DE7910636U1 - Femoral head cap for endoprosthesis - Google Patents

Description

Applicant: Feldmühle Aktiengesellschaft, Fritz-Vomfelde-Platz 4, 4ooo Düsseldorf 11

Annex to the entry from April 9, 1979
Pat / 12.747 / vB-Hx

Femoral head cap for endoprosthesis.

The invention relates to a femoral head cap for endoprostheses which is essentially spherical in shape and has a recess for partially receiving the femur. The use of spherical caps at the proximal end of the femur is known from a large number of references and, for example, in GB-PS 72o o92; 764 6oo,
U.S. Patent 3,521,302; 3 925 824

DE-OS 27 24 04o; 25 12 4o7; 25 35 649; 24 22 617, DE-PS 11 64 ol9: 923 383

described. The entire state of the art has one thing in common, that a complete processing of the femoral head must be done. This processing mostly removes the supply vessels of the femoral neck largely destroyed, i.e. the supply of the bone stump is no longer guaranteed, which means necrosis of the stump occurs and, as a result, loosening of the spherical cap occurs. Another big one The difficulty with the previous fixings of the spherical caps was preventing the rotation. It has already been suggested making vertical ribs or grooves in the spherical cavity - GB-PS 72 oo 92; U.S. Patent 3,925,824 - or the attachment by fastening pins to make the same time US-PS 3,521,3o2, DE-PS 11 64 ol9, DE-PS 923 383 -

Fastening with bone cement is provided for additional caps. However, the tissue is severely damaged by the heat load that occurs during curing. There are also toxic phenomena possible through the monomer of the bone cement.

The object of the present invention is therefore to create an articular surface replacement for the proximal end of the femur, the only a minimal resection is required, in the event of failure all possible retreats, such as arthrodesis or conventional Total endoprosthesis to be left open, which also applies to complete preservation of the femoral neck only changes the tribological, but not the biomechanical conditions, furthermore a good vascular supply guaranteed, a firm primary fixation without bone cement, as well as the ingrowth of Allows bone structures for additional long-term anchoring and is easy to implant.

This task is solved by a femoral head cap as an endoprosthesis, which has a substantially spherical shape and has a recess for partially receiving the femur, with the characterizing feature that the recess in the femoral head cap is open to the neck of the femur. The femoral head cap thus, as seen in the side view, has the shape of a bathing cap, the face present in the bathing cap exposed opening faces the femoral neck. The important vessels that supply the stump are not damaged as a result. The supply of the bone is thus maintained. Only a minimal resection is required. So that is at any time a follow-up operation is possible, in which, for example, conventional endoprostheses can be used.

According to a particularly preferred embodiment of the invention, the recess of the femoral head cap is towards the femoral neck open cylinder or, according to a further preferred embodiment, an open truncated cone. The opening of the recess preferably has a smaller clear width than the largest width of the recess itself.

Due to the design of the recess as a cylinder or truncated cone, thus as a rotationally symmetrical body, results a considerable simplification in the processing of the Feinurendes. By making a centering hole in the femoral head, resection of the femoral head is possible using an oscillating saw. This allows for much tighter tolerances be respected. Furthermore, the processing of the areas in the rear of the operating area is simplified Femoral head. Because the opening of the recess has a smaller inside width than the largest width of the recess itself the cylinder stump is encompassed by more than 180 degrees by the femoral head cap, i.e. the femoral head cap is firmly anchored is and cannot tip over. The security against rotation of the femoral head cap is ensured by the non-milled stops of the Ensured femoral head, on which the ends of the opening of the recess rest.

According to a preferred embodiment of the invention, the central axis of the recess runs essentially parallel to the Femoral central axis. This arrangement of the femoral head cap is the introduction of force into the joint surface replacement is more favorable, so that the cap can be used without additional fixation means, i.e. in particular without bone cement, can be anchored in a rotationally stable and absolutely tip-over-safe manner.

A preferred embodiment of the invention provides that the femoral head cap is connected to the femur by means of a press fit. The press fit fixation provides excellent primary fixation without the need for bone cement. An essential prerequisite for the installation of a femoral head cap, however, is that tight tolerances between the femoral head and Recess of the femoral head cap are observed. Only, If the exact compliance with the tolerances is guaranteed, the insertion of a femoral head cap by means of a press fit is possible,

- 6 -

This means that the prerequisite for this is the mechanical processing of the femoral head, i.e. the resection by means of a precisely guided Tool takes place. Has been particularly useful for this. An oscillating hollow milling machine turned out to be, depending on Shape of the hollow burr, the resected parts have a cylindrical or conical shape, but the resection is carried out in such a way that in each In the case of the neck of the femur as well as the foot of the femoral head cap, no processing of the bone takes place in order to supply the blood vessels not to affect.

