DE3205527A1 - Anchoring aid for an artificial acetabulum - Google Patents

Abstract

For securing a socket implant to be fixed in a socket excavation (1) in a bone (3) a supporting element comprising a support plate section (A) and an embeddable part (B) driven into the wall of the socket excavation (1) is proposed as an anchoring means (9) between the artificial acetabulum and the bone (3). <IMAGE>

Description

description

The invention relates to an anchoring means for an artificial one Hip socket, as indicated in the preamble of claim 1.

When implanting artificial joints, for example hip joint endoprostheses, there is the fundamental problem of securing the prosthetic implant against loosening.

It is generally used to anchor the prosthesis material in or on the bone a special type of bone cement (palacos) is used. Only with ceramic prostheses a ceramic screw socket without bone cement is screwed into the socket. the However, implantation of such cementless ceramic screw sockets is limited to a few selected younger patients restricted.

When the prosthesis material is anchored by means of bone cement - as clinical experience and specialist literature show - the contact surface bond between the (metal or polyethylene) prosthesis and the cement permanently. Against it the contact surface bond between bone cement and bone is critical because through reactive remodeling processes of the bone bed after different periods of time Without exception, there is a connective tissue denarcation zone opposite the bone cement mass which initiates the loosening of the implant.

The speed of this development and the thickness of the demarcation zone is not only dependent on the nature of the bone implant bed (im yut perfused cancellous bone bed, connective tissue reaction is greater than in the less perfused, cortical bone bed), but also on the mechanical stress on the implant dependent: micro-movements of the implant cause primarily insufficient adhesion a particularly strong connective tissue reaction.

The particular problem with the acetabulum is that all Artificial cup implants (polyethylene cups) the hemispherical configuration of the Mimicking acetabular cavity, which provides security against twisting (rotation) of the hemispherical socket implant in an equally hemispherical socket bearing is problematic from the start.

This problem is explained with reference to FIGS. 1 to 3; figure 1 shows a section along a meridian of the hemispherical acetabular cavity 1 part of a pelvic bone with a firm bone cortex 2 and spongy, cancellous bone 3.

The hemispherical socket implant 4 shown in FIG. 2 is intended inserted into the acetabular cavity 1 of Figure 1 and through an intermediate cement layer that are fixed in Figure 3 (corresponding to a sectional view Figure 1) is denoted by the number 5. To secure the socket implant it has this extensions 6, knobs or depressions 7, which in the inserted state are surrounded by the cement layer 5. There are also cavities in the wall of the acetabulum Drilled holes 8 are introduced into which the cement layer 5 has also penetrated. But even these measures do not guarantee permanent protection against loosening of the implant 4.

There is an additional difficulty here in that the bone cement penetrates into the boreholes and initially pretends to be stable - but when stressed due to the lack of shear strength of the bone cement Breakage of the "pegs" of bone cement engaging in the bores 8 occur can, so that loosening is the result.

The situation is particularly critical when the load-bearing capacity of the acetabular cavity is primarily reduced, for example as a result of resorptive thinning of the socket base, in the case of the presence of rubble cysts, generally with bone decalcification as well finally in the case of a deepened (protusioacetabuli) szw. flattened pan.

As a solution to this problem, so to strengthen diluted or otherwise The following technical options have so far been available to reduce the load-bearing capacity of the acetabulum: a) flexible wire nets that are appropriately tailored and used to reinforce the bottom of the pan be placed on the bottom of the pan prior to the introduction of the cement paste b) So-called basin baskets made of flexible stainless steel, usually in a cross shape, dle be placed in the socket cavity before the cement mass is introduced.

For the versions a) and b) it is true that they are the pan bottom reinforce, but do not form a stable bond with the bone and in particular not secure against (rotation) and pulling out of the implant the cup excavation.

c) A certain protection against twisting and pulling out is only achieved with the roof shell by M. E. Müller, namely by the fact that this is a screw connection the socket roof shell of the socket implant in the socket cavity. These The pan roof shell has essentially the shape of a hemispherical space with an open bottom, with holes provided in the T-shaped wall of the basket, For holding screws that are used as fastening elements in the wall of the socket cavity let in, so be sunk.

