Posterior tibial tendon dysfunction (PTTD) is a debilitating condition with multifactorial etiologies that leads to functional limitations, including biomechanical deficits in the lower limb. Previous studies have focused on gait biomechanics in patients with PTTD during walking; however, examining lower extremity biomechanics during other essential daily activities, such as step-up and step-down tasks, is crucial for understanding the functional limitations associated with PTTD.

This case-control study compared lower limb kinematics and kinetics between individuals with PTTD (n = 16) and healthy controls (n = 16) during step-up, step-down, and step-down on a medially inclined surface tasks. A 12-camera motion capture system was utilized to record three-dimensional movements of the pelvis and lower limb, while a force plate measured ground reaction forces. Hip, knee, ankle, and midfoot angles and moments were analyzed across groups using one-dimensional statistical parametric mapping. Between-group differences were consistent across tasks. Individuals with PTTD exhibited greater midfoot dorsiflexion/inversion/external rotation, ankle eversion/plantarflexion, and hip flexion angles, as well as midfoot plantarflexion/inversion moments than healthy controls. Overall, individuals with PTTD exhibited distinct movement patterns in their lower extremities compared to healthy individuals. These altered biomechanical patterns may increase stress on adjacent joints and tissues, potentially worsening the condition and heightening the risk of further injuries. These findings will contribute to the development and enhancement of rehabilitation protocols for individuals with PTTD, aiming to improve function, reduce pain, and prevent injury.