The objective assessment of biomechanical asymmetries during movement tasks is used to monitor rehabilitation following anterior cruciate ligament reconstruction (ACLR). Marker placement is an important source of methodological variability within human motion analysis. It is currently unclear how marker placement error effects the interpretation of biomechanical asymmetries throughout post ACLR rehabilitation. The aim of this investigation was to determine the effect of random marker placement variation on the interpretation of inter-limb differences during a change of direction (CoD) task. Forty-seven participants 9 months post-ACLR and fifty uninjured controls completed a 90° CoD task on both limbs. Inter-limb differences in kinematic and kinetic metrics during the CoD stance phase were calculated for both groups using the Vicon Plug-in Gait model, and ACLR subjects were classified as having ‘normal’ or ‘abnormal’ inter-limb differences relative to the control group. Simulated random marker displacements based on published marker placement error ranges were then repeatedly applied to the lateral thigh, femoral epicondyle and tibia markers. ACLR inter-limb differences were recalculated each time, allowing the estimation of 95% confidence intervals and minimal identifiable between-session changes. ACLR subjects were also reclassified relative to the control group after each simulation and the percentage of participants to change classification was calculated. Marker displacements caused large deviations in inter-limb difference measures in several variables including hip rotation angle, knee abduction angle and knee abduction moment, thus limiting the ability to identify participants with large inter-limb differences relative to a control group. These findings highlight the challenges in using marker-based biomechanical models to conduct objective assessments of inter-limb differences during CoD tasks.

运动任务期间生物力学不对称性的客观评估用于监测前交叉韧带重建（ACLR）后的康复情况。标记放置是人体运动分析中方法变异性的重要来源。目前尚不清楚标记放置错误如何在整个ACLR康复后影响生物力学不对称的解释。这项研究的目的是确定方向改变（CoD）任务期间随机标记位置变化对肢间差异的解释的影响。ACLR后9个月有47名参与者和50名未受伤的对照者完成了两肢90°CoD任务。使用Vicon插入式步态模型计算两组CoD站立阶段运动学和运动学指标的跨际差异，并将ACLR受试者分类为相对于对照组具有“正常”或“异常”跨肢差异组。然后将基于已发布的标记放置误差范围的模拟随机标记位移重复应用于大腿外侧，股骨上con和胫骨标记。每次都会重新计算ACLR肢间差异，从而可以估算95％的置信区间和最小的可识别会话间变化。每次模拟后，ACLR受试者也相对于对照组进行了重新分类，并计算了改变分类的参与者百分比。标记位移导致在多个变量（包括髋旋转角度，膝盖外展角度和膝盖外展力矩）的两肢间差异测量值中产生较大偏差，因此相对于对照组，限制了识别两肢间差异较大的参与者的能力。这些发现凸显了在CoD任务中使用基于标记的生物力学模型对肢间差异进行客观评估时所面临的挑战。