The Case for a Fixed-Bearing Unicompartmental Knee Arthroplasty

Douglas Naudie, M.D., FRCSC
Assistant Professor, University of Western Ontario
London, ON

First introduced in the 1970s, the unicompartmental knee arthroplasty did not gain initial widespread acceptance. Early reports by Insall and Aglietti, and Laskin suggested a high failure rate. However these studies included patients who underwent concomitant patellectomy, had inflammatory arthropathy, or who had a very thin (6 mm) tibial polyethylene component1,2. Over the subsequent decade, however, good results were reported for both medial and lateral unicompartmental designs, as the indications for unicompartmental arthroplasty gradually became better defined3,4. Longer follow-up studies have since reported ten-year survival rates without revision for unicompartmental implants ranging from 82% to 98%5-14.

In appraising the literature, however, it is important to distinguish between mobile-bearing and fixed-bearing unicompartmental implants. Mobile-bearing implants have a fully congruent articulation that moves freely on a polished tibial baseplate, and the theory of this design has been previously published15. Fixed-bearing implants have a relatively nonconforming articular surface, which can be inserted as an all-polyethylene tibial component, or as a non-modular or modular metal-backed tibial component. Proponents of mobile-bearing unicompartmental implants believe this design has improved wear characteristics over fixed-bearing implants, and thus may offer a survival advantage in the long-term16.naudiefigure_1a.jpg
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Figures 1-A and 1-B. Preoperative anteroposterior and lateral radiographs of the left and right knees of a 67-year old male patient demonstrating arthritis confined to the medial compartment of each knee.

The reality is that both designs have demonstrated excellent ten-year survivorship free of revision. Cartier and associates report a ten-year survivorship using the Marmor fixed-bearing prosthesis of 93%5. Recently, ORourke and associates report continued excellent survivorship with the same implant at a minimum of twenty-one year follow-up6. Argenson and associates report a 94% ten-year survivorship with the Miller-Galante fixed-bearing implant7. Using the same fixed-bearing implant, we report 90% ten-year survivorship; and Berger and associates report a 98% ten-year survivorship8,9.

On the mobile-bearing side, Murray and associates report ten-year survival rates free of revision of 98% using the Oxford prosthesis10. Price and associates also report an excellent ten-year (95%) survivorship with the Oxford prosthesis11. Other studies have not reproduced these numbers, however, and have actually reported lower ten-year survivorship rates than fixed-bearing implants. Keblish and Briard report 82% prosthetic survivorship at 11 years using the Oxford and Low Contact Stress (LCS) mobile-bearing implants12. Similarly, Vorlat and associates report a cumulative survival rate of 82% at ten years with the Oxford mobile-bearing implant13.

There have also been studies directly comparing the results of mobile-bearing and fixed-bearing implants. Emerson and associates showed a 99% survival for the mobile-bearing Oxford implant compared to a 93% survival for the fixed-bearing Brigham implant at 11 years16. However, an initial comparison of the Oxford unicompartmental arthroplasty implant to the fixed-bearing Marmor implant revealed a significantly higher cumulative revision rate with the Oxford implant17. Another recent study by Gleeson and associates also found that the Oxford mobile-bearing prosthesis had a higher re-operation rate and significantly less pain relief than the St. Georg sled fixed-bearing implant18.

The case for a fixed-bearing rather than a mobile-bearing unicompartmental implant, therefore, can be made on the basis of more reproducible long-term survivorship. In fact, Swedish registry data does not support the widespread use of a mobile-bearing unicompartmental implant because of the increased rates of revision observed in Sweden17,19. Fixed-bearing unicompartmental implants are probably also less technically demanding than mobile-bearing implants, which require exact balancing and intact cruciate ligaments15. Dislocation of the bearing has been described, for example, as a unique complication in association with the Oxford knee20,21.

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Figures 1-C and 1-D. Standing anteroposterior and lateral radiographs of both knees of the same patient taken ten years after bilateral medial unicompartmental arthroplasties.

A fixed-bearing implant is also more versatile than a mobile-bearing implant. A fixed-bearing implant can be successfully employed as a lateral compartment arthroplasty with excellent long-term results recently reported22. When the Oxford mobile-bearing arthroplasty is used in the lateral compartment of the knee, ten percent of the bearings dislocate21. A fixed-bearing implant also permits use of an all-polyethylene tibial component, allowing for a thicker polyethylene insert without resection of additional host bone. Excellent results using an all-polyethylene tibial component have recently been reported23. Finally, a fixed-bearing implant is less expensive than a mobile-bearing implant, particularly when an all-polyethylene tibial component is employed.

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Figures 2-A and 2-B. Standing anteroposterior and lateral radiographs of a 65-year-old female patient taken two years after lateral unicompartmental arthroplasty with an all-polyethylene tibial component.

