Can Data From Force Plate Technologies Identify Knee Loading Deficits During Squats Post ACLr

Despite a focus on restoring knee loading, knee extensor moment (KEM) deficits persist across rehab post-ACL reconstruction (ACLr). Reduced surgical KEM can be difficult to detect clinically because it is present without observable joint angle differences but with very subtle loading adjustments. This could contribute to its persistence. However, current commercial force plate technologies may allow for the clinical identification of KEM deficits. PURPOSE: This study investigated the diagnostic accuracy of 3 approaches to estimate KEM deficits using: 1) vertical GRF (vGRF), 2) vGRF and center of pressure (COP), and 3) GRF and 2D moment arm (MA) data compared to gold standard (GS) approach. We hypothesize that all approaches will have strong predictive ability compared to GS but vGRF only will be least effective. METHODS: Kinematic and kinetic data (3D motion capture, 2 force plates) were collected on 40 individuals (27.0 ± 10.3 years; 24 females; 113.5 ± 22.6 days post-ACLr) performing bilateral squats. Limb symmetry index (LSI, surgical/non-surgical) was calculated at peak knee flexion for all methods. GS approach used KEM calculated with inverse dynamics equations (LSI-KEMGS). LSI-GRF was calculated with vGRF. LSI-KEMCoP was calculated with vGRF and COP position using previously described methods, and LSI-KEMMA was calculated as the product of GRF and 2D sagittal plane knee MA (horizontal distance between knee axis and GRF vector). Linear regression and ICC(2,k) examined the relationship and concurrent validity between LSI-KEMGS and LSI-GRF, LSI-KEMCoP and LSI-KEMMA. Specificity and sensitivity (LSI threshold ≥0.85) determined diagnostic accuracy. RESULTS: LSI-GRF, LSI-KEMCoP, and LSI-KEMMA predicted LSI-KEMGS (R2 = .56, p < .001; R2 = .74, p < .001; R2 = .85, p < .001, respectively). ICC(2,k) values were .49 (95% CI [-.22, .80]), .92 (95% CI [.85, .96]), and .96 (95% CI [.92, .98]), with sensitivity of .72, .94, 1, and specificity of 1, .5, 1. CONCLUSION: Vertical GRF data only is not adequate to detect KEM deficits. The inclusion of COP position and 2D MA data strengthened the predictive ability and resulted in superior diagnostic accuracy. These data can be derived from force plates and synchronized 2D video technologies and may be valuable detection of KEM deficits that are not clearly observable post-ACLr.