But it has been shown that the rotation and pull-out stability of a such pan roof shell, if at all, only guaranteed for a short time is because the screws engage in a largely cancellous, non-compact bone have to. It is particularly reliable when the pan base is thinned and the bone is decalcified Screw anchoring is not possible in the first place, as experience has shown that screws are already there Turn empty when screwing into the softened bone, not to mention always threatening secondary loosening under the subsequent physiological Stress. Over time, the screws not only sit loosely in the bone, but also in the pan roof shell and can no longer serve their purpose.

A less fundamental, but practically important disadvantage is also the unwieldiness of such a pan roof shell: for example, must for the widely variable acetabular cup sizes of different coarse roof shells are kept available, and screwing in the screws increases the operating time.

The invention is based on the above-described pan roof shell, the object of the invention to provide improved anchoring means that have a larger Ensure safety by twisting and pulling out an artificial joint socket and at the same time can be easily inserted into a socket cavity.

This object is achieved by the anchoring means with the features of claim 1. Advantageous developments are in the subclaims specified.

What is decisive in the anchoring means according to the invention is that on the one hand, instead of a single-storey pan roof shell, an anchoring means is provided that is so small that several of these anchoring means in one Pfannenexkavation can be accommodated, but that on the other hand instead of the so far only loose connections between the Pfannendactschale and its countersunk parts (Screws) now a fixed connection from the outset is provided between the Support plate part and the countersink part. The countersunk part must be are there on the support plate part, where this once on the wall of a socket excavation will be on, i.e. on that area of a support plate part that is used for the Concern on a socket excavation wall is provided. The countersunk part is preferred integrally formed with the support plate part, for example by having both parts form the legs of an angle that is bent from a sheet metal strip with a flat profile is.

Preferably, however, a T-shaped anchoring means is produced made of a rustproof plate or titanium sheet, in a yelk-shaped design. Included the countersunk part is preferably in the middle of the support plate part perpendicular to this arranged standing. The support plate part is preferably curved or cylindrical also formed spherically, with the countersunk part then on the convex side of the support plate part. The latter can be designed to be bendable by hand, so that it can be adapted to the respective curvature of a cup cavity.

In another advantageous embodiment of the invention is the countersunk part is designed in the shape of a pin and riveted to the plate-shaped support part. This embodiment is particularly suitable in connection with a reinforcement unit part, which is inserted into a hole created in the socket cavity that is marked with Bone cement is filled. This creates an additional stable anchorage of the Support plate part causes without the pin penetrating into the bore exclusively made of bone cement exists and thus an increased shear stress is exposed. The reinforcement is cup-shaped and made of perforated material.

The recesses of the anchoring elements according to the invention formed by perforation are designed so that the bone cement penetrates them and through his Solidification on both sides of the recess acts like a rivet, with the cross section the recesses provided is preferably designed such that the bone cement in the non-solidified state in the case of the one exerted when inserting the anchoring means Pressure passes through the recesses and a connection after curing of the type described.

The anchoring elements according to the invention can preferably be star-shaped arrange so that an even introduction of force into the weakened pan base is guaranteed. The main thing here is the transmission of torques (Rotational stability), since the pure contact pressure without additional anchoring is transferred from the pan to the bone. For the torques to be transmitted have the T-shaped elements with a countersunk part extending in the transverse direction excellent conditions. Additional "adhesive holes" can be omitted without that loosening is to be feared.

A preferred exemplary embodiment is shown on the basis of FIGS the invention explained: Figure 4 shows in perspective an embodiment of an anchoring means.

FIG. 5 shows several anchoring means attached in a socket cavity according to Figure 4.

FIG. 6 shows a section corresponding to FIG. 3, but with anchoring means according to the invention.

FIG. 7 shows a further embodiment of the anchoring means according to the invention.

An anchoring means 9 with support plate part A and countersunk part B According to Figure 4, as Figure 5 shows, in a socket cavity 1 in the Be let in way that the support plate part on the pan base only rests on, while the vertical countersunk part is embedded in the bottom of the pan, for example is depressed. To make it easier to push in, the countersunk part B have a taper at its free end of the countersunk part.

Depending on the size of the socket, at least 3 anchors should be used 9 can be admitted. In Figure 5, for example, 3 anchoring means 9 are along arranged in an azimuthal circle of the socket cavity. To make this possible the length of the support plate part A dimensioned so small that only at least four such Lengths the length of the largest complete azimuthal circle of the cup cavity wall surpass.

