Functional analysis of anterior cruciate ligament instability

Abstract

Eighteen males and two females (mean age, 26.5 years) underwent biomechanical assessment and Cybex eval uation prior to ACL reconstruction. Clinically, all patients had at least a 1+ grade with the Lachman, anterior drawer, and pivot shift tests, the majority being graded as 2+. Footswitch, high speed photography, force plate, and indwelling wire electrode data were collected while each subject performed free and fast walking, running, cutting, and stair climbing activities. During walking, single limb support times did not differ between the subject's involved and uninvolved limbs. Knee joint angles were similar between limbs during walking, running, and stair climbing maneuvers. Dynamic EMG tracings during walking demonstrated similar quadriceps and calf activity between limbs, while greater variation in hamstring firing was evident among subjects. During running, the involved limb had a longer duration of medial hamstring activity compared to the lateral hamstring. No significant differences were seen in either vertical or sagittal shear forces during free walking. During fast walking, higher midstance vertical forces (F2) were present in the involved limb (P < 0.05). During running, the involved limb experienced lower vertical forces (P < 0.05), while both anterior and posterior sagittal shear differences were insignificant. Straight cut maneuvers demonstrated significantly lower lateral shear and ver tical forces in the involved limb (P < 0.05). Lower lateral and sagittal shear forces in the involved limb (P < 0.01 and P < 0.05, respectively), combined with a reduced angle of the cut during the cross-cut maneuver, may be the first means to assess the functional pivot shift phenomenon ever documented. Isokinetic Cybex strength testing demonstrated a mean 14% quadriceps deficit and a mean 4% hamstring deficit in the involved limb. Achieving quadriceps and hamstring torque of 86% and 96%, respectively, was not sufficient to eliminate the subjective need for sur gical reconstruction.