CA1074053A

CA1074053A - Ceramic prosthetic device

Info

Publication number: CA1074053A
Application number: CA258,611A
Authority: CA
Inventors: Martin Salzer; Helmut Locke
Original assignee: Ceramtec GmbH
Current assignee: Ceramtec GmbH
Priority date: 1975-08-09
Filing date: 1976-08-06
Publication date: 1980-03-25
Also published as: SE405800B; SE7513305L

Abstract

ABSTRACT OF THE DISCLOSURE
An implant for an endoprosthesis for human or veterinary use, and for mounting on the end of a femur. A spherical surfaced cap member with a frusto conical surfaced central opening fits over the neck of a femur and includes a thrust plate received in the femur for transmitting thrust forces from the femur to the cap member. The frusto conical surface may be grooved and include recesses and projections for improving bonding with the femur and the thrust plate may have mechanical retaining means for the cap or be screw fastened to the femur.

Description

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The invention relates to an implant for an improved endoprosthesis, which is compatible with the structural requirements and conditions of the skeleton and which results in a strong connection between the prosthesis and the bone immediately after the surgical insertion operation, without the use of bone cement, and using wear and corrosion-resistant materials which are also toxically unobjectionable. Such a spherical cap prosthesis may be used, either as part of a complete prosthesis - for which an acetabulum is also necessary - or the spherical cap may be used as a partial prosthesis - in which case, the external diameter of the ball is made larger and engages in the natural acetabulum.
An artificial join~ replacement of sintered oxide ceramic for these and similar fields of application has already been described in German Offenlegungsschrift DT-OS 2 318 459. A joint head on a worked femur head, or a joint roller, is there described which is in engagement with the artific-ial ~oint socket and which also consists of sintered high melting point metallic oxides. This structure, however, leads to a number of difficulties in practice. Under actual conditions, the femur head can only poorly be worked into a prismatic polygon. The resulting wide tolerances arising then do not permit a close fit of the implant. Moreover, there is a danger of bone fracture in the region of the neck of the femur as a result of the unspecific loading, since considerable torques occur when the implant is screwed on with the aid of the self-tapping thread.
It is furthermore apparent from a report by F. Betzel: "Kunststoffe in der plastischen Chirurgie der Gelenke" (Plastics in plastic surgery of the joints) in "Melsunger medizinisch-pharmazeutische Mitteilungen", Issue 100 (1963), pages 2478 - 86, that endoprostheses were introduced by the Judet brothers with the first clinical applications in 1948. In particular, the report describes types made of metal and plastic, and also plastic hip surgery , with Pyrex-Bakelite* caps by Smith-Peterson. Through pain caused by loading or stress and by movement, the occurrence of infections, material damage and, in some cases, also because of degenerative shrinkage of the head and neck stump of the bone, it was necessary that * both Pyrex and Bakelite are trade marks - la -- : .
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these plastic surgery caps be removed at an early stage. Such a cap cannot be expected to remain on the bone stump for a lengthy period as the cap fits only loosely.
In German Utility Model DT-GM 75 09 026, an attempt to eliminate the foregoing disadvantages by uniting this floating mounting of the cap closely and securely with the joint head with as little bone cement as possible is described. The cap consists of metal in which surface unevenness is provided on the inside with an opening to the outside.
Cap-shaped composite endoprostheses of metal and plastic are shown in Swiss Patent Specification 560,538 and German Patent Specification DT-PS
876 739. Here the artificial joint head is spherical or mushroom-shaped and the anchoring stem or shank mounted on the underside may simply be straight or curved.
Although these implants permit careful treatment of the bone and also do not particularly aggravate bleeding conditions during the surgery, they have not yet been successful in practice because the metal and plastics materials employed do not result in long-anticipated life of the implanted endoprosthesis. Experience with ceramic implants has shown that design improvements have by no means yet been exhausted. In fact,in use of these artificial joint replacement parts, various disadvantages have become manifest which can be traced back to design of the hip joint pros~hesis.
Thus, the problem which the inventors confronted was to provide a one- or multi-part implant for an improved endoprosthesis which comp~ies with the structural conditions of the skeleton in an improved manner which also results in a strong connection between the prosthesis and the bone immediately after the surgical operation without employing bone cement while employing wear and corrosion-resistant materials which are also non-toxic.
An improvement towards simplified manufacture of the implant was also required. And with the new implant, resection of the bone is minimal resulting in decreased surgical operative intervention.
This problem is met in making the central opening of the spherical cap of conical form and mounting over the conically worked femur head and

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femur neck as an exact fit. A thrust plate transfers the forces between the femur head and the neck of the femur.
More particularly in accordance with the invention there is provided, an implant for an endoprosthesis for mounting on the prepared neck of a femur which comprises a spherical surfaced cap member, the cap including a frusto conical central opening therein defining an inside surface for mounting over the neck of the femur, and a thrust plate for engaging the inside surface of said opening and received in the femur for transferring thrust forces from said femur to said cap.
In the spherical cap member the central opening may have circular or spiral grooves.
In a variation of the spherical cap, the internal cone of the central opening may have axial recesses.
The inner surface of the spherical cap may also have axial pro-jections.
The thrust plate may have a projection as a supplementary mechanical retaining means. The thrust plate may advantageously be provided with a threaded hole in the longitudinal direction for the purpose of effecting supplementary fixing to the bone by means of a screw.
An oxide ceramic, preferably highly pure aluminium oxide, may be employed for the spherical cap and also for the thrust plate.
A description of specific embodiments of the invention now follows with reference to the accompanying drawings in which;
Figure 1 is a central longitudinal section through a femur with a novel prosthesis mounted thereon;
Figures 2, 3 and 4, respectively, show sections along lines II-II, III-III, and IV-IV, of Figure l;
Figures 5 and 6 show plan views of the embodiment of the two respective thrust plates with alternatively arranged projections.
As can be seen in Pigure 1, a ceramic implant consists of a spherical cap 1 with an optionally insertable thrust plate 4 which is secured in turn to the prepared femur 10 by means of a draw screw 13. In preparing the . . . : .. . ,,, . , : . .:. . . . . . . , - .