After inserting the Verdnkerunysmittel 9 an additional one is not necessary Screw connection with bone screws, especially since a reliable one in the cancellous bone 3 Screw fixation is not possible anyway. A provisional security against Falling out until the cement 5 is introduced can be achieved in that the countersunk part B has a barb, for example a barb-like knob W.

After the anchoring means 9 have been inserted, bone cement is used 5 in the socket cavity 1 and applied to the anchoring means 9 and the still soft cement mass 5 according to the previously customary implantation technique, the hip socket 5 introduced.

In Figure 6, the final state is shown in section, here the Anchoring means 9 on a meridian of the hemispherical socket excavation wall are arranged.

The countersunk part B, which is embedded perpendicular to the bottom of the pan, offers a Protection against rotation. The diverging directions of the countersunk parts B ensure a simultaneous safeguard against loosening of the tension (pull-out) even after training the loosening of the bond at the bone-cement boundary, which is always to be expected for biological reasons. The support plate part A is used when the pan base is thinned and weakened this is additionally reinforced. This gain can be optimized by that the outline of the support plate part A is designed so that when placed next to each other of anchoring means 9 only small spaces remain. Several side by side anye- Arranged support plate parts A then result in an almost closed one Hemispherical surface.

To the countersunk part B the necessary for pressing into the bone To give rigidity, this countersunk part can be perpendicular to the countersink direction running cut be curved or kinked. It can also consist of a pen. Siderhakenelemente, which can be formed on the countersunk part, produce if necessary an additional holding force. However, this version is not shown in the figures reproduced.

The embodiment shown in Figure 4 is for simplicity the design and the proportions represent an optimum, because the handling is also very good is simple: The anchoring elements are distributed as regularly as possible introduced into the bone cement evenly applied in the socket cavity, whereby the countersunk parts are pressed into the bone wall. To another Layer of bone cement is then placed in the artificial socket in its target position, wherein the hardened bone cement is the connection between the individual anchoring elements and the pan is made in the manner of a supporting structure, it being necessary for stability does not depend on the connection established between bone cement and bone.

In Figure 7 is a further embodiment of the invention Anchoring means shown, the support plate part A being round, and a pen shaped countersunk part C with its jerky end attached to the support plate part by means of an end designed as a rivet 10 is. A cup-shaped reinforcement part D is adapted to the countersunk part v, which expands towards its open end. This reinforcement part also exists Made of perforated material, in which the holes form recesses through which the bone cement can pass through when it is inserted in a non-solidified state. The cup-shaped reinforcement element enables a stable connection to the bone, whereby by the protruding in the he mation part pin of the countersunk part C it is ensured that the acting shear stresses are safely absorbed and cannot function in a break, as is the case with the previous arrangements of the This could be the case, since in this case too there were no shear stresses on the bone cement work yourself.

In summary, it must be tested here that the connection between According to general clinical experience, bone cement and metal are permanently stable is. On the other hand, the bond between bone cement and Bones, which allow a certain primary adhesion, but in the long run of bones u is thickened by the development of a connective tissue demarcation zone by the principle of: mechanical protection against rotation presented here and output guaranteed even after the resorption-demarcation zone has formed. It enables thus also a permanent anchorage.

Another advantage - especially compared to the pan roof shell from MÜLLER - consists of the extremely simple one Handling which the usual surgical techniques and the operational requirements hardly noticeably enlarged.

Based on the Ausfüirungsbeispiele it has become apparent that accordingly the principle of the anchoring means according to the invention, the introduction of force from the The cup on the hip excavation does not exceed the - not with regard to its shear strength reliable - layer uus bone enzent takes place, but in particular the occurring Torque forces are introduced directly into the bone material, so that a far greater stability of the attachment can be achieved than with the previous Solutions is the case. In particular, through a radial arrangement of the countersunk parts these sicti complement each other with regard to their fastening effect, so that one Bone cement-anchoring element composite structure is created, which is a represents a stable structure for the acetabulum, which also provides a stable anchorage in the case of complete failure of the connection between bone cement and bone in the area of the pancreatic cavity secures.

