Stem for artificial hip joint

Abstract

To provide a stem whose distal end can be inserted without a gap into a hole bored in a femur when the stem is inserted and fixed to the femur.SOLUTION: In a stem for an artificial hip joint whose distal end portion on the insertion side into the femur is approximately bar-shaped, a slit 4 parallel to the longitudinal direction of the stem and piercing through radially is introduced at the distal end portion on the insertion side into the femur.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a stem which is a component of an artificial hip joint, and facilitates the surgical operation of attaching and connecting it to the femur.

Background Art

[0002] An artificial hip joint is an artificial joint that connects the femur and the acetabulum, and can be roughly classified into a stem fixed to the femur side and a cup attached to the acetabulum side. One end 2 of the stem is inserted and fixed inside the femur, and a spherical head 1 is provided at the other end. By inserting this into the cup, the femur and the acetabulum are connected. The cup has a double-shell structure in the shape of a hemispherical shell, mostly with a metal outer shell and a resin inner shell inside. The head provided at the tip of the stem is inserted into the inner shell of the cup, and by rotating within the cup, the femur connected to the head can rotate around the acetabulum. It already has a history of several decades in human applications, and in recent years it has also been applied to animals.

[0003] As shown in FIG. 1, the vicinity of the tip of the portion of the stem inserted into the femur is generally rod-shaped. This is inserted into a hole opened in the longitudinal direction of the femur and connected to the femur. The upper part of the femur is thick, and the thick part following the rod-shaped part of the stem is also inserted into the femur. One of the problems during the connection is that the surgical operation of connecting the stem to the femur is very costly. When attaching the stem to the femur, first, the head portion of the femur is resected, then a hole is drilled longitudinally at the center of the femur, and a generally rod-shaped stem is inserted into this hole from the bone cutting part of the upper part of the femur. After that, the stem is connected to the femur. The femur is originally cylindrical with a longitudinally hollowed hole inside, but this hole is thinner than the femur, so generally this hole is expanded with a rod-shaped file or drill.

[0004] Here, the femur is somewhat curved in the longitudinal direction, and correspondingly, the internal hole is also curved. However, it is difficult to make the stem conform to this shape, and generally it is straight. This is because the curvature situation varies depending on the affected dog. For this reason, it is difficult to drill a hole such that the stem can be inserted into the hole on the inner surface of the femur without any gap. As a result, a hole of a certain size with some margin has to be drilled. As a result, a gap is generated between the stem and the inside of the femur after insertion, that is, play occurs, and dealing with this gap is necessary to connect the stem to the femur.

[0005] There are roughly two methods for connecting the stem to the femur, that is, for dealing with the above-mentioned gap: a mechanical method of fixing with screws, wedges, etc. and a method of pouring cement or the like into the gap and hardening it. Among these, fixing with cement is easy in terms of filling the above-mentioned gap and is widely used. However, in addition to the fact that it takes time for the cement to solidify, there are issues with the reliability of the adhesion strength between the femur and the cement, or between the cement and the stem. There is also a risk of infectious diseases.

[0006] On the other hand, in the case of screw or wedge fixation, the problems of cement fixation are eliminated, but there are issues with the fixation work itself. When fixing with screws or wedges when there is a gap between the stem and the inner surface of the femur, generally the stem needs to be fixed to the femur at at least two points. This is because if only fixed at one point, the stem will rotate in the gap around the fixed point with respect to the femur, that is, play occurs. From the perspective of restraining this rotation, it is better for these two connection points to be separated. One point is taken at a portion near the cut part of the femur at the central part of the stem for ease of operation, and the other point is taken near the tip of the stem away from there.

[0007] Among these, near the central part of the stem, the femur to which it is to be joined is thick, and thus the stem is also large. In addition, since it is close to the cut surface of the femur, that is, the entrance for inserting the stem, it is easy to drive in screws or wedges. However, near the tip of the stem where it joins the femur away from this part, in addition to the femur becoming thinner, since it is away from the cut surface of the femur, that is, the entrance for inserting the stem, the operation of screw fixation or wedge insertion becomes difficult. Especially when applied to children or small animals, etc., since the stem is small and thin, it is difficult to penetrate and fix a screw near the tip of the stem.

Summary of the Invention

Problems to be Solved by the Invention

[0008] In the insertion and connection of the stem to the femur, when the stem is inserted into the femur, it is possible to easily insert the tip portion of the stem against the inner surface of the femur without a gap.

Means for Solving the Problems

[0009] In the stem of an artificial hip joint whose tip portion on the side to be inserted into the femur is generally rod-shaped, the thickness of the tip portion on the side to be inserted into the femur is made to be elastically variable. As a specific structure, a cut is provided in a portion of a certain length at the tip of the stem, which is generally parallel to the longitudinal direction of the stem and penetrates in the radial direction.

