JP2012065940A - Stem for artificial hip joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stem for an artificial hip joint with the structure that a neck is prevented from being tilted relative to a stem body, that fine movements are prevented from arising in the area where the neck is fitted with the stem body and that the neck is changeable.SOLUTION: The stem for an artificial hip joint (a stem 1) includes a stem body 2 to be buried into thighbone and a neck 3 fitted in a concavity 5 formed on the top end of the stem body 2. The end of the neck 3 is provided with a fitting part 4 which includes a fitting part 4b that is in parallel with its opposite surface in addition to a tapered fitting part 4a. Similarly, the concavity 5 of stem body 2 (the fitted part) is made to be the one which includes a fitted part 5b that is in parallel with its opposite surface in addition to a tapered fitted part 5a.

Description

  The present invention relates to an artificial hip joint stem that is implanted in the proximal portion of a femur.

  Conventionally, surgery (THA: Total Hip Arthroplasty) to replace a hip joint that has been damaged to a state where conservative treatment cannot be performed due to a disease or injury of the hip joint with an artificial hip joint has been performed. An artificial hip joint is mainly composed of three components (parts): a stem, a head ball, and a acetabular cup.

  Here, in order to facilitate fine adjustment of the length of the lower limbs and prevention of interference (impingement) between components, the stem body member embedded in the femur and the neck member to which the head ball is attached are separated. Stems have been developed (for example, Patent Documents 1 to 8). Neck members having a plurality of sizes and shapes are prepared, and a neck member most suitable for the patient is selected from these, and fitted to the stem body member.

US Pat. No. 4,957,510 US Pat. No. 4,822,370 US Pat. No. 6,383,225 US Pat. No. 5,653,764 US Pat. No. 5,135,529 US Pat. No. 6,464,728 Japanese Patent No. 4328911 Japanese National Patent Publication No. 10-502284

  In the stems described in Patent Documents 2 to 6, the fitting portion between the stem main body member and the neck member is tapered. Here, it is desirable that the fitting portion between the stem body member and the neck member hit the entire surface. However, it is difficult to manage the dimensions of the tapered shape in the production of the stem body member and the neck member (the degree of processing difficulty is high). Therefore, even if the fitting part between the stem body member and the neck member is designed to hit the entire surface, the contact state (fitting location) changes depending on the combination of the stem body member and the neck member due to manufacturing errors. May end up.

  Here, in order to realize the contact state (fitting part) intended by the designer, for example, as shown in FIG. 7, as shown in FIG. 7, the back side of the tapered concave portion 105 formed at the distal end portion of the stem body member 102 ( The fitting portion between the stem main body member 102 and the neck member 103 is designed so that the taper portion 104 of the neck member 103 abuts at the bottom (fitting portion P), or the stem main body member as shown in FIG. The stem body member 202 and the neck member 203 are arranged so that the taper portion 204 of the neck member 203 abuts (near the opening) near the tapered concave portion 205 formed at the front end portion of the 202 (fitting portion P). It is conceivable to design a fitting part. Thereby, it can avoid that the fitting location P of a stem main body member and a neck member changes. In addition, it is good also considering the fitting location P of a stem main body member and a neck member as an intermediate position of a taper part.

  However, this method also has problems. As shown in FIGS. 7 and 8, a gap G is generated between the stem body member and the neck member on the opposite side of the fitting portion P. The problem due to the gap G will be described with reference to FIG. 9, taking the back-end type stem main body member 102 and neck member 103 shown in FIG. 7 as an example. The fitting of the neck member 103 to the stem body member 102 is normally performed by driving the tapered portion 104 of the neck member 103 into the recess 105 of the stem body member 102 with a hammer. When the neck member 103 is driven and fitted into the stem body member 102 with a hammer, it is difficult to adjust the angle of the neck member 103 with respect to the stem body member 102. This is because, as shown in FIG. 9, the size of the gap between the B1 portion and the B2 portion is often different each time. In some cases, the neck member 103 is fixed substantially at the center, but the neck member 103 is often fixed while being offset toward the upper side (indicated by a dotted line) or the lower side (indicated by a solid line).

