Lower-limb kinematics and joint moments during high-impact tasks after hip and knee arthroplasties

High-impact physical activity delivers musculoskeletal and systemic health benefits yet remains controversial for people with hip or knee arthroplasties. This study investigates the three-dimensional kinematics and kinetics of high-impact tasks in high-functioning adults with total hip arthroplasty (THA, n = 11), total knee arthroplasty (TKA, n = 4), or unicompartmental knee arthroplasty (UKA, n = 3), compared with healthy controls (n = 57) from prior studies. They completed running, 45° change of direction (COD), countermovement jumps (CMJs), and unilateral/bilateral hopping. An 8-segment biomechanical model was used to quantify 3D joint angles and internal moments. These were time-normalised and modelled using Generalized Additive Models with covariates for group, age, and task intensity. Post-hoc contrast with controls was undertaken and reported. THA participants ran with lower hip abduction angle (peak Δ6.22°), lower external rotation angle (peak Δ7.38°), and greater hip extensor moment (peak Δ1.19 Nm/kg). During jumping and hopping tasks, THA participants also showed greater hip extensor moments (peak Δ0.41-0.67 Nm/kg), compared to controls. People with TKA and UKA consistently exhibited reduced knee extensor moments across high-impact tasks. Altered transverse-plane knee mechanics were observed in TKA and UKA, characterised by lower knee external rotation angle (peak Δ8.58°-12.54°), together with reduced internal rotation moments (peak Δ0.3 Nm/kg). High-functioning individuals with hip and knee arthroplasties can perform high-impact activities, but with altered movement strategies. The long-term implications of these biomechanical adaptations for implant loading and durability remain unclear and warrant further investigation.