JPH01136654A - Preparation of acetabular socket - Google Patents

Abstract

PURPOSE:To form an acetabular socket not generating distortion and damage at all and having extremely high reliability, by arranging a large number of projections to a socket backed by a metal and holding a plastic body formed of HDP plastic to extremely low temp. to insert the same under pressure at the ambient temp. CONSTITUTION:In a method for preparing an acetabular socket consisting of the outer frame body fixed to the hipbone by cement and a plastic body wherein a condyle sphere is held to the outer frame body in a freely slidable manner, when a plastic main body 1 is cooled by liquid nitrogen, the HDP plastic main body can be easily inserted in the socket 2, wherein projections each having a height of 0.6mm are arranged to the inside thereof on the circumference circle thereof, under pressure. The HDP plastic main body 1 expands at the ambient temp. and the projections of the socket 2 are penetrated in the soft HDP plastic main body to develop fall-out preventing action. Pressure is removed to take out the whole from a jig and sterilization treatment by the irradiation with gamma-rays of 2.5MR is performed to prepare the acetabular socket.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing an acetabular socket, which is used as an acetabular socket with good sliding properties and rigidity for artificial hip joints, knees, etc. It is something that will be done.

(Prior art) As a prior art related to the present invention, Japanese Patent Application Laid-Open No. 58-20645
There is a public notice of issue.

This is the artificial hip joint shown in Figures 5 and 6.
The socket 11 has a ceramic hack 12 which is an outer frame made of a material with high mechanical strength such as alumina ceramics, and this socket has a groove 13 for fixing it in the living bone and a flange at the peripheral end. The portion 14 is integrally formed.

In this way, polyethylene is press-fitted as a plastic body 17 into the substantially hemispherical recess 15 of the ceramic back 12 of ceramics by injection molding and physically fixed, and molded to form a good sliding surface 19 with the femoral head ball 18. It is processed.

An undercut type recess 20 is formed in the hemispherical recess 15 of the ceramic back 12, and a part of the plastic body 17 is press-fitted into the recess 20 to form an undercut 21. An acetabular socket 11 from which the body 17 is difficult to detach is formed.

(Problems to be Solved by the Invention) However, the acetabular socket is: (1) The plastic body 17 is press-fitted from polyethylene by injection molding, but since polyethylene has large thermal expansion and contraction, After molding and solidification, a large shrinkage occurs, and a gap 16 is formed at the interface between the ceramic back 12 and the plastic body 17, and the gap is as large as 0.5** in some places. This is because when a load is applied during use, it becomes loose as shown in FIG. 6, resulting in a large gap 16.

(2) In addition, if such a gap is created and loosening occurs when a load is applied, the friction characteristics with the opposing bone head will deteriorate such as uneven wear, and (3) - Living environment on a boat. At the bottom, a load is applied to the pelvis from the center of the femoral head toward the sacroiliac joint, and the femoral head is supported by two places, the sacroiliac joint and the symphysis pubis.In the case of an artificial hip joint, this is shown at position 22 in Figure 5. It is thought that high stress areas are spread over a wide area, and in particular, because there is an undercut type recess, high stress concentration at position 22 will have a negative impact on the wear characteristics, and furthermore, fatigue due to repeated loading will cause the plastic body to break away from the stress concentration area. There are problems such as 17 damage is easy to occur.

The technical problem of the present invention is to provide a method for manufacturing an acetabular socket used in an artificial hip joint, which has no gap between the socket and the plastic body and has good sliding and rigidity. It is.

[Structure of the invention]

(Means for solving the problems) The technical measures taken to solve the above technical problems are as follows. That is, in a method for manufacturing an acetabular socket, which is made of an outer frame that is fixed to the hip bone with cement or the like, and a plastic body that holds a slidable femoral ball on the outer frame,
The plastic body was molded with ultra-high molecular weight polyethylene and then cooled and shrunk using liquid nitrogen, etc., and then a plurality of protrusions were arranged on the inner peripheral surface of the outer frame made of titanium, stainless steel, or ceramics, and then cooled and shrunk. The acetabular socket is manufactured by press-fitting the plastic body into the outer frame at room temperature.

(Operation) The technical means operates as follows. That is, a large number of protrusions are placed in the socket of the metal back 1, a plastic body made of HDP plastic is held at an extremely low temperature,
When the HDP plastic is compressed by about 1 mm in diameter and press-fitted at room temperature, the HDP plastic expands and the protrusions bite into the soft HDP to securely fix it.
The P plastic body has extremely good sliding properties, so the femoral head can rotate freely, and there is no gap between the HDP plastic and the metal back, so it does not bend or break even after many years of use. It is a highly reliable acetabular socket.

(Example) Examples will be described below.

When molding an acetabular socket using conventional hot press compression molding, ultra-high molecular weight polyethylene shrinks considerably when it returns to room temperature after molding, but as shown in this example, a method opposite to the conventional method was used. I] Large thermal expansion and contraction of DP (
approximately 1.6 x 10-'/'c) and liquid helium temperature (
We will describe a method for making an acetabular socket made of HDP plastic and a socket (back metal, etc.) by cryogenic cold fitting, taking advantage of the fact that it does not lose its properties up to -269°C.