  If the neck member 103 is fixed on the upper side, a load is applied to the neck member 103 in the vertically downward direction, so that the neck member 103 eventually moves downward. On the other hand, when the neck member 103 is fixed to the lower side, the neck member 103 is more stable than when the neck member 103 is fixed to the upper side. However, if the load applied to the neck member 103 fluctuates due to walking or the like, fine movement occurs between the fitting portions of the neck member 103 and the stem main body member 102, and the fitting force between the neck member 103 and the stem main body member 102 decreases. Metal wear may occur between the neck member 103 and the stem body member 102.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to prevent the neck member from being inclined with respect to the stem body member and to occur between the fitting portions of the neck member and the stem body member. It is an object of the present invention to provide an artificial hip joint stem having a structure capable of preventing fine movement and capable of changing a neck portion.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have prevented the neck member from being inclined by providing a parallel fitting portion whose opposing surfaces are parallel, in addition to the tapered fitting portion having a tapered shape. It was found that fine movement between the fitting portion between the neck member and the stem body member can be prevented. Based on this finding, the present invention has been completed.

  That is, the present invention is an artificial hip joint stem comprising a stem body member embedded in a femur and a neck member fitted in a recess formed in an upper end portion of the stem body member. The fitting portion formed at the end of the neck member has a tapered fitting portion having a tapered shape, and a parallel fitting portion having parallel surfaces facing each other, and the recess of the stem body member is It is a stem for an artificial hip joint having a tapered fitting portion with a taper shape into which the tapered fitting portion is fitted, and a parallel fitting portion with which the parallel fitting portion is fitted.

  The taper-shaped taper fitting portion plays a role of securing the fitting force. On the other hand, the parallel fitting portion that is less prone to manufacturing errors (high manufacturing accuracy can be obtained) serves as a guide for the neck member and is a fitting portion as a combined fitting effect with the taper fitting portion. Suppresses microtremors that occur between them. That is, according to the above configuration, apart from the taper fitting portion, there is a parallel fitting portion whose opposing surfaces are parallel, so that when the neck member is fitted to the stem body member, the parallel fitting portion serves as a guide, The neck member can be prevented from tilting. Further, the neck member is restrained to an appropriate degree with respect to the stem body member by the taper fitting portion and the parallel fitting portion that is unlikely to cause a manufacturing error, and thus the fine movement of the neck member can be prevented.

  In the present invention, the taper fitting portion and the taper fitted portion are formed so as to abut on the end portions on the side away from the parallel fitting portion and the parallel fitted portion. It is preferable.

  According to this structure, the parallel fitting part which a manufacturing error does not produce easily is provided in the opposite side (separated side) of the fitting part (contact part) in a taper fitting part. By taking the distance between the fitting part and the parallel fitting part in the taper fitting part, the neck member is inclined with respect to the stem body member, and occurs between the fitting part between the neck member and the stem body member. Fine movement can be further suppressed.

  Furthermore, in this invention, the said fitting part of the said neck member has the said parallel fitting part and the said taper fitting part in an order from the end of the said neck member, and the said recessed part of the said stem main body member is the said recessed part. In order from the bottom side, the parallel mating portion and the taper mating portion are provided, and the taper fitting portion and the taper mating portion are cross-sectionally embedded in the femur. It is preferable that the oval shape is long in the outer direction, and the parallel fitting portion and the parallel fitted portion are circular in cross section.

  According to this configuration, the cross section of the taper fitting portion is formed in an oval shape that is long in the inner and outer directions in a state where the taper fitting portion is embedded in the femur. This increases the section modulus, and improves the strength of the fitting portion between the neck member and the stem body member. The improvement in the strength of the fitting portion contributes to suppression of fine movement generated between the fitting portions of the neck member and the stem main body member. Moreover, it becomes easy to process by making the cross section of a parallel fitting part and a parallel fitting part circular, and the manufacture precision of a parallel fitting part and a parallel fitting part improves. As a result, the neck member is inclined with respect to the stem body member, and fine movement that occurs between the fitting portions of the neck member and the stem body member can be further suppressed.

