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Objectives and questions: Deficits in lower extremity strength and postural balance are common in knee osteoarthritis (OA) and may persist after total knee arthroplasty (TKA). While TKA reliably improves pain and patient reported outcome measures (PROMs), many patients continue to experience residual functional impairments that may restrict activity participation and elevate fall risk. The magnitude of post-TKA deficits in strength and balance as well as their interrelationship are unclear.

Material and methods: Twenty-nine patients 1 year post-TKA and 32 controls were included in this study. Participants underwent balance testing (Biodex Balance System), bilateral lower extremity strength measurement (isokinetic knee flexion/extension, isometric hip abduction, normalized to body mass), and PROMs (Knee Osteoarthritis Outcome Score KOOS) were documented. The limb symmetry index (LSI) was calculated. Group differences were tested with rank-sum tests (p<0.05) and multivariate regression analysis (Ordinary least squares). The balance–strength relationship was analysed by Spearman’s rank correlation. Median and range are reported.

Results: The TKA group had a median age of 71 (52–89) years, body mass 80 (59–115) kg, BMI 26 (19–37) kg/m². The healthy group had a median age of 64 (48–80) years, body mass 78 (46–107) kg, BMI 25 (19–34) kg/m². Balance scores did not differ. Normalized knee extension (-38%), flexion (-30%), and hip abduction (-24%) strength were lower in TKA patients for both legs. In patients, extension, flexion and abduction strength were 0.99 (0.32–2.30) Nm/kg, 0.73 (0.32–1.21) Nm/kg and 0.47 (0.21–1.28) Nm/kg, respectively. For control subjects extension, flexion and abduction strength were 1.59 (1.02–2.51) Nm/kg, 1.05 (0.63–1.77) Nm/kg, 0.62 (0.32–0.92) Nm/kg, respectively. Multivariate regression confirmed strength differences after adjusting for age and body mass. Knee-related quality of life (KOOS QoL) was lower in TKAs (-25%). Post-TKA balance and strength correlated weakly for TKA (min rho=-0.28; p>0.15) and controls (min rho=-0.30; p>0.09).

Discussion and conclusions: One year post-TKA, lower extremity strength deficits persist despite comparable balance. Weak correlations suggest balance may recover independently of strength. These findings support continued, targeted strength-focused therapeutic exercise. The large variability in strength among patients indicates that quantitative lower extremity strength measurements should be performed to identify individuals who will benefit from long-term training.