Effects of position and speed on joint torques and knee shear after ACL injury

Purpose: The purpose of this study was to assess the effect of joint positi on and movement speed on hip (HT) and knee (KT) extensor torque, HT/KT rati o (HKR), and anterior tibial shear (S) in presurgical-ACL deficient (PRE; N = 15), post-ACL reconstructed (POST: N = 15), and uninjured controls (CON; N = 15). Methods: Measurements were recorded on a semirecumbent variable r esistance, closed-chain dynamometer. Tests were conducted at 1 and 1.5 Mz a nd maximum speed at 33% and 50% IRM. HT, KT, and S were recorded during the extension phase of the cycle (85 degrees -25 degrees of knee flexion). Res ults: KT was greatest when the knee was more flexed, whereas HT dominated w hen it was more extended. This suggests that the hamstrings, as a component of the hip extensors. may generate considerable propulsive force during kn ee extension, which may help counter anterior tibial shear. S increased whe reas KT decreased, suggesting that the quadriceps continue to generate shea r force despite the decreasing mechanical advantage producing KT. Increasin g knee extension speed significantly decreased S in the POST and CON groups . The correlations between KT and S changed from significantly negative to significantly positive as the knee extended from 85 degrees to 25 degrees i n the POST and CON groups. This may be related to the orientation of the pa tellar tendon, relative to the tibial longitudinal axis that shifts from a posterior to anterior direction, as the knee extends. Conclusions: Joint po sition and movement speeds affect the magnitude of hip and knee torques and anterior tibial shear. Reducing the magnitude of S during heavy lends may be a normal phenomenon, and POST surgical subjects may retain or regain thi s function by 1 yr after surgery.