  According to the present invention, it is possible to prevent the neck member from being inclined with respect to the stem body member, and it is also possible to prevent fine movement that occurs between the fitting portions of the neck member and the stem body member. Further, since it is not necessary to tighten the accuracy of the fitting portion between the stem main body member and the neck member unlike the conventional taper fitting, the manufacturing cost can be reduced. Although the fitting maintenance force between the stem main body member and the neck member is similar to that of the conventional product, the neck member is prevented from being finely moved by the parallel portion, so that the neck member can be prevented from being dropped or damaged.

It is the front view and side view which show the stem for artificial hip joints provided with the fitting structure which concerns on 1st Embodiment of this invention. It is detail drawing which shows the fitting part of the stem for artificial hip joints shown in FIG. It is a figure which shows the modification of the fitting structure shown in FIG. It is a figure which shows the fitting structure which concerns on 2nd Embodiment of this invention. It is a figure which shows the modification of the fitting structure shown in FIG. It is a figure which shows the modification of the fitting structure shown in FIG. It is a figure which shows the fitting structure devised in the middle stage until this invention is completed. It is a figure which shows the fitting structure devised in the middle stage until this invention is completed. It is a figure for demonstrating the problem of the fitting structure shown in FIG.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. An artificial hip joint is mainly composed of three components (parts): a stem, a head ball, and a acetabular cup. The stem is a metal part whose one end is embedded in the medullary vagina of the femur. The head ball is a part attached to the end of the stem. The acetabular cup is a two-layered component having an inner hemispherical shell member excellent in wear and is attached to the acetabular pelvis. The head ball slides with the inner surface of the inner hemispherical shell member of the acetabular cup at its spherical surface. The present invention relates to a stem among these components for an artificial hip joint.

(First embodiment)
FIG. 1 (a) is a front view of an artificial hip joint stem 1 (hereinafter referred to as “stem 1”) having a fitting structure according to the first embodiment of the present invention, and FIG. It is the side view.

  As shown in FIG. 1, the stem 1 includes a stem body member 2 embedded in the femur and a neck member 3 fitted in a recess 5 formed in the upper end portion of the stem body member 2. The stem body member 2 and the neck member 3 are made of a metal such as a titanium alloy, a cobalt chromium alloy, or stainless steel that has been approved for use in living body implantation. The stem body member 2 has a shape that gradually becomes thinner from the proximal portion side to the distal portion side in a state of being embedded in the femur. A head ball (not shown) is attached to the end of the neck member 3 opposite to the stem body member 2.

  A fitting structure between the neck member 3 and the stem body member 2 will be described with reference to FIG. 2A is an enlarged cross-sectional view of a portion X in FIG. 1A, and FIG. 2B is a cross-sectional view taken along line AA in FIG.

(Neck member)
As shown in FIG. 2, a fitting portion 4 for fitting into the concave portion 5 of the stem body member 2 is formed at the end of the neck member 3. This fitting part 4 consists of the taper-shaped taper fitting part 4a and the parallel fitting part 4b in which the opposing surface is parallel. The taper fitting part 4a is provided at one end of the neck member 3, and the parallel fitting part 4b is provided continuously to the taper fitting part 4a toward the other end side (the head ball mounting side) of the neck member 3. ing. In addition, the boundary between the taper fitting portion 4a and the parallel fitting portion 4b is shown in FIG. 2A as an angle change point Q (Note that the boundary between the taper fitting portion 4a and the parallel fitting portion 4b is a fitting point). It exists over the entire circumferential direction of the joint portion 4). The center line C of the taper fitting part 4a and the center line C of the parallel fitting part 4b coincide.

  As shown in FIG. 2B, the cross sections of the taper fitting portion 4a and the parallel fitting portion 4b have an oval shape that is long in the inner / outer direction when the stem body member 2 is embedded in the femur. Is formed. The oval shape means a shape composed of a set of parallel lines and two semicircular lines that are located on both sides of the set of lines and connect the sets of lines. The cross sections of the taper fitting portion 4a and the parallel fitting portion 4b may be elliptical or circular (cross-sectional shapes of a taper fitted portion 5a and a parallel fitted portion 5b described later). The same applies to.

