Quadriceps strength thresholds may help identify individuals with knee osteoarthritis (OA) at the brink of disability, for whom small increments in strength could improve physical function, according to study data published in Arthritis Care & Research.
Researchers recruited participants with symptomatic OA from the Multicenter Osteoarthritis Study (n=834). Patient performance on the 20-m walk test and sit-to-stand test was compared with measures of quadriceps strength for the more affected knee. Patients also completed the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) to describe difficulties with certain functional tasks. Nonparametric locally weight regression scatterplot smothers (LOESS) were used to assess the relationship between quadriceps strength and functional outcomes. The participant cohort was 65.8% women with an average age of 62.9 ± 7.9 years.
Among women, LOESS plots identified the following thresholds of strength below which the strength vs function slope was steeper: walking speed (<58 Newton-meters [Nm]), chair stand time (<32 Nm), and WOMAC-reported functions of rising from a chair and getting on or off the toilet (<38 Nm). According to these models, a 20% increase in strength for women below the strength threshold would result in an estimated 1-second improvement in walking time for the 20-m walk test. In contrast, an equivalent increase for women above the strength threshold would result in a 0.23-second faster walking time. These results indicate that women below these strength thresholds may benefit more significantly from strengthening interventions than those with greater strength. Compared with women, men had a wider range of strength values, and LOESS analyses did not identify any thresholds below which strength was more strongly related with functional outcome. LOESS plots for men suggested a relatively linear relationship between quadriceps strength and functional task performance.
Data generalizability is limited by the cross-sectional study design; future research is needed to validate the observed relationship between strength thresholds and functional outcomes. Still, these results may be useful for clinicians in identifying the patients for whom strengthening interventions may be most effective.
Bacon KL, Segal NA, Øiestad BE, et al. Thresholds in the relationship of quadriceps strength with functional limitations in women with knee osteoarthritis [published online August 29, 2018]. Arthritis Care Res. doi:10.1002/acr.23740