axis 11, it is arranged at the center of gravity, thereby improving stability during fixation. In other words, the bone axis pin 6 can be inserted into the cortical bone 22 near the articular surface and fixed, and the fixed bone axis pin 6 is located on the center of gravity axis, thereby further improving stability during fixation.

[0053] Furthermore, since three or more pins, including the bone shaft pin 6 and the palmar pin 7, are arranged non-linearly, greater stability can be achieved with respect to finger movements (e.g., extension-flexion, radioulnar flexion). In this case, when providing three or more pins, an additional pin may be added to the palmar side or the dorsal side.

[0054] In this way, stability during fixation can be improved, and greater stability can be achieved with respect to finger movements (e.g., extension-flexion, radial-ulnar flexion), reducing the risk of loosening after implantation.

[0055] It should be noted that by appropriately combining any of the various embodiments or modifications described above, it is possible to achieve the effects of each. Furthermore, it is possible to combine embodiments with each other, or to combine examples with each other, and it is also possible to combine features of different embodiments or examples. (Note) The following technology is disclosed by the description of the above embodiments. (Technology 1) A distal component of an artificial finger joint, comprising: a joint receiving part that is arranged on the joint surface of the bone and has a spherical concave part that engages with the spherical convex part of the proximal component to allow it to bend freely; a bone axis pin that extends from the joint receiving part along the bone axis and penetrates the cortical bone to be inserted into the medullary cavity; and at least two palmar side pins that extend from the joint receiving part and are insertable into the cortical bone, are shorter than the bone axis pin, and are located on the palm side of the bone axis pin; when the joint receiving part is divided into a palmar half region and a dorsal half region in the palm-dorsal direction, the centers of the at least two palmar side pins are each located in the palmar half region, and the center of the bone axis pin is located in the dorsal half region. (Technology 2) The distal component of an artificial finger joint according to Technology 1, in which, when the joint receiver is divided into two equal halves in the left-right direction perpendicular to the palmar dorsum direction, the at least two palmar pins are located in each of the left and right half regions. (Technology 3) The distal component of an artificial finger joint according to Technology 1 or 2, in which the bone shaft pin is located at the vertex shared by two equal sides of an isosceles triangle, and the at least two palmar pins are located at the remaining two vertices. (Technology 4) The distal component of an artificial finger joint according to any one of Technology 1 to 3, in which the palmar pins each have a cylindrical portion that can be inserted into the cortical bone. (Technology 5) The distal component of an artificial finger joint according to Technology 4, in which each palmar pin has a truncated cone portion at the tip of the cylindrical portion. (Technology 6) The distal side component of the artificial finger joint according to any one of technologies 1 to 5, wherein the thickness of the thinnest part of the spherical recess of the joint receiving portion is 1 mm or less and 0.1 mm or more. (Technology 7) The distal side component of the artificial finger joint according to any one of technologies 1 to 5, wherein the bone shaft pin has a truncated cone shape.(Technology 8) The distal component of an artificial finger joint according to Technology 6, wherein the bone axis pin has a truncated cone shape. (Technology 9) The distal component of an artificial finger joint according to any one of Technology 1 to 8, wherein the length of the bone axis pin is longer than the shortest distance from the end of the joint receiving part to the center of the bone axis pin. (Technology 10) The distal component of an artificial finger joint according to any one of Technology 1 to 9, wherein the difference in size of the joint receiving part in the palmar direction relative to the bone cut surface is 0 mm or more and 1 mm or less. (Technology 11) The distal component of an artificial finger joint according to any one of Technology 1 to 10, wherein when the bone axis pin is placed at one vertex of a triangle in the joint receiving part and the at least two palmar pins are placed at the remaining two vertices, the area of ​​the triangle is in the range of 8 to 50% of the area of ​​the joint receiving part. (Technology 12) The distal side member of the artificial finger joint according to any one of Technologies 1 to 11, wherein the area of ​​the connection portion of the bone shaft pin and the at least two palmar pins to the joint receiving portion is 4% or more and 30% or less of the area of ​​the joint receiving portion. (Technology 13) The artificial finger joint comprising the proximal side member and the distal side member according to any one of Technologies 1 to 12.

