Characterizing Knee Loading Asymmetry In Individuals Following Anterior Cruciate Ligament Reconstruction Using Inertial Measurement Units

Abstract

Clinically it is expected that gait mechanics will be restored by 3 months post ACL reconstruction (ACLr), however, biomechanical studies suggests that reduced knee extensor moments persist well after 3 months. Extensor moment asymmetries are often present in the absence of observable knee flexion deficits making them difficult to detect clinically. Inertial measurement units (IMU) are able to detect gait spatiotemporal asymmetries, but it is not known if variables measured with IMUs are related to knee moment asymmetry during gait. PURPOSE: To determine the relationship between knee extensor moment asymmetry and IMU-measured sagittal plane shank angular velocity asymmetry during gait in individuals 3 months post-ACLr. METHODS: 8 subjects (6 females, 23.9 ± 12.4 yrs) performed 4 walking trials 98.4 ± 12.7 days post-ACLr. Sagittal shank angular velocity (128Hz) was measured with tri-axial gyroscopes within IMUs attached to the anterior lower leg bilaterally. Knee extensor moments were quantified using motion analysis (kinematics, 250Hz; ground reaction force, 1500Hz). Stance phase and loading response were determined using previously established algorithms. Peak shank angular velocity (skAV) and knee extensor moment (kEXT) were identified during loading response. skAV and kEXT asymmetry were calculated as the ratio between involved and uninvolved limbs. Pearson’s product correlations were used to determine the relationship between skAV and kEXT; significance α ≤ .05. RESULTS: On average, skAV and kEXT ratios were 0.90 ± 0.11 and 0.77 ± 0.35 at 3 months, respectively. skAV and kEXT ratios were positively correlated at 3 months (r= .822;p=.012). CONCLUSIONS: skAV is part of the functional heel rocker, the mechanism associated with tibial progression during loading response phase of gait. These data suggest that individuals 3 months post-ACLr utilized different heel rocker mechanics, resulting in decreased skAV in the involved limb. skAV asymmetries are correlated with knee extensor moment asymmetry, however, there is not enough to support a causal effect at this time. The strong correlations between skAV and kEXT ratios suggest that IMUs can provide important information regarding knee loading deficits in individuals following ACLr. A larger sample size is needed to determine the clinical feasibility of IMU use for detection loading asymmetries.