Characterizing Shank Angular Velocity During Gait in Individuals Post-ACLr Using IMUs in Ecological Settings

Abstract

Individuals post ACL reconstruction (ACLr) exhibit decreased knee extensor moments during gait in the absence of visible gait deviations that can last up to 2 years post-surgery. Inertial measurement unit (IMU) derived shank angular velocities (skAV) can be used to detect knee extensor moment asymmetries during gait in individuals 3 months post-ACLr; providing a clinical tool for identification of altered mechanics. These methods could be expanded to quantify gait mechanics during daily activities if skAV asymmetry can be detected during more ecological gait tasks. PURPOSE: To compare skAV asymmetry during ecological gait in individuals 3 months post-ACLr to controls. METHODS: 7 individuals (4 F, 33 ± 9.6 yrs) 84 ± 20 days post-ACLr without observable gait deficits and 5 healthy controls (4 F, 24 ± 2.8 yrs) performed 2-5 bouts of unconstrained walking intermixed with standing and sitting. Sagittal skAV was measured using IMU tri-axial gyroscopes (128Hz) affixed to lateral shanks bilaterally. Peak negative skAV after heel strike was identified (2nd order Butterworth filter; high pass 0.25 Hz; low pass 6 Hz) using a previously validated algorithm. skAV for each limb was averaged for 20-231 continuous steps of gait per walking bout. skAV asymmetry was calculated as the ratio between surgical/non-surgical limbs (ACLr) and dominant/non-dominant limbs (control). Independent t-test was used to compare skAV ratios between groups; α ≤ .05. RESULTS: On average, skAV ratios were 0.89 ± 0.09 and 1.00 ± 0.09 for the ACLr and control groups, respectively (p = 0.024). CONCLUSIONS: Consistent with previous studies, individuals after ACLr demonstrate reduced skAV in the surgical limb during loading response as evidenced by a smaller ratio compared to controls. Differences between groups during natural gait tasks performed with other daily tasks suggest that skAV asymmetries are detectable in less controlled settings. Given the capabilities of IMUs to collect and store large amounts of data, these data support the use of IMUs for assessing the quality of gait mechanics throughout the day. Understanding the extent to which individuals adopt altered loading outside of the laboratory is needed for the development of training interventions aimed at mitigating altered gait mechanics during early rehabilitation following ACLr.