[0056] The artificial finger joint portion and its distal member according to the above-described aspect of the present invention can also be used in the joints of fingers or toes, such as the DIP (Distal Interphalangeal) joint, PIP (Proximal Interphalangeal) joint, MP (Metacarpal Interphalangeal) joint, CM (Carpometacarpal) joint, or IP (Interphalangeal) joint of the thumb.

[0057] REFERENCE SIGNS LIST 1 Artificial finger joint portion 2 Distal side member 2a Spherical concave portion 2b Flat surface 2c Thinnest portion 3 Proximal side member 3a Spherical convex portion 5 Joint receiving portion 6 Bone axis pin 7 Palmar pin 7a Circular truncated cone portion 7b Cylindrical portion 11 Bone axis 12 Isosceles triangle 12a, 12b Vertex 21 Medullary cavity 22 Cortical bone 22a Glenoid cavity side cortical bone 22b Resection surface 24 Cancellous bone 300 Bisector 300a Palmar half region 300b Dorsal half region 310 Bisector 310a Left half region 310b Right half region

Claims

1. A distal component of an artificial finger joint comprising: a joint receiving part that is disposed on the joint surface of a bone and has a spherical recess that engages with the spherical convex part of a proximal component to allow it to be freely bent; a bone axis pin that extends from said joint receiving part along the bone axis and penetrates the cortical bone and can be inserted into the medullary cavity; and at least two palmar side pins that each extend from said joint receiving part and can be inserted into the cortical bone, are shorter than said bone axis pin, and are located on the palm side of said bone axis pin, wherein when said joint receiving part is divided in half in the palm-dorsal direction into a palmar half region and a dorsal half region, the centers of said at least two palmar side pins are each located in the palmar half region and the center of said bone axis pin is located in the dorsal half region.

2. The distal member of the artificial finger joint as described in claim 1, wherein when the joint receiving portion is divided into a left half region and a right half region in the left-right direction perpendicular to the palm dorsum direction, the at least two palm side pins are located in the left half region and the right half region, respectively.

3. The distal member of the artificial finger joint as described in claim 1, wherein the bone axis pin is arranged at the vertex shared by two equal sides of an isosceles triangle in the joint receiving portion, and the at least two palmar pins are arranged at the remaining two vertices.

4. The distal component of the artificial finger joint as described in claim 1, wherein each of the palmar pins has a cylindrical portion that can be inserted into the cortical bone.

5. The distal member of the artificial finger joint as claimed in claim 4, wherein each of the palmar pins has a truncated cone portion at the tip of the cylindrical portion.

6. A distal side member of an artificial finger joint as described in any one of claims 3 to 5, wherein the thickness of the thinnest part of the spherical recess of the joint receiving portion is 1 mm or less and 0.1 mm or more.

7. A distal member of an artificial finger joint as described in any one of claims 3 to 5, wherein the bone axis pin is frustoconical in shape.

8. The distal member of the artificial finger joint according to claim 6, wherein the bone shaft pin is frustoconical in shape.

9. The distal member of the artificial finger joint as described in claim 1, wherein the length of the bone axis pin is longer than the shortest distance from the end of the joint receiving portion to the center of the bone axis pin.

10. A distal component of an artificial finger joint as described in claim 1, wherein the difference in size of the joint receiving portion in the palmar direction relative to the bone cut surface is 0 mm or more and 2 mm or less.

11. The distal side component of the artificial finger joint according to claim 1, wherein when the bone axis pin is placed at one apex of a triangle in the joint receiving portion and the at least two palmar pins are placed at the remaining two apexes, the area of ​​the triangle is in the range of 8 to 50% of the area of ​​the joint receiving portion.

12. The distal component of the artificial finger joint as described in claim 1, wherein the connection area of ​​the bone axis pin and the at least two palmar pins to the joint receiving portion is 4% or more and 30% or less of the joint receiving portion.

13. An artificial finger joint comprising the proximal member and the distal member according to any one of claims 1 to 5.

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