Tracking Recovery After TKA with Instrumented Timed Up and Go: Spatiotemporal, Rotational, and Strength Adaptations over Six Months

Knee osteoarthritis (KOA) is a leading cause of disability, and total knee arthroplasty (TKA) improves pain and functional mobility, although gait impairments may persist postoperatively. This study investigated longitudinal changes in patient-reported outcomes, muscle strength, and gait performance using an instrumented Timed Up and Go (iTUG) test with wearable inertial measurement units (IMUs). Twenty-two patients with end-stage KOA were assessed preoperatively and at 3, 12, and 24 weeks postoperatively. The Knee Injury and Osteoarthritis Outcome Score five-subscale composite (KOOS5) showed a significant overall change over time (p < 0.001), while isometric muscle strength showed significant overall changes across all tested muscle groups (p ≤ 0.008), with mean values demonstrating an initial postoperative decline followed by subsequent increases. Total TUG duration showed a significant overall time effect (p = 0.023), with significant reductions observed in the forward and return gait phases (p = 0.012 and p = 0.001, respectively). End-turning maximum rotational speed and sit-to-stand vertical acceleration showed significant overall time effects (p = 0.012 and p = 0.024, respectively), whereas the remaining parameters did not reach statistical significance. These findings indicate that recovery following TKA is multidimensional, with significant changes in patient-reported outcomes, muscle strength, and functional mobility. iTUG analysis identified phase-specific changes, while several turning and transitional parameters did not show significant longitudinal changes, supporting the use of targeted rehabilitation strategies focusing on dynamic stability and movement control.