DE4411508A1 - Ceramic hip joint ball test appts. - Google Patents

Abstract

The ball (6) has a conical bore (13) for accepting the conical journal (8) of a prosthetic shaft, whereby the inner surface of the conical bore is subjected to hydrostatic press. A journal protrudes into the conical bore with an intermediate space (4) between the sides of the journal and the inner bore surface. The space forms a pressure chamber which is sealed in the axial direction w.r.t. the curved upper side of the ball and w.r.t. atmosphere. Bores (5,9) in the journal enable the inner chamber to be filed with a liquid. The journal also contains a vent bore which can be closed off.

Description

The invention relates to a device for testing ceramic hip joint balls according to the preamble of claim 1.

Modular hip joint balls essentially consist of a shaft part, e.g. B. made of metal or fiber-reinforced plastic, on the conically shaped At the end, a ball adjusted in the cone angle is placed. This bullet has been around Manufactured increasingly from ceramics in the mid-1970s.

The hip joint balls in modular total hip prostheses must can sustain significant mechanical loads in the long run.

However, the resilience of hip joint balls is due to the unavoidable material microscopic defects limited. To achieve the desired long life of To ensure hip joint balls have balls with defects of critical size in the Final inspection of production to be sorted out.

State-of-the-art non-destructive test methods such as B. Exam using X-rays or ultrasound, cannot be used for this task because their sensitivity is insufficient.

The is considered a suitable test method for critical defects in ceramic materials Proof test. The proof test is an overload test in which the ratio of Test load for assumed load in the application for the balls surviving the test an allowable minimum lifespan can be calculated. This proof test is described in A.G. Evans, S.M. Wiederhorn: Proof testing of ceramic materials - an analytical basis for failure prediction, International Journal of Fracture, Volume 10 (1974), Pages 379-392.

A special device for the proof test for ceramic hip joint balls is in the Report BMFT-FB-T 83-278, Federal Ministry for Research and Technology, December 1983, H.R. Maier, A. Krauth, pages 36 to 39. At  this device tension in the ball is achieved in that in the conical Hole a rubber plug is pushed in, or that one in the conical hole filled viscous liquid is pressurized. That kind of strain leads to a stress distribution in the sphere that does not correspond to that in the Use case by attaching the ball to the conical pin of the Prosthesis socket is generated. Because of this type of stress, the face of the vault opposite the face of the conical peg charged. In a valid proof test, however, the voltage distribution at the Check as closely as possible the voltage in the application. This is with the mentioned loading device is not the case, so that possibly balls be separated out, which would meet all requirements of the application. You also need a new rubber stopper for each test, as this is the Load and / or damage during removal.

Another proof test device for ceramic hip joint balls is in the report "Development of proof test concepts for ceramic hip joint ball heads", R. Schäfer, U. Soltesz, D. Siegele, IWM report T 18/89, Fraunhofer Institute for Material mechanics, December 1989, pages 10 to 15 and 44. Here will Water filled in the opening of the ball and pressurized and at the same time must a force is applied to the outer pole area of the ball. For this, a Counter bearing used, which loads the pole area. Through this counterforce be caused that the unphysiologically high exposure to water pressure in the Vault area is reduced. You also need this external force around the Press the ball onto a sealing ring that counteracts the liquid or water seals the atmosphere. By superimposing two loads one should better simulation of the voltage distributions can be achieved in the application. This however, leads to an impractical and complicated test procedure without it is ensured that the desired voltage distribution is really achieved.

The invention has for its object a based on the proof test method To improve the test device for ceramic hip joint balls so that the im Use case voltage distribution with sufficiently high accuracy and Reliability is achieved and beyond this test device Technical practice requirements for ease of use are sufficient.

This object is achieved by the characterizing feature of claim 1.  

Due to the type of loading according to the invention, the entire area of the conical bore with the desired pressure, the The decisive advantage over the known methods is that the Vault area, as in the case of use, is free of internal pressure. This is the Load during testing absolutely the same as in the application.

Contrary to a known procedure described above, the ball not be subjected to an additional force from the outside in order to achieve a To achieve an approximation of the load situation in the event of an operation. This is the Usability significantly simplified, so that automatic handling devices can be used in a simple manner.

In an advantageous embodiment, a pin protrudes into the conical bore for testing in such a way that between the side surface of the pin and the inner surface of the Bore an intermediate space is formed, which forms a pressure chamber and in the axial Extension towards the top of the vault of the hip joint ball and the Atmosphere is sealed. This creates a pressure chamber with simple means created so that only the conical side surface of the bore with Pressure is applied. For filling a pressure medium or a liquid in According to the invention, the interspace is provided with bores in the journal.

According to the invention, the space is sealed in axial extension for sealing Sealed sealing rings that rest on the pin.

Conveniently, in addition to the holes used to fill the Serve liquid, closable vent holes are arranged in the pin.

The invention is described below using an exemplary embodiment and a Drawing explained in more detail.

In the figure, an embodiment of a device according to the invention for testing ceramic hip joint balls 6 is shown. The balls 6 have a conical bore 13 , whereby a cavity open on one side is formed. At the inner slimmer end of the conical bore 13 there is a vault-like recess 7 . The ball is made of ceramic z. B. aluminum oxide ceramic or zirconium oxide ceramic.

The essential part of the test device 1 is a metallic pin 8 , which has a smaller diameter than the conical bore 13 , so that the ball 6 can be placed over it. A sealed intermediate space 4 is formed between the pin 8 and the ball 6 by two spaced-apart sealing rings 2 , 3 which are guided in grooves.

The pin 8 contains an axial bore 9 which extends into the area of the intermediate space 4 and is connected to this at this height by a further bore 5 . Liquid, preferably water, is pressed through the bores 9 , 5 into the intermediate space 4 under the desired test pressure.

For height adjustment of the ball 6 on the pin 8 , a plate 10 is provided on the pin 8 .

In order to hold the ball 6 in the defined position during the testing process, a counter bracket 11 which can be pivoted in is used. It should be emphasized that this counter bracket 11 has no load function. The shape of the counter bracket 11 can, for. B. also have the shape of an acetabular cup.

In addition to the holes 5 , 9, which are used to fill the pressure medium, a closable vent hole 14 is arranged in the pin 8 .

During the final inspection, all balls, not just random samples, become this one Subjected to testing. The pressure of the liquid to be used for this test becomes previously determined depending on the ball type. The balls that this test survive, have increased security for use.

Claims (5)

1. Device for testing ceramic hip joint balls ( 6 ) which have a conical bore ( 13 ) for receiving a conical pin of a prosthesis socket, the inner surface of the conical bore ( 13 ) being acted upon by hydrostatic pressure, characterized in that only the conical side surface of the bore ( 13 ) is pressurized. 2. Device according to claim 1, characterized in that a pin ( 8 ) protrudes into the conical bore ( 13 ) such that an intermediate space ( 4 ) is formed between the side surface of the pin ( 8 ) and the inner surface of the bore ( 13 ) , which forms a pressure chamber and which is sealed in axial extension against the top of the arch of the hip joint ball ( 6 ) and the atmosphere. 3. Apparatus according to claim 2, characterized in that bores ( 5 , 9 ) for filling a liquid into the space ( 4 ) are arranged in the pin ( 8 ). 4. Apparatus according to claim 2 or 3, characterized in that the intermediate space ( 4 ) is sealed in the axial extent via sealing rings ( 2 , 3 ) which rest on the pin ( 8 ). 5. Device according to one of claims 2 to 4, characterized in that in addition to the bores ( 5 , 9 ) a closable vent hole ( 14 ) is arranged in the pin ( 8 ).