Figure 1 shows the acetabular socket according to this embodiment attached to an artificial hip joint, where 1 is an HDP plastic body, 2 is an outer frame made of titanium, stainless steel, or ceramics, and 4 is a part of the hip joint. , 3 is cement that fixes the hip joint and the socket, and 5 is the femoral ball.

FIG. 4 shows an example of the shape of the conventional artificial acetabular socket for cement fixation, and the plastic body shown at 1 in FIG. 2 is made of HDP plastic with a molecular weight of 4 million and is molded by compression molding or cutting. The second dimension in the diagram is 33.
6mm, one dimension is 3411. Figure 3 shows an outer frame made of ceramics such as titanium, stainless steel or alumina, with protrusions 2a, 2b, etc. on the inside upper part of the semicircular shape.
・If provided on the circumference or two protrusions covering the entire circumference of the inner circumferential surface, the dimension between the protrusions b = 32.4 x II
The height of the protrusion is set to 0.6 +u.

The assembly and installation of the plastic body 1 and the socket 2 will be explained.

(1) When cooled with plastic body 1 and liquid nitrogen <-196℃), 33.6X220X1.6X10-'-1
, 18, the diameter is thought to shrink by about 1.18 mm.

In this case, the liquid nitrogen is -196°C and the room temperature is about 24°C, and this difference of 220°C was calculated as the temperature difference.

Projections with a height of 0.61111 mm are arranged on the circumference inside the socket 2, and while the socket 2 remains at room temperature, the HDP plastic body 1 is placed in a pot containing liquid nitrogen and cooled sufficiently. Leave the outer frame at room temperature.

(When the temperature of the 21HDP plastic body I reaches -196°C, the outer diameter shrinks by 1.2 fins, and the center axis of each body is press-fitted with a jig so that it becomes coaxial with the inner diameter surface of the outer frame 2. In this case, the dimensions of the plastic body a shrink to 3
2.4 mm, and the dimension between the protrusions of socket 2 is 3
The HD P plastic body 1 can be easily press-fitted into the socket 2 due to the 2.4 mm.

At room temperature, the HDP plastic body 1 expands, and as shown in FIG. 4, the protrusion of the socket bites into the soft HDP plastic body to prevent it from being pulled out.

(3) Remove the press-fitting pressure and take it out from the jig, for example,
2.5MRads (Mega, RaF) Acetabular sockets are manufactured by performing sterilization treatment using 77-ray irradiation.

FIG. 7 shows a comparison of the fitting strength between the case where the HDP plastic and the metal back were manufactured by hot pressing and the case of this example.

In Figure 7, a metal back 2 with a height of 0.6 mm x width of 1.0 yn is placed inside the metal back 2 made of stainless steel.
The flange 1a is provided, and the HDP plastic is cold-fitted to A, and the protrusion 2a inside the metal back,
2'b, . If C is a socket molded using a hot press method, the fitting strength between the socket and HDP plastic is 400 to 500 kg for A and B, as shown in the graph in Figure 7.
In contrast, C of the conventional example weighs about 100 kg, and C also has Q, 5 ina at the interface between the HDP part and the socket.
There was a gap between the two.

As described above, the difference in fitting strength between the hot press method and the cryogenic cold fit method is quite large, and the cold fit method is about 5 times or more higher than the hot press method.

Also, even with acetabular sockets made using the same cold fit method, the fit strength differs depending on the shape of the ``flange'' where it fits.
As shown in Figure 2, the disconnection-preventing shape of this embodiment, which sharply bites into the expanded HDP, is more effective than simply fitting with a planar protrusion due to the dimensional difference in the expanded HDP. This is effective in terms of strength, and the HDP plastic body of the acetabular socket of this embodiment will never fall off from the outer frame during use.

〔Effect of the invention〕

The present invention has the following effects. In other words, 1. Loosening at the interface between the outer frame and the HDP plastic body is less likely to occur when loads are repeatedly applied in daily life, and uneven wear due to this is less likely to occur. 2. The fit strength of the outer frame is increased. It is not necessary to create a large number of through holes to improve the shape of the acetabular socket, and the acetabular socket can be formed without losing the rigidity of the outer frame.

3. Also, since there are no through holes or recesses on the top surface where the load and strain are greatest during daily life, it is possible to obtain higher reliability in terms of strength and abrasion resistance than conventional products.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the acetabular socket manufactured in this example, Fig. 2 is a cross-sectional view of the 1-IDP plastic body, Fig. 3 (A) is a cross-sectional view of the outer frame body, (b) is (b)
Figure 4 is a cross-sectional view of the acetabular socket, Figure 5 is an enlarged view of the main parts of
The figure is a sectional view of the conventional example, and Figure 6 is an enlarged view of 22 in Figure 5.
FIG. 7 is a comparative explanatory diagram of the fitting strength of this embodiment and the conventional example.

Claims (1)

[Claims] In the acetabular socket, which consists of an outer frame that is fixed to the hip bone with cement or the like, and a plastic body that holds a slidable femoral ball in the socket, the plastic body is molded with ultra-high molecular weight polyethylene and then heated with liquid nitrogen. Then, a plurality of protrusions are arranged on the inner peripheral surface of the outer frame made of titanium, stainless steel, or ceramics, and the cooled and shrunk plastic body is press-fitted into the outer frame at room temperature. Method of manufacturing acetabular socket.