Posterior tibial subluxation of the posterior cruciate-deficient knee.

Ten subjects with unilateral posterior cruciate ligament-deficient knees were studied, comparing the knee mechanics of the affected knee with the mechanics of the opposite normal knee. The static squat test was used to determine knee forces and moments through measurements made on roentgenograms. Statistically significant increases occurred in posterior translation of the tibia in all knees at high knee flexion angles, but not uniformly at low knee flexion angles. The results suggest that posterior tibial subluxation occurs in vivo during certain activities of daily living. Posterior tibial subluxation occurred in positions of knee flexion near 70 degrees, establishing a new equilibrium for the system where tibiofemoral joint compression force (approximately four times one-half body weight) remained an order of magnitude greater than tibiofemoral shear forces (approximately 10% of one-half body weight).