(Stem body member)
The concave portion 5 formed in the upper end portion of the stem body member 2 is fitted with a tapered tapered fitting portion 5a into which the tapered fitting portion 4a of the neck member 3 is fitted and a parallel fitting portion 4b of the neck member 3 is fitted. It consists of parallel mating parts 5b. The taper fitted portion 5a is provided on the bottom side of the concave portion 5, and the parallel fitted portion 5b is provided on the opening side of the concave portion 5 continuously to the taper fitted portion 5a. The boundary between the taper fitted portion 5a and the parallel fitted portion 5b is shown in FIG. 2A as the angle change point R (Note that the taper fitted portion 5a and the parallel fitted portion 5b The boundary exists over the entire circumferential direction of the fitting portion 4). The center line C of the taper fitted portion 5a and the center line C of the parallel fitted portion 5b coincide.

  The cross sections of the tapered fitted portion 5a and the parallel fitted portion 5b are formed so as to have an oval shape that is long in the inner and outer directions in a state where the stem body member 2 is embedded in the femur.

  Here, the inclination angle of the inner wall surface of the taper fitting portion 5a is made slightly larger than the inclination angle of the outer surface of the taper fitting portion 4a, and the taper fitting portion 4a of the neck member 3 and the taper of the stem body member 2 are made. The neck member 3 and the stem body member 2 are designed so that the fitted portion 5a is fitted at the end of the taper fitting portion 4a (the bottom side of the recess 5) (fitting location P) (note that FIG. 2A is a cross-sectional view, so that the fitting portion is illustrated as a dot, but the fitting between the taper fitting portion 4a and the taper fitted portion 5a is the entire circumferential direction of the fitting portion. (The same applies to other embodiments and modifications)). Moreover, the parallel fitting part 4b and the parallel to-be-fitted part 5b are provided in the other side (separated side) of this fitting location P (contact location). The parallel fitting portion 4b and the parallel fitted portion 5b are an intermediate fit. It should be noted that the parallel fitting portion 4b and the parallel fitted portion 5b are easy to perform dimensional management because the opposing surfaces are parallel, in other words, production errors are unlikely to occur (high production accuracy can be obtained).

(Surgery technique)
After cutting the femoral head, the femoral bone marrow vagina is opened using a surgical file or the like. Then, after preparing the medullary vagina of the femur, the stem body member 2 is placed on the medullary vagina of the femur while being appropriately hit with a surgical hammer. Thereafter, an appropriate neck member 3 and a head ball are selected using a neck trial, and the neck member 3 is inserted into the recess 5 of the stem body member 2. Then, a special instrument is set on the head of the neck member 3, and the neck member 3 is fitted to the stem body member 2 while hitting the special instrument with a surgical hammer.

  According to the stem 1 (prosthetic hip joint stem) of the present embodiment, apart from the taper fitting portion 4a, there is a parallel fitting portion 4b whose opposing surfaces are parallel, so that the neck member 3 is hammered on the stem body member 2. The parallel fitting portion 4b serves as a guide when the fitting is performed, and the neck member 3 can be prevented from being inclined. Further, the neck member 3 is restrained to an appropriate degree with respect to the stem body member 2 by the taper fitting portion 4a and the parallel fitting portion 4b in which production errors are unlikely to occur (high production accuracy can be obtained). Can be prevented. That is, the fitting of the neck member 3 to the stem body member 2 is stable.

  Moreover, in the stem 1, the parallel fitting part 4b which a manufacturing error does not produce easily is provided in the opposite side (separated side) of the fitting place P (contact part) in the taper fitting part 4a. Thus, the neck member 3 is inclined with respect to the stem body member 2 and the neck member 3 and the stem by taking the distance between the fitting portion P and the parallel fitting portion 4b in the taper fitting portion 4a. Fine movement occurring between the fitting parts with the main body member 2 can be further suppressed.

  Further, the weight of the person is mainly applied to the fitting portion in the inner and outer directions. By making the cross section of the fitting portion 4 into an oval shape that is long in the inner and outer directions in a state of being embedded in the femur, the cross section coefficient of the fitting portion 4 is larger than in the case of a circular form with the same area. Thus, the strength of the fitting portion between the neck member 3 and the stem body member 2 is improved. The improvement of the strength of the fitting portion contributes to suppression of fine movement generated between the fitting portions of the neck member 3 and the stem body member 2.