The recess of the femoral head cap is advantageously provided with grooves and / or ribs that are parallel and / or perpendicular extend to the cylinder or cone center axis. These grooves or ribs provide what is required for secondary anchoring Space, i.e. the place in which the bone structures can grow, in order to firmly anchor the femoral head cap respectively. Because of the loads that occur, it is advisable to use these grooves or ribs only in the side areas and not to be arranged in the forehead area of the femoral head cap because the greater load occurs in the forehead area and thereby a weakening of the femoral head cap must be avoided in this area.

It is particularly useful to provide the entire recess with a rough surface. This rough surface can already be introduced into the femoral head cap during the machining process of the recess. However, it is also possible to do it through to provide for a subsequent introduction of a further layer, this introduction possibly by flame or plasma spraying can be done. The rough surface in the area of the sides of the femoral head cap is particularly important because it is just like the ribs or grooves offer a good possibility for the bone to grow in. A weakening of the end face occurs not on. The surface of the recess is advantageous provided with pores, the size of which is more than 80 μπ \

amounts to. Experience has shown that pores have a size of less than 60 μm there is no longer any hold for the ingrowing bone. Pores with a size of less than 80 μΐη only have a slight attachment. An effective real attachment occurs preferably only from a pore size of 100 μm.

Virtually all biocompatible materials can be used as the material for the femoral head cap Materials are used. However, care must be taken to ensure that when working with the Do not cause the pan to rub off. Combinations of metal femoral head cap with polyethylene socket are possible, as well as Carbon, cobalt-based alloys, as well as special steels and titanium have proven themselves. Due to the extremely low abrasion values, which are practically close to zero and because of their excellent body compatibility, however, oxide ceramics are preferred.

According to a very useful embodiment of the invention, the femoral head cap therefore consists of high-purity sintered oxide ceramic. The term 'hpchrein ¹ ' means that the sintered oxide ceramic has a purity of over 95%, with the term ' ^{sintered oxide ceramic 1} , in the sense of the above, the sintered metal oxides of zirconium, titanium and, in particular, aluminum, as well as their mixtures understand are. According to a preferred embodiment of the invention, the femoral head cap consists of sintered aluminum oxide with a density equal to or greater than 3.92 g / cm ² , a porosity equal to or less than 2%, a water absorption equal to or less than 0.1%, a purity equal to or greater than 99 , 7% Al ₂ O ₃ , a Vickers hardness (P = 2M) equal to or greater than 22,000 N / mm ² , an average grain size equal to or less than Io μπι, an average flexural strength equal to or greater than 32o N / mm ² , a compressive strength equal to or greater 4,000 N / mm ² and a tensile strength equal to or greater than 160 N / mm ² .

Such a material gives the required high level of security

for an endoprosthesis for decades, especially through the combination of the high density with the low average Grain size and the high purity of the sintered aluminum oxide the excellent properties can be achieved. Under purity is to be understood that in the aluminum oxide as few foreign substances as possible should be as further constituents that lead to a glass-like intermediate or transition phases. This requirement is not contradicted by the fact that the starting powder, That is to say, certain additives are added to the aluminum oxide, for example magnesium oxide as a grain growth inhibitor can be.

Both Animal as well as cadaver tests carried out. After showing the hip joint, a Hole made through the pole of the femoral head. This hole was used to guide the centering pin of an oscillating Hollow milling machine with which the cylindrical implant site was prepared. At an angle of 9o degrees to the cylinder center axis then a ball segment is resected, the resection being carried out by a rotating end mill guided in the bore Type of countersink took place. The upper edges of the resulting bone cylinder were also with a Centering pin rounded in the instrument guided in the bore. The cap was then fitted with a press fit. Of the Corpse experiment showed that the femoral head cap was suitable for use has great advantages in human patients, since only a minimal resection was required, ensures a good vascular supply and a firm primary fixation without bone cement was achieved. After the reduction, the Function of the hip joint checked. There were no disabilities or dislocations.

The animal experiment was carried out with foxhounds, the 14 days after the operation an increasingly inconspicuous gait pattern exhibited. They recovered quickly and stayed for 2 months

later brought back to the kennel, where they can move around in the natural environment of the pack showed. After the operation, they were able to assert themselves fully in the pack, which, like the X-ray, was full of them The functionality and the problem-free healing of the inserted femoral head cap made of high-purity aluminum oxide ceramic was confirmed.