~ ~ 7 ~ .. ;b ,, 1 damaged femur 10, the natural spherical shape of the femur head 2 is altered to a cylindrical shape with a key-hole type saw capable oE curved cutting.
This working or dressing is effected in a plurality of stages. The process is begun using a larger key-hole type saw and in so doing, it is determined whether the cylindrical stub is located centrally with respect to the neck of the femur, if necessary, any off-centre is rectified with a smaller key-hole type saw. The cylindrical stub is then formed into a cone with a special tool3 the cone ratio being between 1:10 and 1:6. This ratio is defined as the difference between the dlameters of the cone at two perpendi-cularly separated cross-sections divided by the perpendicular distance of separation of such two sections. Next the height of the cone is determined with a suitable gauge and any projecting edge is cut away. To increase further the hold which the spherical cap 1 later to be attached, will hav~
on the conically worked femur head 2, a thrust plate 4 is inserted in the bone lO. The free spaces for the thrust plate 4 and also for the draw screw 13 are made with a drill and chisel.
To secure the implant on the prepared femur, the thrust plate 4 is first placed in the free space and the cap 1 is pushed over it. The cap 1 having a notching frusto conical surface is then forced on to the conical bone stump together with the thrust plate 4. The implant is now seated in closely conforming manner on the conical bone stump and, by means of the thrust plate 4, can also be further secured by means of a surgical screw 13 which can be introduced into the threaded hole 11 and tightened.
A washer 14 may be employed between the head 13' of screw 13 and the bone 10.
In Figures 2 and 3, the circular recesses 6 and the axial recesses 7 for effecting the securing of the prosthesis to the bone can be seen. Both forms of possible surface contouring in the inner part of the spherical cap 1 permit durable anchoring of the implant to the bone by the natural bone tissue growth and the adhesion of the tissue concerned being promoted by these recesses and projections 8. The projections 8 serve at the same time for the primary fixing of the implant and secure it against rotary movement. Figure 4 shows the threaded hole 15 in which screw 13 is received.
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1 Figures 5 and 6 show alternative arrangements for projections 9 and 9' on two respective thrust plates 4 and 4'.
The upper part of each thrust plate 4 is of flattened tapered form, whereas the lower part is more elliptical. Grooves 11 (see also Fig. 4) assist in durable anchoring of the implant part by invasion or ingrowth of bone substance, just as in the case of the recesses 6 and 7. The projections 9 and 9' are directed so that the back of the thrust plate 4 or 4' is applied in closely conforming relation to the circular profile of the bone stump and engages in a corresponding recess in the spherical cap 1. The effect of the projections 9 or 9' is to prevent the cap 1 being pulled off the prepared femur head 2. The projection 9' is rotated through 90 with respect to - projection 9, but the function of the two is similar.
In order to obtain a friction and wear-resistant implant, the surface of the spherical cap 1 is polished.
An advantage of the cap-shaped form of construction for the ceramic implant is that biocompatible materials may be used and cement-free implantations can be provided which is particularly advantageous for young patients and results in a hip joint prosthesis which is both durable and stable. By using the spherical ceramic cap, surgical operative measures can be minimi~ed and firm seating of the implant can be ensured by working the bone to fit accurately. Due to the conical shaping between the implant and the bone, an improvement in the mechanical force flow is obtai~ed. In practice, it is found that loading of the implant is possible immediately after the operative procedures, 90 that the length of stay in hospital can be considerably shortened. The closely conforming or mating shape of the implant, as well as the working of the hip joint bone associated therewith, result in an optimum pressure to the femur, enable bone tissue damage to be minimized or eliminated. In comparison with all stem or shank protheses, only a minimum stiffening of the femur will occur with this cap prosthesis.
Although the cap prosthesis described finds most use in human implantation, it is also suitable for veterinary purposes.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An implant for an endoprosthesis for mounting on the prepared neck of a femur which comprises a spherical surfaced cap member, the cap including a frusto conical central opening therein defining an inside surface for mounting over the neck of the femur, and a thrust plate for engaging the inside surface of said opening and received in the femur for transferring thrust forces from said femur to said cap.

2. An implant as defined in claim 1, the surface of the central opening having circular or spiral grooves therein.

3. An implant as defined in claim 1, the frusto conical surface of the central opening including axial recesses.

4. An implant as defined in claim 1, the frusto conical surface of the central opening including axial projections.

5. An implant as defined in claim 1, the thrust plate including a projection as supplementary mechanical retaining means for said cap member.

6. An implant as defined in claim 5, a longitudinal threaded hole defined in the thrust plate, for receipt of a screw threaded member for retaining said thrust plate with respect to said femur.

7. An implant as defined in claim 1, 5 or 6, the cap member and thrust plate consisting of an oxide ceramic.

8. An implant as defined in claim 1, the thrust plate including a projection as a supplementary mechanical retaining means for said cap member, the surface of the central opening including arcuate grooves, axial recesses and axial projections and the cap member and thrust plate consisting of highly pure aluminium oxide.