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Claims (23)

Anchoring means for an artificial hip socket Anchoring means for an artificial acetabulum, with a cup cavity on the wall (1) The support plate part (A) to be attached, which is not shown that a countersunk part (B) protruding from the support plate part for insertion into the socket excavation wall is provided, which is rigidly connected to the support plate part (A) (Figures 4 to 6), and that the area of the support plate part (A) is much smaller than the wall surface of a socket cavity (1), so that only several are lined up Support plate parts (A) result in a length like the azinutai circle of the socket excavation wall is equivalent to. 2. Anchoring means according to Claim 1, that is to say e i c h n e t that the support plate part (A) can be bent by hand and by simple Tools can be shortened by cutting. 3. Anchoring means according to claim 1 or 2, d a -d u r c h g e it is not indicated that the support plate part (A) is curved cylindrically. 4. Anchoring means according to claim 3, d a d u r c h g e k e n n shows that the support plate part (A) is spherically curved. 5. Anchoring means according to claim 3 or 4, d a -d u r c h g e it is not indicated that the support plate part (A) has the countersunk part (B) on its convex side. 6. Anchoring means according to one of the preceding claims, d a it is indicated that the support plate part (A) is perforated is. 7. Anchoring means according to one of the preceding claims, d a d u r c h g e k e n n n z e i c 10 n e t that the support plate part (A) and / or countersunk part (B) is made of a plate-shaped material. 8. Anchoring means according to claim 7, d a d u r c h g e k e n n z e i c h n e t that support plate and countersink part (A and B) from one common Workpiece are made by folding. 9. Anchoring means according to one of claims 1 to 7, d a d u r c h g e k e n n n n z e i c h n e t that the countersunk part (C) is essentially a has a round cross-section. 10. Anchoring means according to claims 7 and 9, d a d u r c h it is noted that the countersunk part (C) with the plate-shaped material is riveted. 11. Anchoring means according to one of the preceding claims, d a d u r g e k e n n n z e i n e t that the countersunk part (B) with the support plate part (A) is firmly connected. 12. Anchoring means according to one of the preceding claims, d a D u r h g e k e n n n e i c h n e t that the countersunk part (B) and the support plate part (A) form the legs of an angle of at least one flat profile. 13. Anchoring means according to one of the preceding claims, d a D u r h g e k e n n n e i c h n e t that the countersunk part (B) and the support plate part (A) Form a T-profile. 14. Anchoring means according to one of claims 1 to 9, d a d u r c h g e k e n n n z e i c h n e t that the countersunk part (B) in a perpendicular to Sinking direction running cut is curved or kinked. 15. Anchoring means according to one of the preceding claims, d a d u r c h y e k e n n n z e i c h n e t that the countersunk part (B) has at least one barb (W) 16. Anchoring means according to one of the preceding claims, d a d u r g e k e n n n z e i n e t that the size of the support plate part (A) is dimensioned in such a way that only at least four lengths equal the circumference of the largest the full azimuthal circle of the cup cavity wall. 17. Anchoring means according to one of the preceding claims, d a D u r c h e k e n n n n e i n e t that the support plate part (A) is shaped in this way is that when two support plate parts are closely aligned along an azimuthal circle of the socket cavity in relation to the area of a support plate part A much smaller area remains in between. 18. Anchoring means according to one of the preceding claims, d a D u r c h e k e n n n n e i n e t that the support plate part (A) is shaped in this way is that when two support plate parts (A) are closely aligned along one Meridian of the cup cavity in relation to the area of a support plate part only a space with a much smaller area remains. 19. Anchoring means according to claim 15 or 16, d a -d u r c h y It is noted that the support plate has the shape of a partial surface of a Spherical surface is approximated, which is composed of mutually equal partial surfaces is. 20. Anchoring means according to one of the preceding claims, d a it is indicated that the countersunk part (B) is at its free end has a cutting edge (S) or point. 21. Anchoring means according to one of the preceding claims, g e k e n n z e i c h n e t d u r c h a reinforcement element (D), which the countersunk part encloses at a distance. 22. Anchoring means according to claim 21, d a d u r c h g e k e n n z e i c h n e t that the reinforcing element (D) is tapered in cross section is. 23. Anchoring means according to one of claims 21 or 22, d a d u r c h e k e n n n n z e i c h n e t that the reinforcing element (D) is cup-shaped is trained.