Physical Fitness and Physical Activity Levels One Year After Total Hip Arthroplasty in Older Hip Osteoarthritis Patients: A Longitudinal Observational Study

Background: Total hip arthroplasty (THA) effectively alleviates pain and improves quality of life in patients with severe hip osteoarthritis (OA). However, comprehensive longitudinal data regarding physical function and objectively measured physical activity patterns following THA are limited. Objective: To establish the test-retest reliability of physical fitness measures in hip OA patients and assess longitudinal changes in physical fitness and activity following THA. Methods: Seventy-eight OA patients (mean age 73.7 ± 4.2 years, 81% women) scheduled for THA underwent comprehensive physical fitness testing and accelerometry-based physical activity monitoring. Assessments were conducted at two preoperative time points and at 4-month (n = 57) and 1-year postoperative follow-up (n = 48). The test battery included measures of muscle strength, motor fitness, and cardiorespiratory fitness. Physical activity was objectively measured using hip-worn triaxial accelerometers. Self-reported Hip disability and Osteoarthritis Outcome Score (HOOS) were collected pre- and post-operatively. Results: Good to excellent test-retest reliability was demonstrated across 23 of 24 fitness parameters. At 1-year post-op, significant improvements were observed in 23 of 45 measured parameters, including functional mobility (Timed Up and Go: -29%), walking distance (Six-Minute Walk Test: +16%), trunk endurance-strength (+71-82%), shoulder-press (+32%), various leg strength tests (+13-42%), 4m max walking-speed (+42%), moderate-to vigorous-physical activity (+63%) and daily step count, from 6004 to 7558 steps/day, (+26%). Ipsilateral-to-contralateral step height asymmetry decreased from 27% pre-operatively to 8% at 1-year follow-up. VO₂peak demonstrated a modest but significant improvement from 22.7 to 23.6 mL/kg/min (+4%) one year postoperatively. Conclusions: This study revealed low fitness and activity levels in patients with severe hip osteoarthritis before surgery, with marked improvements in physical fitness and activity measurements one year after surgery. The high reliability of the comprehensive assessment battery supports its usefulness for both research and clinical practice. These findings contribute to the existing evidence on simple, field-based fitness tests for patients with hip osteoarthritis, while also offering methodological insights and recovery trajectories.