(Modification of the first embodiment)
FIG. 3 shows a stem body member 22 and a neck member 23 according to a modification of the first embodiment.
The difference between this modified example and the first embodiment is that the positional relationship between the tapered fitting part (or tapered fitted part) and the parallel fitting part (or parallel fitted part) is the first in this modified example. This is the opposite of the embodiment. Below, the difference between this modification and 1st Embodiment is explained in full detail. Note that a description of the same configuration as that of the first embodiment is omitted.

  As shown in FIG. 3, the parallel fitting portion 24b of the neck member 23 is provided at one end of the neck member 23 (fitting portion 24), and the taper fitting portion 24a is continuous with the parallel fitting portion 24b. The neck member 23 is provided toward the other end side. Similarly, the parallel fitted portion 25b of the stem body member 22 is provided on the bottom side of the concave portion 25, and the tapered fitted portion 25a is provided on the opening side of the concave portion 25 continuously to the parallel fitted portion 25b. It has been.

  In this modification, the inclination angle of the inner wall surface of the tapered fitting portion 25a is slightly smaller than the inclination angle of the outer surface of the taper fitting portion 24a, and the taper fitting portion 4a of the neck member 23 and the stem body member 22 are formed. The neck member 23 and the stem body member 22 are designed so that the taper fitted portion 25a is fitted to the end portion of the taper fitting portion 24a (opening portion of the recess 25) (fitting portion P). .

  Although not shown, the cross sections of the taper fitting portion 24a and the parallel fitting portion 24b are oval in the inner and outer directions with the stem body member 22 embedded in the femur as in the first embodiment. It is formed so as to have a shape (the same applies to the tapered fitted portion 25a and the parallel fitted portion 25b).

(Second Embodiment)
A fitting structure according to the second embodiment will be described with reference to FIG. In this embodiment, the cross-sectional shape of the fitting part 34 of the neck member 33 (and the recessed part 35 which is a to-be-fitted part formed in the stem main body member 32) is divided into an oval shape and a circular shape. Fig.4 (a) is front sectional drawing which shows a fitting structure, FIG.4 (b) is AA sectional drawing of Fig.4 (a). In addition, regarding this embodiment, description is abbreviate | omitted about the structure similar to embodiment and modification which were demonstrated previously (it is the same also about the modification mentioned later).

(Neck member)
As shown in FIG. 4, one end of the neck member 33 is provided with a parallel fitting portion 34 b having a circular cross section. Further, a tapered fitting portion 34a having a cross section is provided continuously to the parallel fitting portion 34b toward the other end side (the head ball mounting side) of the neck member 33. The longitudinal direction of the oval shape is the direction that coincides with the inside-outside direction (in other words, the direction in which a person's weight is added) in a state where the stem is embedded in the femur.

  As shown in FIG. 4B, regarding the cross-section of the oval shape of the taper fitting portion 34a at the boundary between the taper fitting portion 34a and the parallel fitting portion 34b, the dimension in the minor axis direction (of the oval shape). The width dimension) is made to coincide with the diameter of the parallel fitting portion 34b (the same applies to the boundary between the tapered fitted portion 35a and the parallel fitted portion 35b described later).

(Stem body member)
The parallel fitted portion 35b of the stem body member 32 is provided on the bottom side of the recessed portion 35, and the tapered fitted portion 35a is provided on the opening side of the recessed portion 35 continuously to the parallel fitted portion 35b. . The cross section of the parallel fitted portion 35b is circular, and the cross section of the tapered fitted portion 35a is an oval shape that is long in the inner and outer directions with the stem embedded in the femur.

  According to the fitting structure according to the present embodiment, when the cross section of the taper fitting portion 34a is formed in an oval shape that is long in the inner and outer directions in a state of being embedded in the femur, In comparison, the section modulus is increased, and the strength of the fitting portion between the neck member 33 and the stem body member 32 is improved. The improvement in the strength of the fitting portion contributes to suppression of fine movement generated between the fitting portions between the neck member 33 and the stem main body member 32. Moreover, it becomes easy to process by making the cross section of the parallel fitting part 34b and the parallel fitting part 35b circular, and the manufacture precision of the parallel fitting part 34b and the parallel fitting part 35b improves. As a result, the neck member 33 is inclined with respect to the stem body member 32, and the fine movement generated between the fitting portions between the neck member 33 and the stem body member 32 can be further suppressed.

