LCS mobile-bearing total knee replacement. A 10-year's follow-up study.

INTRODUCTION: For the last three decades total knee arthroplasty surgery has been facing the renewed choice of using a traditional fixed-bearing design or a mobile-bearing system. A growing number of surgeons have elected to increase their use of mobile-bearing prostheses. We wanted to assess the reliability, in our hospital of this alternative choice.

HYPOTHESIS: Fixed-bearing and LCS mobile-bearing knees exhibit comparable long-term clinical and radiographic results.

MATERIAL AND METHODS: Between January 1994 and December 1996, 126 LCS prostheses (DEPUY) were implanted by the same operator in 101 patients (mean age was 70.0 years). The predominant underlying pathology was osteoarthritis (113 prostheses); the posterior cruciate ligament was retained in 30% of these cases which permitted a tibial tray implantation using a PCR type meniscal-bearing component; 78 prostheses were cemented; 116 prostheses included a patellar button: 46 of these resurfaced patella featured a cementless metal implant and a mobile-bearing polyethylene insert. Overall function was assessed using the SF-12 and IKS scores, and on the basis of patients' satisfaction rate. Patients' review process took place between 1st October 2006 and 1st December 2006. Of the 101 patients, 59 were alive, 39 were clinically examined and 20 completed a self-assessment questionnaire; 32 had died and 10 were lost to follow-up. The average age of the patients still alive was 78 years (79 years for those operated on for osteoarthritis, 67 years for those operated on for rheumatoid polyarthritis); Mean follow-up period at the time of this review was 11.4 years. Mean body mass index (BMI) was 30.8 kg/m(2).

RESULTS: No early infection was observed. Early complications included instability in one case, stiffness in six cases and resolutive patellar pain in three cases. Six prostheses necessitated to be revised. In the 39 reviewed patients (52 prostheses), the mean IKS knee score was 78/100, (range, 20 to 100/100), mean functional score was 66/100 (range, 0 to 100/100). Mean mobility in flexion was 105.8 degrees (range, 20 degrees to 135 degrees). The SF-12 quality of life score was assessed in 39 of the operated patients. Mean physical score was 37 (range, 22.6 to 61.2); mean mental score was 47 (range, 23.1 to 62.3). Seventeen patients were very satisfied, 18 satisfied (these combined categories representing 90% of patients), three were partially satisfied and one was unsatisfied. Forty-three radiographs were performed in 36 patients at the time of the follow-up visit: 39 of them included an A-P, a lateral and a patellar view at 30 degrees of flexion. Thirty-nine readings were normal. A radiolucent line beneath the tibial component was observed on three radiographs. An asymptomatic patellar tilt was reported in one instance. Mean tibial slope was 8 degrees (range, 1 degree to 11 degrees).

DISCUSSION: Statistical analysis of these results demonstrates a significant and long-lasting improvement in the clinical score, an early improvement (both in respect to functional score and mobility) with a late minor deterioration of the quality of this initial improvement; a poorly significant negative correlation between mobility and BMI. Despite a high satisfaction rate, it does not quite match that obtained with hip arthroplasty. No correlation was found between the observed results and patient gender, prosthesis fixation method, type of prosthesis (PCR meniscal-bearings versus rotating platform, posterior cruciate ligament retention versus sacrifice), tibial slope, limb axis, and selected patellar treatment options.

CONCLUSION: The mobile-bearing prostheses achieve results at least as good as comparable ones reported in other series; demonstrate a very low revision rate in relation to wear damages; and tolerate insufficient axis deformity corrections.

LEVEL OF EVIDENCE: Level IV. Therapeutic study.