Tibiofemoral contact mechanics with a femoral resurfacing prosthesis and a non-functional meniscus.

BACKGROUND Increased contact stress with a femoral resurfacing prosthesis implanted in the medial femoral condyle and a non-functional meniscus is of concern for potential deleterious effects on tibiofemoral contact mechanics. METHODS Peak contact pressures were determined in seven fresh frozen human cadaveric specimens using a pressure sensitive sensor placed in the medial compartment above the menisci. A knee simulator was used to test each knee in static stance positions (5 degrees/15 degrees/30 degrees/45 degrees) and through 10 dynamic knee flexion cycles (5-45 degrees) with single body weight ground reaction force which was adjusted to the living body weight of the cadaver donor. All specimens were tested in three different conditions: untreated knee (A); flush implantation of a 20mm resurfacing prosthesis (HemiCAP) in the weight bearing area of the medial femoral condyle (B); complete radial tear at the posterior horn of the medial meniscus with the femoral resurfacing device in place (C). FINDINGS On average, flush device implantation resulted in no statistically significant differences when compared to the untreated normal knee. The meniscal tear resulted in a significant increase of the mean maximum peak contact pressures by 63%, 57%, and 57% (all P< or =0.05) at 15 degrees , 30 degrees and 45 degrees static stance positions and 78% (P< or =0.05) through the dynamic knee flexion cycle. No significant different maximum peak contact pressures were observed at 5 degrees stance position. INTERPRETATION Although the condition of a meniscal tear without the resurfacing device could not be compared, possible effects of reduced meniscal tissue and biomechanical integrity of the meniscus must be considered in an in vivo application.