Knee Loading Deficits During Dynamic Tasks in Individuals Following Anterior Cruciate Ligament Reconstruction

STUDY DESIGN: Controlled laboratory study, cross-sectional. BACKGROUND: Well-documented deficits in sagittal plane knee loading during dynamic tasks indicate that individuals limit the magnitude of knee loading following anterior cruciate ligament reconstruction (ACLR). It is unknown how these individuals modulate the speed of knee flexion during loading, which is particularly important as they progress to running during rehabilitation. OBJECTIVE: To investigate how individuals following ACLR perform dynamic knee loading tasks compared to healthy controls. METHODS: Two groups of recreationally active individuals participated: 15 healthy controls and 15 individuals post-ACLR (ACLR group). Participants performed 3 trials of overground running and a single-limb loading (SLL) task. Sagittal plane range of motion, peak knee extensor moment, peak knee flexion angular velocity, peak knee power absorption, and rate of knee extensor moment were calculated during deceleration. A mixed-factor multivariate analysis of variance was performed to compare differences in variables between groups (ACLR and control), limbs (within ACLR), and tasks (within control). RESULTS: Knee power absorption, knee flexion angular velocity, and rate of knee extensor moment were lower in reconstructed limbs (for the SLL task: 5.6 W/kg, 325.8 degrees/s, and 10.5 Nm/kg/s, respectively; for running: 11.8 W/kg, 421.4 degrees/s, and 38.2 Nm/kg/s, respectively) compared to nonsurgical limbs (for the SLL task: 9.7 W/kg, 432.0 degrees/s, and 19.1 Nm/kg/s, respectively; for running: 18.8 W/kg, 494.1 degrees/s, and 72.8 Nm/kg/s, respectively) during both tasks (P<.001). The magnitudes of between-limb differences in knee flexion angular velocity were similar in both tasks. CONCLUSION: Despite lower loading demands during SLL, individuals post-ACLR exhibit deficits in knee dynamics during SLL and running, suggesting an inability or reluctance to dynamically accommodate forces at the knee when progressing to running in rehabilitation.