Handgrip and contralateral knee flexion strength as key predictors of daily physical activity in severe knee osteoarthritis.

Purpose: In this study, factors associated with physical activity in patients with end-stage knee osteoarthritis were investigated using a high-precision wearable monitor. It was hypothesised that affected-side knee muscle strength would significantly relate to objectively measured activity. Methods: A total of 58 patients with end-stage knee osteoarthritis scheduled for total knee arthroplasty were recruited, between September 2024 and April 2025, and evaluated. Evaluations included handgrip strength, skeletal muscle index, and isokinetic knee extension and flexion strength. Daily physical activity was monitored for 1 month using a wearable device, which recorded the average time spent at different metabolic equivalent (MET) levels. Activity intensity was recorded in 0.1-MET increments from 1.0 MET and categorised as 1.0-1.9, 2.0-2.9, 3.0-3.9, 4.0-4.9, 5.0-5.9, 6.0-6.9, 7.0-7.9 and ≥8.0 METs. Correlations were assessed by Spearman's rank coefficient; stepwise regression was performed adjusting for age, sex and body mass index. Results: The median duration of moderate-to-vigorous physical activity ( ≥3.0 METs) was 38.8 min/day. Using bivariate correlation analysis, handgrip strength and both affected- and contralateral-side knee flexion and extension strength were significantly associated with the daily duration of activities at 4.0-4.9 METs (ρ = 0.397, p = 0.002; ρ = 0.276, p = 0.035; ρ = 0.364, p = 0.004; ρ = 0.302, p = 0.021; ρ = 0.368, p = 0.004, respectively). In contrast, skeletal muscle index was not significantly correlated with activity at any intensity level. Using stepwise multiple regression analysis, handgrip strength was a significant predictor of activities at 3.0-3.9 METs (p = 0.023), while contralateral knee flexion strength was a significant predictor at 4.0-4.9 METs (p = 0.003). Conclusion: In severe knee osteoarthritis, handgrip strength may screen patients at risk of reduced activity, while contralateral knee flexion strengthening in preoperative rehabilitation could help optimise management strategies. Level of Evidence: Level Ⅲ.