In summary, unicompartmental knee arthroplasty remains an excellent treatment alternative for osteoarthritis confined to the medial or lateral part of the knee joint. Fixed-bearing implants have been shown to provide good pain relief and restoration of function, and have reproducibly demonstrated excellent survivorship into the second decade. This author makes the case for a fixed-bearing over a mobile-bearing implant because they are technically easier, avoid the complication of bearing dislocation, are more versatile, and less expensive.

References

1. Insall J., Aglietti P. A five to seven-year follow-up of unicondylar arthroplasty. J Bone Joint Surg Am. 1980;62(8):1329-37.

2. Laskin R.S. Unicompartmental tibiofemoral resurfacing arthroplasty. J Bone Joint Surg Am. 1978;60(2):182-5.

3. Kozinn S.C., Scott R. Unicondylar knee arthroplasty. J Bone Joint Surg Am. 1989;71(1):145-50.

4. Corpe R.S., Engh G.A. A quantitative assessment of degenerative changes acceptable in the unoperated compartments of knees undergoing unicompartmental replacement. Orthopedics. 1990;13(3):319-23.

5. Cartier P., Sanouiller J.L., Grelsamer R.P. Unicompartmental knee arthroplasty surgery. 10-year minimum follow-up period. J Arthroplasty. 1996;11(7):782-8.

6. ORourke M.R., Gardner J.J., Callaghan J.J., et al. The John Insall Award: unicompartmental knee replacement: a minimum twenty-one year follow-up study. Clin Orthop Relat Res. 2005;440:27-37.

7. Argenson J.A., Chevrol-Benkeddache Y.C., Aubaniac J. Modern unicompartmental knee arthroplasty with cement: A three to ten-year follow-up study. J Bone Joint Surg Am. 2002;84(12):2235-37.

8. Naudie D., Guerin J., Parker D.A., et al. Medial unicompartmental knee arthroplasty with the Miller-Galante prosthesis. J Bone Joint Surg Am. 2004 Sep;86-A(9):1931-5.

9. Berger R.A., Meheghini R.M., Jacobs J.J., et al. Results of unicompartmental knee arthroplasty at a minimum of ten years of follow-up. J Bone Joint Surg Am. 2005;87(5):999-1006.

10. Murray D.W., Goodfellow J.W., O'Connor J.J. The Oxford medial unicompartmental arthroplasty: a ten-year survival study. J Bone Joint Surg Br. 1998;80(6):983-9.

11. Price A.J., Waite J.C., Svard U. Long-term clinical results of the medial Oxford unicompartmental knee arthroplasty. Clin Orthop. 2005; 435:171-180.

12. Keblish P.A. and Briard J.L. Mobile-bearing unicompartmental knee arthroplasty: a 2-center study with an 11-year (mean) follow-up. J Arthroplasty. 2004; 19(7-S2):87-94.

13. Vorlat P., Putzets G., Cottenie D., et al. The Oxford unicompartmental knee prosthesis: an independent 10-year survival analysis. Knee Surg Sports Traumatol Arthrosc. 2006; 14(1): 40-5.

14. Goodfellow J., O'Connor J. The mechanics of the knee and prosthesis design. J Bone Joint Surg Br. 1978;60-B(3):358-69.

15. Price A.J., Short A., Kellett C., et al. Ten-year in vivo wear measurement of a fully congruent mobile bearing unicompartmental knee arthroplasty. J Bone Joint Surg Br. 2005;87(11):1493-7.

16. Emerson R.H., Hansborough T., Reittman R.D., et al. Comparison of a Mobile with a Fixed-Bearing Unicompartmental Knee Implant. Clin Orthop Relat Res. 2002; 404:62-70.

17. Lewold S., Goodman S., Knutson K., et al. Oxford meniscal bearing knee versus the Marmor knee in unicompartmental arthroplasty for arthrosis. A Swedish multicenter survival study. J Arthroplasty. 1995;10(6):722-31.

18. Gleeson R.E., Evans R., Ackroyd C.E., et al. Fixed or mobile bearing unicompartmental knee replacement? A comparative cohort study. Knee. 2004;11(5):379-84.

19. Robertsson O., Knutson K., Lewold S., Lidgren L. The routine of surgical management reduces failure after unicompartmental knee arthroplasty. J Bone Joint Surg Br. 2001;83(1):45-9.

20. Verhaven E., Handelberg F., Casteleyn, et al. Meniscal bearing dislocation in the Oxford knee. Acta Orthop Belg. 1991;57(4):430-2.

21. Robinson B.J., Rees J.L., Price A.J., et al. Dislocation of the bearing of the Oxford lateral unicompartmental arthroplasty. A radiological assessment. J Bone Joint Surg Br. 2002;84(5):653-7.

22. Pennington D.W., Swienckowski J.J., Lutes W.B., et al. Lateral unicompartmental knee arthroplasty: survivorship and technical considerations at an average follow-up of 12.4 years. J Arthroplasty. 2006;21(1)13-7.

23. Hyldahl H.C., Regner L., Carlsson L., et al. Does metal backing improve fixation of tibial component in unicondylar knee arthroplasty: a randomized radiostereometric analysis. J Arthroplasty. 2001;16(2):174-179.

 

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