Comparison of Dynamic Limb Valgus and Stiff Landing Between Limbs with and Without Anterior Cruciate Ligament Reconstruction

BACKGROUND: Dynamic limb valgus and stiff landing are two known risk factors for anterior cruciate ligament (ACL) injury. These biomechanical risk factors can be evaluated through motion analysis testing. HYPOTHESIS/PURPOSE: The purpose of this study was to compare risk scores for dynamic limb valgus and stiff landing between limbs with recent ACL reconstruction and uninjured (contralateral and control) limbs. METHODS: Sports motion analysis data were reviewed for 177 pediatric patients after recent primary ACL reconstruction (ACLR) and 63 uninjured control subjects ages 8-17 years. 3D motion analysis data were collected while subjects performed the following sports-related tasks: heel touch from 6” or 9” step (depending if height >155 cm), drop jump from 41 cm height, lateral shuffle, forward-backwards deceleration, single leg hop, and 45° cutting. Each limb was scored for components of dynamic limb valgus (hip stability, pelvis stability, trunk stability) and stiff landing (shock absorption, hip strategy) based on the kinematic and kinetic measures in Table 1. Each scoring category was rated for each applicable task as adequate (2), borderline (1), or inadequate (0) based on values from the literature and laboratory norms. Percentage scores by scoring category were compared among reconstructed, contralateral, and control limbs using chi-square tests and ANOVA. RESULTS: For the overall risk factors, stiff landing was worse in controls compared with both the reconstructed and contralateral limbs of patients (p<0.001), but dynamic limb valgus was worse in the ACLR limbs (p≤0.03) (Figure 1). Shock absorption (p<0.001), hip strategy (p<0.001), and trunk stability (p=0.005) differed significantly between groups. Shock absorption and hip strategy were both worse in the control group compared with the patient reconstructed and contralateral limbs, while trunk stability was best in the control group and worst in the ACLR group. CONCLUSION: Post-operative ACLR patients demonstrated better biomechanics than controls on both the reconstructed and contralateral limbs in terms of avoiding stiff landing, particularly through better shock absorption. This may reflect training in proper biomechanics during physical therapy and rehabilitation. ACLR limbs were worse than control limbs only in trunk stability, which can be corrected with targeted training and awareness. Motion analysis is useful for identifying risky movement patterns so biomechanics can be corrected prior to return to play.