Biomechanical analysis of step-up and step-down tasks in knee osteoarthritis: Insights from leading and trailing limbs

Background: Stair climbing tests are pivotal when assessing physical performance in knee osteoarthritis patients, yet the biomechanical strategies that underpin poor stair climbing ability are heterogeneously reported. Single step tasks emulate a step-by-step gait pattern, an approach associated with knee pain when stair climbing. The objective of this study is to analyse the biomechanics and electromyography activity of both the leading and trailing limbs during single Step-up and Down tasks in knee osteoarthritis patients. Methods: Three-dimensional motion analysis captured biomechanical data of twenty participants with knee osteoarthritis (n = 20) and twenty four (n = 24) age matched controls completing isolated Step-Up and Step-Down tasks. Data was collected from both the leading and trailing limbs and analysed continuously using One-dimensional Statistical Parametric Mapping (alpha = 0.05). Findings: During Step-Up, knee osteoarthritis participants demonstrated kinematic (p < 0.001), kinetic (p = 0.045), and electromyography (p < 0.001) variance compared to control participants, whilst Step-Down induced elevated external knee adduction moments (p = 0.042). Across both tasks, knee osteoarthritis participants stood with increased lower limb flexion in quiet standing and spent a proportionally elevated time in transitional double stance during Step-Up (p = 0.02). Interpretation: Our study reveals that knee osteoarthritis patients display distinctive biomechanical strategies during single Step-Up and Down tasks, that deviate depending on whether the osteoarthritic knee is leading or trailing. Single-step tasks are a safer and practical alternative to other stair climbing tests. We hope that clinicians can use these findings to guide treatments that promote less effortful step and stair ambulation in knee osteoarthritis patients with advanced disease.