Accelerometry-based comparison of functional outcomes across total and partial knee and hip arthroplasty

Aims: To evaluate objectively measured physical activity after hip and knee arthroplasty using accelerometry, by comparing bone-preserving procedures with total athorpalsties rthorpalsties and benchmarking both against non-arthritic controls. Methods: This observational study was conducted within the UK Biobank. Adults aged 40 to 69 years with total knee arthroplasty (TKA), unicompartmental knee arthroplasty (UKA), total hip arthroplasty (THA), or hip resurfacing (HR) were identified through linked hospital records and completed seven-day wrist-worn accelerometry (Axivity AX3). Outcomes included adjusted daily step count (primary), peak cadence, moderate-to-vigorous physical activity (MVPA), and Euclidean Norm Minus One (ENMO). Surgical groups were propensity score-matched to non-arthritic controls on demographics, lifestyle factors, and comorbidities. Direct comparisons between procedure types were examined using both propensity-matched analyses and complementary multivariable regression, and adjusted for demographic and clinical covariates. Subgroup analyses considered < 12 months and ≥12 months post-surgery. Results: A total of 2,283 participants were included (TKA = 860, UKA = 162, THA = 1,168, HR = 93). Compared with matched controls, TKA and THA patients showed persistently lower activity, while UKA and HR achieved levels similar to controls. In the knee cohort, UKA patients walked significantly more steps/day than TKA (9,150 vs 7,920; + 15.5%, p < 0.001) with higher cadence. In the hip cohort, HR patients outperformed THA (10,122 vs 9,139 steps/day; + 10.6%, p = 0.032) and demonstrated higher peak cadence, and HR remained comparable to controls. All groups fell within the 'somewhat active' to 'active' step-count range (7,500 to 12,499 steps/day). Conclusion: UKA and HR are associated with higher postoperative activity compared with total arthroplasty (TKA, THA). Accelerometry provides an objective, scalable assessment of functional recovery, highlighting procedure-specific differences that should be considered alongside implant longevity when selecting surgical options.