Individuals with anterior cruciate ligament (ACL) reconstruction are at increased risk to develop knee osteoarthritis (OA). Gait analysis including kinetics and electromyography of walking and stair use can provide insight to everyday knee joint dynamic loading. Previously, those with ACL rupture have shown altered gait patterns up to one year postsurgery.

PURPOSE:​ To compare lower extremity gait patterns of those with ACL reconstruction (>​1yr) to a control group. We hypothesized that the ACL group would have 1) reduced knee extensor strength, 2) reduced knee flexion angles, 3) reduced knee extensor moments, 4) increased hip extensor moments, 5) increased external knee varus moments, 6) reduced knee extensor activity, 7) increased knee flexor activity, 8) increased hip extensor activity, 9) increased quadriceps:​hamstring co-contraction, and 10) altered medial and lateral thigh muscle activity patterns when compared to the control group.

METHODS:​ Eighteen ACL reconstructed individuals (26 ± 6 years, 6 ± 4 years from surgery) and 18 healthy controls (26 ± 4 years) participated in this study. Participants performed three ascending and descending trials on a three step staircase and three walking trials leading with the right and left leg, respectively. Kinematic and kinetic recordings were collected using an 8-camera motion analysis system, and portable force platforms were positioned on the first and second stair steps. Reflective makers were placed on the lower extremities and trunk. Electromyography (EMG) data were collected from the vastus lateralis [VL], vastus medalis [VM], biceps femoris [BF], semimembranosus [SM], and gluteus maximus [GMax]. Using inverse dynamics, internal hip abduction moments, hip extension moments, knee extension moments, and external knee varus moments were calculated during the stance phase of walking for stair ascent and descent (two steps). Maximum moments were averaged across trials and normalized to body mass. A linear envelope (10 Hz low-pass filter) was used to determine maximum EMG values during the stance phase of each step. Maximum EMG values were averaged across three trials and normalized to the MVIC. Co-contraction ratios were determined for knee extensors and flexors (VL+VM and BF+SM) and for medial and lateral muscle activity (VM and SM, VL and BF, respectively). One-way ANOVAs were used to test for main effects of group (ACL and control) on maximum joint moments and EMG activity. Significance was set at p<​0.05.

RESULTS:​ During walking and stair use (on the second step) those with ACL reconstruction exhibited lower knee extensor moments and greater hip extensor moments compared to the control group. Hip extensor EMG activity was greater in the ACL reconstruction group during walking and stair use. Knee flexor activity was increased during walking and the first step of stair ascent. Increased medial thigh co-contraction was found in the ACL group during walking and increased knee extensor and flexor co-contractions was found during the first step of stair ascent.

CONCLUSION:​ Walking and stair ambulation highlight altered knee joint loading patterns in those with ACL reconstruction surgery. Individuals compensate for lower knee extensor moments by increasing hip extensor moments, and this was reflected in EMG data. Reduced knee extensor moments may protect the repaired ACL from excessive strain or may result from impaired neuromuscular control. Those with at least one year post-ACL reconstruction increase medial knee compression during walking.