The effect of stuffing the patellofemoral compartment on the outcome of total knee arthroplasty.

BACKGROUND: The effect of so-called stuffing of the patellofemoral compartment at the time of total knee arthroplasty (that is, increasing the anterior patellar displacement, the anteroposterior femoral size, or the combined anteroposterior patellofemoral size) has not been well studied. The purpose of the present study was to evaluate the effect of stuffing the patellofemoral compartment on the outcome of primary total knee arthroplasty.
METHODS: A retrospective review of 1100 primary total knee arthroplasties that had been performed in 1997 and 1998 was conducted. Eight hundred and thirty arthroplasties (75.5%) met the diagnostic and minimum two-year follow-up criteria for inclusion in this report. Radiographic measurements were made to determine preoperative and postoperative anterior patellar displacement, anteroposterior femoral size, combined anteroposterior patellofemoral size, anterior femoral offset, and posterior femoral offset. Regression analysis was performed to determine the effects of changes in these variables on the range of motion, the Knee Society Knee Score, the Knee Society Function Score, the Knee Society Pain Score, and the rate of lateral retinacular release.
RESULTS: Preoperative to postoperative changes in anterior patellar displacement, anteroposterior femoral size, combined anteroposterior patellofemoral size, anterior femoral offset, and posterior femoral offset had no clinically meaningful effect on the range of motion of the knee or on any of the Knee Society scores. Increases in anterior patellar displacement were associated with a lower probability of the need for a lateral retinacular release. Increases in measured anteroposterior femoral size were associated with a higher probability of the need for lateral release. Even when combined, however, these relationships explained only 10.1% of the observed variance in the need for lateral retinacular release. Moreover, analyses indicated that patient gender, large as opposed to medium patellar size, and absolute femoral component size influenced the likelihood of lateral release more than did anterior patellar displacement and measured anteroposterior femoral size.
CONCLUSIONS: Our findings do not support the widely held belief that stuffing of the patellofemoral joint results in adverse outcomes after total knee arthroplasty. Furthermore, the need for lateral release appears to be multifactorial and likely involves a more complex set of factors. Thus, without evidence of other identifiable causes of failure, we do not recommend revision for the treatment of pain of an overstuffed knee joint.