Summary

Hamstrings moment in terminal stance is important to improve gait asymmetry after ACL reconstruction.

Abstract

Introduction

Anterior cruciate ligament (ACL) injury is one of the most devastating knee injuries for young athletes. Gait asymmetry is observed even in patients who have completed an adequate rehabilitation program after ACL reconstruction. An abnormal kinematics pattern leads to an increased risk of knee osteoarthritis. For example, stiffening strategy and pivot shift avoidance gait have been reported as gait modifications of anterior cruciate ligament disease (ACLD). Therefore, biomechanical asymmetry should be analyzed between pre-and post-operation in patients with ACL injury. We hypothesized that gait asymmetry would be improved postoperatively. The purpose of the present study was to investigate the asymmetry of gait biomechanics pre- and post-ACL reconstruction.

Methods

A total of 16 ACL injured subjects (8 females and 8 males, mean age = 29.2 ± 8.3 yrs, mean body mass index = 22.6 ± 2.2 kg/m2) participated in the present study. All subjects underwent ACL reconstruction by a single surgeon. Arthroscopically-assisted ACL reconstruction was performed using semitendinosus tendon. All subjects underwent the same rehabilitation protocol, partial weight-bearing exercises began 1 week after reconstruction and gradually increased to full weight bearing. Jogging was encouraged 3 months postoperatively and return to sport was permitted 8 months postoperatively. Subjects were well enough to walk pain-free at the time of gait analysis. The protocol of the present study was approved by the University Ethics Committee and written informed consent was obtained from each subject.
Gait analysis was performed at pre- and post-operative period (> 9 months). The three-dimensional motion analysis system consisted of eight cameras (120 fps; Oqus, Qualisys, Sweden), two force plates (frequency 600 Hz; AM6110, Bertec, Columbus, OH, USA), and 46 retroreflective markers (14 mm diameter). The force plate recorded ground reaction force (GRF) data at 600 Hz synchronized with the sampling rate of the camera (120 Hz). The biomechanical parameters were chosen during the stance phase defined as heel contact and toe-off. Marker tracking was performed using Qualisys Track Manager Software (version 2.7). Three-dimensional kinetic parameters were processed in Visual 3D (C-motion Company). Three-dimensional kinematic parameters were calculated using the point cluster method. For statistical analysis, biomechanical differences were compared between affected and unaffected side at pre- and post-operative period using two-tailed paired t-test. A significant difference was defined as a P value < 0.05.

Results

Gait analysis showed that knee internal rotation moment in the terminal stance was 0.13 (0.04) Nm/kg on the unaffected side and 0.08 (0.04) Nm/kg on the affected side preoperatively (P<0.05). However, at postoperative period, the difference of knee internal rotation moment was not significant. Interestingly, hamstring moment in terminal stance was -0.32 (0.09) Nm/kg on the unaffected side and -0.21 (0.13) Nm/kg on the affected side postoperatively. Hamstring moment in terminal stance was significantly smaller on the affected side compared to the unaffected side after the surgery.

DISCCUSION: Gait asymmetry continued especially in hamstring moment after the surgery even if pivot shift avoidance gait improved. As harvesting of semitendinosus tendon is necessary, postoperative rehabilitation should be focused on hamstring as well as quadriceps muscle.