The condition of the contralateral knee may induce different degrees of knee extensor strength asymmetry and affect functionality in individuals with unilateral or bilateral osteoarthritis

Loss of knee extensor strength in individuals with knee osteoarthritis (KOA) may induce inter-limb strength asymmetries and alter functionality. The aims were to analyse whether the condition of the uninvolved knee (advanced to severe KOA or no affection) may induce different degrees of knee extensor strength asymmetry in individuals with KOA and to study whether functionality may differ in cases of unilateral or bilateral KOA.

Sixty-eight subjects with advance-to-severe KOA were categorized into two groups (unilateral or bilateral KOA). The knee extensor strength ratio (KESR), and self-reported and performance-based functionality were analysed and compared. Sex and age were independent factors. One- and two-way analysis of variance assessed for significant between-group differences (95% confidence interval (CI)).

Participants with unilateral KOA presented with 20% knee extensor strength asymmetry. The mean difference with the bilateral KOA group in terms of Knee Extensors Strength Ratio was 0.2 (95% CI 0–0.3; P = 0.021), of the Oxford Knee Scale score was 4.2 (95% CI 3.4–5.1; P = 0.037), and of the Timed Up and Go was 1.3 s (95% CI 0.5–2.2 ; P > 0.05). There were significant sex and age interactions ( P < 0.05).

Individuals with unilateral or bilateral KOA present with different degrees of knee extensor strength asymmetry. The non-affected knee seems to help to better develop functional tasks in cases of unilateral condition. The findings may help the design of tailored strengthening interventions in which each knee condition in individuals with KOA should be considered.