The invention is explained below with reference to the drawings:

Fig. 1 shows a proximal end of the femur with a hip cap attached,

2 shows the same proximal end of the femur with the hip cap attached, however, the femur was rotated by approx. 45 degrees,

3 shows a medial section through the resected femoral head, parallel to the femoral axis, with the femoral head attached Hip cap,

4 shows the section through the resected femoral head with attached Hip cap cut at a 9o degree angle to the femoral axis,

5 shows a resection scheme with an oscillating hollow milling cutter; Figures 6 to 9 show sections through the femoral head cap.

A drill (not shown) is used to enter the femoral head Io the borehole 4 is introduced, which is used to guide the centering pin 8 of the hollow milling cutter 6. The hollow milling cutter 6 has a Approach 7, on which an oscillating saw (not shown) engages, which moves the hollow milling cutter 6 along a circular arc 11 emotional. Analogously, by using a face milling cutter (not shown), which is also located in the borehole 4 by means of a centering pin 8 is performed, the head surface of the femoral head Io processed.

During the resection of the femoral head Io by means of the hollow milling cutter 6 At the end of the circular arc 11 there were stops 14, by means of which twisting of the femoral head cap 1 is avoided. The opening 15 the recess 16 in the femoral head cap i is directed against the femoral neck 2 of the femur 3, i.e. that the resected femoral head stump 5 both in the base region 17 of the femoral head cap 1 and

has no vascular damage in the area of the femoral neck 2. In order to avoid damaging the vessels on the femoral neck 2, the hollow milling cutter 6 is provided with a recess 9 and is rotated only by a slight oscillating movement to form the circular arc 11. After the formation of the Rounding 13, the femoral head cap 1 can be pressed on, thereby receives its final seat. On its side faces 18, it has grooves 19 into which bone material can grow. The end face 2o does not have any grooves 19 in order not to reduce the strength of the femoral head cap 1.

In FIGS. 6 to 9, there are sections through the femoral head cap 1 shown, which have conical ribs 21. The conical ribs 21 have a triangular shape. she can be pressed into the resected femoral head stump 5 by pressing will. The primary attachment is increased by these ribs, thus anchoring the femoral head cap 1 in an even more rotationally stable manner.

Claims (11)

Applicant: Feldmühle Aktiengesellschaft, Fritz-Vomfelde-Platz 4, 4ooo Düsseldorf 11 Annex to the submission dated February 23, 1982 Pat / 12.747 / vB-Hx protection claims. 1. Femoral head cap as an endoprosthesis, which is essentially Has a spherical shape and has a recess for partially receiving the femur, characterized in that that the recess (16) in the femoral head cap (1) is open to the femoral neck (2) of the femur (3). 2. Hoof cap according to claim 1, characterized in that that the recess (16) is a cylinder open to the femoral neck (2). 3. hip cap according to claim 1, characterized in that that the recess (16) is a truncated cone open to the femoral neck (2). 4. hip cap according to one of claims 1 to 3, characterized characterized in that the opening (15) of the recess (16) has a smaller internal width than that Has recess (16). 5. hip cap according to one of claims 1 to 4, characterized characterized in that the central axis of the recess (16) is substantially parallel to the femoral central axis runs. 6. femoral head cap according to one of claims 1 to 5, characterized in that the recess (16) with
Grooves (19) is provided. 7. femoral head cap according to one of claims 1 to 5, characterized in that the recess (16) with
Ribs (21) is provided. 8. femoral head cap according to one of claims 1 to 7, characterized characterized in that the recess (16) has a rough surface. 9. Hoof head cap according to one of claims 1 to 8, characterized in that the surface of the recess (16) is provided with pores, the size of which is greater
than 8o μΐη. 10. femoral head cap according to one of claims 1 to 9, characterized characterized in that the femoral head cap (1) from consists of high-purity oxide ceramics. 11. femoral head cap according to one of claims 1 to Io, characterized in that it is made of a sintered aluminum oxide with a density equal to or greater
3.92 g / cm ³ , a porosity equal to or less than 2%, a water absorption equal to or less than 0.1%,
a purity equal to or greater than 99.7% Al ₂ O ₃ ,
a Vickers hardness (P = 2M) equal to or greater
22,000 N / mm ² , equal to or equal to a mean grain size
less than Io \ xm, an average flexural strength equal to or greater than 3oo N / mm ² , a compressive strength equal to or greater than 4,000 N / mm ² , equal to a tensile strength
or greater than 16o N / mm ² . f «- ft - i ~ r - J ^ J ^ f'jf **" ! "1 'V ^ Γι ι' Ϊγ '