IE43194B1 - A patellar prosthesis - Google Patents

Description

This invention relates generally to a patellar prosthesis for use in a knee joint - particularly a human knee joint. heretofore, various prostheses have been proposed for use in treating defective knee joints. Bousquet (U.S. Pat. Ko. 5,696,446) and Moritz (U.S. Pat. No. 5,69^-,821) disclose total knee prostheses in which the joint between the femur and tibia is completely replaced. Link (U.S. Pat. No. 5,715,765) discloses a partial knee prosthesis in which only the articulating surfaces between the femur and tibia are replaced.

The known prior prostheses for use with knee joints have been disadvantageous in that they have neglected the importance of the patello-femoral joint. By simply replacing the articulatihg surfaces between the femur and tibia as taught by link or by replacin'·, the complete joint between the femur and tibia ss taught by Bousquet and Moritz, without concern with the patello-femoral joint, one overlooks the pain and restricted motion in an arsa not necessarily affected by such replacements.

The present invention seeks to overcome the problems amd disadvantages in prior knee joint prostheses by the provision of a prosthesis to.jreplace a defective articulating surface of the patella in a patello-femoral joint.

Accordingly, this invention provides a patellar prosthesis for a patello-femoral joint, which prosthesis has an articulating surface including a ridge upstanding therefrom and is provided with means for attaching said prosthesis to the surface of the patella adjacent the patellar facet of the femur so that when the prosthesis is anchored to the patella the articulating surface - 2 43194 replaces the natural articulating surface of the patella and the ridge engages wi* an longate indentation on the patellar facet of the femur.

The function of the ridge upstanding from the articulating surface of the prosthesis is to engage an elongate indentation in the patellarfacet of the femur in the joint, so as to maintain the prosthesis and the femur in alignment with each other and discourage dislocation, whilst at.the same time allowing pain-free and unrestricted flexion of the joint. It is beneficial if the ridge upstanding from the articulating surface of the prosthesis is made somewhat larger than the corresponding ridge found in a healthy patella.

It is n feature of the present invention that the patellar prosthesis does not compromise the patellar ligamentation, and can be anchored to the patella with very little bone removal required.

The means for anchoring the prosthesis to the patella preferably comprises one or more pegs upstanding from the pro::thesis rearwardly of the articulating surface of the prosthesis. One or more grooves are advantageously formed in and around each peg. bis anchoring means nay also comprise one or more cavities in ; rearwardly directed surface of the prosthesis opposed to the articulating surface, and/or one or more but preferably two channels formed in the said rearwardly directed surface in and around the or each peg. The cavities and/or channels are preferably undercut, thereby effectively increasing the ability of the cavities cr channels to assist the anchorage of the prosthesis 319 4 to the patella.

The patellar prosthesis of the present invention may he , used in the patella-femoral joint in conjunction with a healthy femur. However, it often happens that the articulating surfaces of both the femur and the patella in the joint are defective, in which case they must both he replaced. In that event, it is most advantageous to employ the patellar prosthesis of the invention in conjunction with the· femoral prosthesis described and claimed in our Patent Specification No. 43193 out of which this Application has been divided. Also, the patellar prosthesis of the invention may be used in the knee together with a tibio-femoral prosthesis, thus creating a true total knee joint prosthesis.

A preferred embodiment of the patellar prosthesis of the present invention will now be described by way of illustration only, reference being made to the following drawings, in whieh:4- 43194 Fig. 1 is a top plan view of a fenoral prosthesis of the aforesaid patent. * Fig. 2 is a side elevational view of the femoral prosthesis of Fig. 1.

Fig. 5 is a side elevational view of a patellar prosthesis of the present invention.

Fig. 4 is an end elevational view of the patellar prosthesis of Fig. 5.

Fig. 5 is a bottom plan view of the patellar prosthesis of Fig. 3· Fig. 6 is a sectional view of the patellar prosthesis as taken on line VI-VI of Fig. 5· Fig. 7 is a partial sectional view of the patellar prosrhes-s as taken on line VII-VII of Fig. 5· Fig. 8 is a sectional view of the femoral prosthesis as taken on line VIII-VIII of Fig. 1.

