Paige E. Lin

Characterizing knee loading asymmetry in individuals following anterior cruciate ligament reconstruction using inertial sensors

Limitations in the ability to identify knee extensor loading deficits during gait in individuals following anterior cruciate ligament reconstruction (ACLr) may underlie their persistence. A recent study suggested that shank angular velocity, directly output from inertial sensors, differed during gait between individuals post-ACLr and controls. However, it is not clear if this kinematic variable relates to knee moments calculated using joint kinematics and ground reaction forces. Heel rocker mechanics during loading response of gait, characterized by rapid shank rotation, require knee extensor control. Measures of shank angular velocity may be reflective of knee moments. This study investigated the relationship between shank angular velocity and knee extensor moment during gait in individuals (n=19) 96.7±16.8days post-ACLr. Gait was assessed concurrently using inertial sensors and a marker-based motion system with force platforms. Peak shank angular velocity and knee extensor moment were strongly correlated (r=0.75, p<0.001) and between limb ratios of angular velocity predicted between limb ratios of extensor moment (r(2)=0.57, p<0.001) in the absence of between limb differences in spatiotemporal gait parameters. The strength of these relationships indicate that shank kinematic data offer meaningful information regarding knee loading and provide a potential alternative to full motion analysis systems for identification of altered knee loading following ACLr.

Compensatory Strategies That Reduce Knee Extensor Demand During a Bilateral Squat Change From 3 to 5 Months Following Anterior Cruciate Ligament Reconstruction

• BACKGROUND: Decreased extensor moments in the surgical knee during bilateral squats can persist beyond 1 year following anterior cruciate ligament reconstruction (ACLR). This is accomplished using interlimb and intralimb compensations. • OBJECTIVES: This study sought to assess loading during squatting longitudinally, 3 and 5 months post ACLR, and to determine the extent to which interlimb and intralimb compensations contribute to reduced knee extensor moments. • METHODS: In this controlled, longitudinal laboratory study, 11 individuals (4 male) underwent 3‐D motion analysis of a squat at 3 and 5 months post ACLR. A repeated‐measures multivariate analysis of variance (limb by time) assessed differences in peak knee and hip flexion angles, knee extensor moment, vertical ground reaction force, and hip‐to‐knee extensor moment ratio. Stepwise linear regression analysis was used to determine the contribution of interlimb (between‐limb vertical ground reaction force ratio) and intralimb (within‐surgical‐limb hip‐to‐knee moment ratio) compensations to the between‐limb knee extensor moment ratio. • RESULTS: A significant effect of limb was observed for knee flexion angle, knee extensor moment, vertical ground reaction force, and hip‐to‐knee extensor moment ratio, while a significant effect of time was observed for knee extensor moment and hip‐to‐knee extensor moment ratio. At 3 months, the vertical ground reaction force ratio and hip‐to‐knee extensor moment ratio predicted the knee extensor moment ratio (R2 = 0.854, P<.001). At 5 months, the hip‐to‐knee extensor moment ratio predicted the knee extensor moment ratio (R2 = 0.584, P = .006). • CONCLUSION: Individuals used interlimb and intralimb compensations to reduce the knee extensor moment of the surgical limb at 3 months post ACLR. Similar reductions in the knee extensor moment at 5 months were accomplished with only intralimb compensations. • KEY WORDS: anterior cruciate ligament reconstruction, interlimb compensation, intralimb compensation, knee extensor moment deficit, rehabilitation

Contributors to knee loading deficits during gait in individuals following anterior cruciate ligament reconstruction

BACKGROUND Altered gait mechanics following anterior cruciate ligament reconstruction (ACLr) are commonly reported in the surgical limb 2-3 months post-surgery when normalization of gait is expected clinically. Specifically, deficits in knee extensor moment during loading response of gait are found to persist long-term; however, the mechanisms by which individuals reduce sagittal plane knee loading during gait are not well understood. RESEARCH QUESTION This study investigated between limb asymmetries in knee flexion range of motion, shank angular velocity, and ground reaction forces to determine the strongest predictor of knee extensor moment asymmetries during gait. METHODS Thirty individuals 108 ± 17 days post-ACLr performed walking gait at a self-selected speed and peak knee extensor moment, peak vertical and posterior ground reaction force, and peak anterior shank angular velocity were identified during loading response. Paired t-tests compared limbs; Pearsons correlations determined associations between variables in surgical and non-surgical limbs; and stepwise linear regression determined the best predictor of knee extensor moment asymmetries during gait. RESULTS Reduced vertical and posterior ground reaction forces and shank angular velocity were strongly associated with reduced knee extensor moment in both limbs (r = 0.499-0.917, p < 0.005). Less knee flexion range of motion was associated with reduced knee moment in the surgical limb (r = 0.358, p < 0.05). Additionally, asymmetries in posterior ground reaction force and knee flexion range of motion predicted asymmetries in knee extensor moment (R2 = 0.473, p < 0.001). SIGNIFICANCE Modulation of kinetics and kinematics contribute to decreases in knee extensor moments during gait and provide direction for targeted interventions to restore gait mechanics.