Linear and nonlinear measures of gait variability after anterior cruciate ligament reconstruction

The objective of this study was to assess gait variability after anterior cruciate ligament reconstruction (ACLR), as an indicative of possible altered gait pattern and a measure of recovery compared to control subjects. Forty subjects (32 male), divided into 4 groups of 10 participants, were enrolled in the study: a control group (CG), and observational groups OG-I (90 days), OG-II (180 days), and OG-III (360 days) after ACLR. All subjects underwent the same rehabilitation program for six months. For kinematic recording, each subject walked on a treadmill for 4 min at a preferred walking speed. Linear gait variability was assessed using average standard deviation (VAR) and normalized root mean square of medial-lateral (ML) trunk acceleration (RMS_ratio). Gait stability was assessed using the margin of stability (MoS) and local dynamic stability (LDS), and nonlinear variability was assessed using sample entropy (SEn). Compared to the CG, the VAR ML increased significantly in the OG-I group and decreased incrementally in OG-II and OG-III. MoS increased significantly in the OG-I group and tends to maintain in OG-II and OG-III, while LDS was greater in the CG and decreased incrementally in the OG groups. The SEn was higher in the OG groups than in the CG and increased in OG-II and OG-III. The results indicated that ACL reconstruction was followed by a progressive increase in stability and a progressive increase in variability over the postoperative rehabilitation period. In terms of stability and gait variability, six months of physiotherapy for rehabilitation after ACL reconstruction appears to be effective, but it is insufficient for a complete recovery as compared to healthy individuals.