Fig. 9 is a side elevational view of a patello-fsnoral joint, the articulating surfaces of which have been replaced by a patellar prosthesis of the present invention and a fenoral prosthesis of the aforesaid patent. The joint is shown in an. nr·**! ever position with the outline of the leg in phantom lines.

Fig. 10 is a. side elevational view of the patello-fencral joint of Fig. 95 but in a flex ed position.

The patellar prosthesis 15 of the present invention is for use in replacing the articulating surface of the patella in a human patello-femoral joint 11.

The patellar prosthesis 15 is anchored to the surface 43 of the patella 45 adjacent the patellar facet 17 of the fenur IS. - 5 4Ξ1Θ4 The patellar prosthesis 15 has an articulating surface 47 for engagement with the articulating surface of the femur 19 « allowing the femur and the patellar prosthesis 15 to move relative to one another. The articulating surface 47 of the patellar prosthesis 15 has a crest-like ridge 4-9 Tor engagement with the treugh-like indentation in the articulating surface of the natural femur, thus causing the femur and patellar prosthesis 15 to remain ih alignment as they'move relative to one another. The crest-like ridge 4-9 of the patellar prosthesis 15 is higher or more pronounced than that normally found on the articulating surface of a healthy patella. This is to discourage and prevent dislocation of the joint. The sides 51 of the crest-like ridge of the patellar prosthesis 15 are curved concavely in a direction normal to the ridge for engagement with the convex sides of the indentation in the patellar facet of the natural femur. The patellar prosthesis 15 has anchoring means for fixedly anchoring the patellar prosthesis 15 to the surface 4-3 of the patella 45 adjacent the patellar facet 17 of the femur 19 with the aid of bone cement. The anchoring means comprises a plurality of pegs 57 upstanding rearwardly of the articulating surface 47 for extending into corresponding cavities 59 provided in the patella 45- The anchoring means further comprises a plurality of cavities 61 and a plurality of circular channels 63 around each of the pet s 57, which cavities and channels are formed in the surface of she patellar prosthesis that faces the patella when the prosthesis is in position for allowing the bone cement to extend into the patellar prosthesis 15. More specifically the anchoring moans comprises two spaced-apart cavities 61, and two spaced- 6 43194 apart channels 6.3 around each of the pegs 57· A plurality of grooves 65 are provided in and around each peg 57 for increasing the fixation thereof. Eaeh cavity 61 is provided with undercut portions 67 for increasing their fixation, and each channel 63 also has an undercut portion 69.

The femoral prosthesis 13 of the aforesaid patent is preferably used in conjunction with the patellar prosthesis of the present invention when the articulating surfaces of both the femur and the patella are damaged.

The prosthesis 13 is for attachment to the patellar facet 17 of the femur 19, and has an elongate articulating surface 21 having a first end 23 and a second end 25. The first end 23 is elongated. A trough-like indentation 27 is provided in the articulating surface 21 of the femoral prosthesis 13 extending alO'g the longitudinal axis of said prosthesis from the first end 23 to the second end 25. The trough-like indentation 27 is de»; il· and more pronounced than that normally found in the patellar facet of a healthy femur. This indentation 27 engages with the higher than normal ridge 49 on the articulating surface of the patellar prosthesis 15 to prevent any possible dislocation of the patellar and femoral prosthesis 13, 15 as they move relative to one.another. It should be noted that the elongated first end 23 of the femoral prosthesis 13 allows the femoral and patellar prosthesis 13, 15 to be moved substantially relative to one another as the knee is reflexed and still remain in mutual engagement. The floor 29 of the trough-like indentation 27 rf the femoral prosthesis 13 is convex as it extends from the fir; ‘ end 23 to the second end 25. Likewise, the walls 31 of the - 7 194 trough-like indentation 27 of the femoral prosthesis 15 are convex transversely from the floor 29 of the trough-like , indentation 27 to the top 53 thereof. The femoral prosthesis 13 is provided with anchoring means for fixedly anchoring the femoral prosthesis 13 to the patellar facet of the femur with the aid of a typical hone cement well known to those skilled in the art. The anchoring means comprise a plurality of pegs 55 upstanding rearwardly of the articulating surface 21 for extending into corresponding cavities 37 provided in the patellar facet 17 of the femur 19« A plurality of grooves 39 are provided in and around each peg 35 for increasing the fixation thereof. Kore specifically, the anchoring means comprises two pegs 35 adjacent the second end 25 Of the articulating surface 21 and one peg 35 adjacent the first end 23 of the articulating surface. Each of the pegs 35 is slightly tapered towards the distal end to provide a wedged tapered fit into the bone cement. In addition, the femoral prosthesis 13 has flanges hl projecting rearwardly of the articulating surface 21 along portions of the sides thereof for containing the bone cement beneath the femoral prosthesis 13 to increase its fixation to the femur 19.

