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Successful medial unicompartmental knee arthroplasty is becoming standard; however, the “screw-home” mechanism, internal femoral rotation on a fixed tibia as the knee is fully extended, should be taken into account with lateral compartment arthroplasty. Twenty-nine consecutive lateral unicompartmental arthroplasties were performed with our unique tibial component positioning in 10° to 15° of internal rotation to compensate for the “screw-home” mechanism. The Hospital for Special Surgery knee score and serial radiographs were used in the evaluation of each patient. The mean duration of follow-up was 12.4 years with no revisions. The HSS score was excellent or good in all knees. The average postoperative femoral-tibial alignment was 5° of valgus, and the average posterior tibial slope was 6°. Lateral unicompartmental arthroplasty can provide excellent long-term results with modified positioning of the tibial component.

BACKGROUND: Unicompartmental knee arthroplasty has been used to treat elderly, low-demand patients, but the literature is sparse regarding the use of this procedure for younger, active patients. The purpose of the present retrospective study was to evaluate the results of unicompartmental knee arthroplasty in younger, more active patients. METHODS: Forty-one patients underwent forty-six consecutive unicompartmental knee arthroplasties with use of the Miller-Galante system between 1988 and 1996. All of the patients were sixty years of age or younger and all were physically active. The Hospital for Special Surgery knee score and the University of California at Los Angeles activity assessment were used to rate the function and to determine the activity level of each patient, respectively. Serial radiographs were used to evaluate the status of prosthetic fixation, femorotibial alignment, and the progression of arthrosis in the unreplaced compartment. Long-term survivorship was calculated with use of Kaplan-Meier analysis. RESULTS: The mean duration of follow-up was eleven years. Of the forty-five knees that were available for follow-up, three had been revised. The Hospital for Special Surgery score was excellent for thirty-nine (93%) of the remaining forty-two knees and good for three. The University of California at Los Angeles activity assessment score was 6.6 ± 1.4 for the knees in which the original prosthesis had been retained and 7.3 ± 1.5 for those in which it had been revised. Two asymptomatic patients had revision of a modular tibial component because of substantial radiographic evidence of polyethylene wear; one of these patients had exchange of the polyethylene insert and the tibial tray, and the other had exchange of the polyethylene insert only. A third patient underwent revision total knee arthroplasty because of continuing knee pain and a progressive tibial radiolucent line that was >2 mm in width. The average postoperative femorotibial alignment was 5° of valgus. Nine knees had progression of arthritis in the unresurfaced compartment; none of these knees were revised, and none of the patients had deterioration in the Hospital for Special Surgery score. Kaplan-Meier analysis demonstrated an eleven-year survivorship of 92%. CONCLUSIONS: At an average duration of follow-up of eleven years, unicompartmental knee arthroplasty was associated with pain relief and excellent function in a cohort of patients who had been sixty years of age or younger and active at the time of surgery.

Successful medial unicompartmental knee arthroplasty is becoming standard; however, the "screw-home" mechanism, internal femoral rotation on a fixed tibia as the knee is fully extended, should be taken into account with lateral compartment arthroplasty. Twenty-nine consecutive lateral unicompartmental arthroplasties were performed with our unique tibial component positioning in 10 degrees to 15 degrees of internal rotation to compensate for the "screw-home" mechanism. The Hospital for Special Surgery knee score and serial radiographs were used in the evaluation of each patient. The mean duration of follow-up was 12.4 years with no revisions. The HSS score was excellent or good in all knees. The average postoperative femoral-tibial alignment was 5 degrees of valgus, and the average posterior tibial slope was 6 degrees . Lateral unicompartmental arthroplasty can provide excellent long-term results with modified positioning of the tibial component.