Altered 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 due to concerns about implant loading and longevity. This study provides the first three-dimensional kinematic and kinetic characterisation of high-impact tasks in high-functioning adults with total hip arthroplasty (THA), total knee arthroplasty (TKA), or unicompartmental knee arthroplasty (UKA), compared with healthy controls. High-functioning adults with a joint arthroplasty (THA=11, TKA=4, UKA=3) participated. Healthy comparison data (n=70) were obtained from prior studies adopting the same analytical framework. They completed running, 45{degrees} 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. THA had greater hip adduction angles during running 3.65{degrees} (95%CI 0.73{degrees}, 6.57{degrees}) and COD45 14.12{degrees} (95%CI 3.22{degrees}, 25.02{degrees}), compared to controls. THA participants recruited greater hip extensor moment during loading response in running, propulsion during CMJ, and in unilateral and bilateral hops, compared to controls. People with a TKA and UKA exhibited a greater internal rotation angle during running, without a concomitant increase in moments at initial contact and toe-off, compared to healthy controls. Also, TKA and UKA participants experienced reductions in knee extensor moments across all high-impact tasks, such as a 1.86 to 1.89 Nm/kg reduction during running. High-functioning individuals with a joint arthroplasty can perform demanding tasks, but often through movement strategies that may compromise long-term implant durability.