The femoral prosthesis 13 of the aforesaid.patent is a one-piece construction composed of a metallic material, which is preferably stainless steel or a chromium cobalt alloy. The patellar prosthesis 15 of the present invention is a one-piece construction preferably composed of a plastics material - most advantageously an ultia-high molecular weight polyethylene.

It should be noted that each peg 57 of the patellarprosthesis 15 is provided with a marker 71 of stainless steel or chromium Ί cobalt marker wire, or the like, to provide an accurate reference for radiographic determination of position and wear rates 0¾ the patellarprosthesis 15. The size of the femoral prosthesis 15 and patellar prosthesis 15 may be varied to accommodate anatomical variations encountered. However, the applicant has determined that one size of femoral prosthesis 15 and three sizes of patellar prosthesis 15 of the invention (i.e., small, medium and large) will accommodate the majority of anatomical variations encountered.

To replace the articulating surfaces of the patello-femoral 10 joint 11 with the femoral prosthesis 15 and the patellar prosthesis 15, an incision is first made to allow access to the patella 45 and the patellar facet 17 of the femur 19 by means and methods well known to those skilled in the art. The patella 45 is then retracted to expose the patellar facet 1? of the femur 19. The pat· liar facet 17 is then contoured by well known means to properly accommodate the femoral prosthesis 15. Next, the patella 45 is further retracted so that its surface 45 is exposed. Λ portion of the surface 43 of the patella 45 is removed so that the patella 45 can properly accommodate the patellar prosthesis 2015. The femoral prosthesis 15 is then fixedly anchored to the patellar facet 17 of the femur 19 with the aid of bone cement. Likewise the patellar prosthesis 15 is fixedly anchored to the surface 45 of the patella 45 with the aid of bone cement. The incision is then closed in the manner well known to those skilled in the art.

Claims (13)

1. What we claim is:1. A patellar prosthesis for a patello-femoral joint, which, prosthesis has an articulating surface including a ridge upstanding therefrom and is provided with means for attaching said prosthesis to the surface of the patella adjacent the patellar facet of the femur so that when the prosthesis is anchored to the patella the articulating surface replaces the natural articulating surface of the patella and the ridge engages with an elongate indentation on the patellar facet of the femur.

2. A patellar prosthesis as claimed in claim 1, in which the sides of the ridge are curved concavely in a direction normal to the ridge.

3. A patellar prosthesis as claimed in claim 1 or claim 2, in which the means for attaching the patellar prosSiesis to the patella comprises one or more pegs upstanding from the prosthesis rearwardly of the articulating surface of the prosthesis.

4. A patellar prosthesis as claimed in claim 3, in which there are one or more grooves formed in and around each peg.

5. A patellar prosthesis as claimed in claim 4, in which there are two pegs, each having two grooves formed therein and therearound.

6. A patellar prosthesis as claimed in any of claims 3 to 5, in which the attachment means also comprises one or more cavities in a rearwardly directed surface of the prosthesis opposed to the articulating surface.

7. A patellar prosthesis as claimed in claim δ, in which there are tv/o cavities in the prosthesis.

8. A patellar prosthesis as claimed in any of claims 3 to 7, in - 10 43194 *& f which the attachment means also comprises one or mors circular channels in the prosthesis around the or each peg. ’

9. A patellar prosthesis as claimed in claim 8, in which there are two circular channels around the or each peg. 5

10. Λ patellar prosthesis means as claimed in any of claims 6 to 9, j.n which the cavities and/or channels are undercut

11. A patellar prosthesis as claimed in any of the preceding claims and composed of a plastics material.

12. A patellar prosthesis as claimed in claim 11, in which 10 the plastics material is an ultra-high molecular ’weight polyethylene.

13. · Λ patellar prosthesis as claimed in claim 1, substantially an described herein with refer·· neo to figures > to 7«