Effect of Arm Support as a Compensatory Mechanism on Knee Joint Kinetics During Sit-to-Stand in Patients with Osteoarthritis

Sit-to-stand and stand-to-sit transitions are biomechanically demanding tasks commonly impaired in individuals with knee osteoarthritis (QOA). While upper limb support is frequently used to facilitate task execution, its impact on three-dimensional knee joint loading patterns remains underexplored. This study aimed to examine the influence of arm-assisted (aSTS) versus unassisted (uSTS) executions on knee joint kinetics in individuals with end-stage KOA. Eighteen patients performed three repetitions of both aSTS and uSTS tasks. Kinematic and kinetic data were collected using a 3D optoelectronic motion capture system and force platforms. Knee flexion/extension (KFM), abduction/adduction (KAM), and internal/external rotation (KRM) moments were calculated through inverse dynamics. Differences between tasks were assessed using Statistical Parametric Mapping (SPM), and the Total Joint Moment (TJM) and its components were analyzed across three movement phases: ascending, standing, and descending. SPM revealed significant reductions in KFM during the ascending and descending phases in uSTS compared to aSTS. Although KFM remained the primary contributor to the TJM across all phases and conditions, the uSTS execution was associated with a slight increase in the relative contributions of KAM and KRM, suggesting a compensatory redistribution of joint loading. These findings highlight the role of upper limb support in modulating interplanar knee joint kinetics during STS transitions and underscore the importance of evaluating multi-planar compensatory strategies in individuals with KOA.