(First Modification of Second Embodiment)
A first modification of the fitting structure according to the second embodiment will be described with reference to FIG. The main difference between the present modification and the second embodiment is that the tapered fitting portion (or tapered fitting portion) having an oval cross section and the parallel fitting portion (or parallel fitting portion) having a circular cross section. In this modification, the positional relationship is reversed from that of the second embodiment. Fig.5 (a) is front sectional drawing which shows a fitting structure, FIG.5 (b) is AA sectional drawing of Fig.5 (a).

  As shown in FIG. 5, the taper fitting portion 44a of the neck member 43 is provided at one end of the neck member 43 (fitting portion 44), and the parallel fitting portion 44b is continuous with the taper fitting portion 44a. The neck member 43 is provided toward the other end side. Similarly, the taper fitted portion 45a of the stem body member 42 is provided on the bottom side of the recess 45, and the parallel fitted portion 45b is provided on the opening side of the recess 45 continuously to the taper fitted portion 45a. It has been. The cross section of the taper fitting portion 44a has an oval shape portion 44a1 and a circular portion 44a2, and as shown in FIG. 5A, the fitting portion P is shown, the taper fitting portion 44a and the taper fitted portion 45a. Is fitted (contacted) at the oval shape. It is not always necessary to divide the cross section of the taper fitting portion 44a into the oval shape portion 44a1 and the circular portion 44a2, and the entire cross section of the taper fitting portion 44a may be oval shape or a shape such as a circle. Also good.

  As shown in FIG. 5B, in the taper fitting portion 44a, the cross-section of the oval shape portion 44a1 at the boundary between the oval shape portion 44a1 and the circular portion 44a2 is the dimension in the major axis direction (oval shape). The length dimension of the shape is made to coincide with the diameter of the circular portion 44a2.

(Second Modification of Second Embodiment)
A second modification of the fitting structure according to the second embodiment will be described with reference to FIG. The main difference between the present modification and the second embodiment is that the taper fitting portion 34a in the second embodiment has an oval shape in all cross sections, whereas the neck member 53 in the present modification is different. The taper fitting portion 54a is a point composed of an oval cross-sectional portion 54a1 and a circular cross-sectional portion 54a2. The circular cross-sectional portion 54a2 of the taper fitting portion 54a is located in the opening of the recess 55 of the stem body member 52, and the oval cross-sectional portion 54a1 is located in the back thereof.

  In addition, the structure of the parallel fitting part 54b of the fitting part 54 which concerns on this modification, and the taper to-be-fitted part 55a and the parallel to-be-fitted part 55b of the recessed part 55 is the same as that of what concerns to 2nd Embodiment corresponding. It is a configuration.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made as long as they are described in the claims. .

1: stem for artificial hip joint 2: stem body member 3: neck member 4: fitting portion 4a: taper fitting portion 4b: parallel fitting portion 5: recessed portion 5a: tapered fitting portion 5b: parallel fitting portion

Claims (3)

A stem for an artificial hip joint, comprising: a stem body member embedded in the femur; and a neck member fitted in a recess formed in the upper end portion of the stem body member,
The fitting portion formed at the end of the neck member is
A taper fitting portion with a taper shape;
A parallel fitting portion whose opposing faces are parallel, and
Have
The recess of the stem body member is
A taper-fitting portion having a tapered shape into which the taper fitting portion is fitted; and
A parallel mating portion into which the parallel fitting portion is fitted, and
A stem for an artificial hip joint. The stem for an artificial hip joint according to claim 1,
The taper fitting portion and the taper fitted portion are formed so as to abut on the parallel fitting portion and the end portion on the side away from the parallel fitted portion. , Stem for artificial hip joint. The stem for an artificial hip joint according to claim 2,
The fitting portion of the neck member has the parallel fitting portion and the taper fitting portion in order from the end of the neck member,
The concave portion of the stem body member has the parallel fitted portion and the tapered fitted portion in order from the bottom side of the concave portion,
The cross sections of the taper fitting portion and the taper mated portion are oval in a state of being embedded in the femur in the inner and outer directions, and the cross sections of the parallel fitting portion and the parallel mated portion are A stem for an artificial hip joint, characterized by being circular.

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