Effects of the Invention

[0010] As shown in Fig. 2, when a longitudinal notch 4 is introduced at the stem tip, the remaining portion 5 becomes a cantilever beam and can be plastically deformed in the radial direction of the stem. That is, by applying a radial force to the tip of this beam 5, the thickness of the stem tip portion can be elastically changed. Therefore, the diameter of the hole drilled in the femur is made slightly smaller than the diameter of the stem tip portion, and when the stem is pushed in with a certain force, the above-mentioned beam is elastically bent and deformed in the central axis direction, and the diameter of the stem tip becomes smaller and is inserted into the femur. As a result, there is no gap between the femur and the stem tip always presses against the inner surface of the femur. If the bending rigidity of this beam 5 is adjusted within an appropriate range, the rotation of the stem within the femur can be restricted, that is, coupled, within a practically problem-free range. The adjustment of the bending rigidity can be easily adjusted by the length of the notch portion, the width of the notch, etc. If the hole drilled in the femur becomes larger than the stem tip portion, a conical wedge or the like is pushed into the stem tip, and the stem tip is plastically expanded in the radial direction so that the stem tip can be made thicker than the hole in the femur in the natural state before insertion. This operation can be easily performed even at the surgical site. As a result, when drilling a hole for inserting the stem into the femur, it is only necessary to drill it once using a drill bit or a file slightly smaller than the stem tip, and there is no need to finely adjust it several times little by little as in the conventional method, and the working time can be significantly shortened.

[0011] However, in the conceptual diagram shown in Fig. 2, the diameter of the hole drilled in the femur needs to be made smaller only at the tip of the stem. This is because if the hole drilled in the femur is thin from the entrance to the tip of the stem, the part of the stem without a notch cannot be inserted. One solution is to make the hole in the femur conical at the part where the tip of the stem is located using a drill with a tapered tip or the like, and insert the tip of the stem into this conical part. It is necessary to manage the position of the conical part to be near the tip position of the stem. On the other hand, if the tip of the stem is plastically expanded in advance by inserting a wedge or the like, a hole thicker than the tip part of the stem can be drilled through the femur from the entrance, and the insertion operation of the stem becomes easier. As an application of this, as shown in 6 of Fig. 3, if the tip of the stem is made thicker than the part without a notch and made into a rotational ellipsoidal shape, the prior plastic deformation operation becomes unnecessary, smoother insertion becomes possible, and the coupling operation of the stem becomes even easier.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

Examples

[0013] Figure 4 shows the overall shape of the embodiment. There are four cuts at the tip, and the maximum diameter is about 15% larger than the part without cuts. A screw hole 7 is provided in the middle of the stem, and the stem is coupled to the femur by passing a through screw from the outside of the femur. If a hole slightly larger than the part of the stem without cuts is made on the femur side, the stem can be inserted while being stretched inside the femur by pushing it in with a certain force, and the tip can always be inserted without a gap between the femur. As a result, the stem is fixed to the femur at two points, namely the screw part and the tip. Note that the upper part of this stem has a jaw 8 protruding in a direction perpendicular to the longitudinal direction of the stem. This jaw is designed to hit the upper end cut surface of the femur, that is, the edge of the insertion entrance, when the stem is inserted into the femur. Most of the force acting on the femur is due to the patient's body weight and acts downward in the longitudinal direction of the femur. Therefore, this jaw plays a role of transmitting the main force acting on the femur to the femur. According to the present invention, since the position of the stem tip can contact the femur without a gap even if it moves slightly, this jaw can be easily applied to the edge of the stem.

Explanation of Reference Numerals

[0014] 1 Bone part of the stem 2 Schematic rod-shaped part inserted into the femur of the stem 3 Tip part of the stem (the part targeted by the present invention) 4 Cut part of the tip part of the stem 5 Cantilever beam generated by the cut 6 Thick diameter part of the stem tip 7 Screw hole for fixing the stem 8 Jaw of the stem

Claims

【Claim 1】 In a stem of an artificial hip joint in which the tip portion on the side to be inserted into the femur is generally rod-shaped, a cut is provided in a portion of a certain length in the longitudinal direction from the tip on the side to be inserted into the femur, the cut being generally parallel to the longitudinal direction of the stem and penetrating in the radial direction, so that the thickness of the tip portion on the side to be inserted into the femur can be elastically changed. The thickness of the tip portion having the cut penetrating in the radial direction is larger than that of the generally rod-shaped portion excluding the tip portion having the cut. The thickness of the tip portion is larger than the inner diameter of the hole drilled in the femur for inserting and fixing the stem. An artificial hip joint stem characterized by this.

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