Abstract

Background: Accurate measurement of quadriceps muscle strength is important for patients with knee osteoarthritis (OA) to evaluate intervention outcomes. As the prevalence of OA increases, due to aging of the population, understanding the time-dependent effects of aging-related decreases in muscle strength becomes necessary. This study evaluated the errors in measurement of knee flexion and extension strength using hand-held dynamometer (HHD) in individuals with knee joint OA, and to determine the minimal detectable change (MDC) over a 3-month follow-up.

Methods: This was a longitudinal, observational study of 52 individuals with knee OA treated on an outpatient basis, for whom the HHD measurements were obtained at baseline, and at the end of a 3-month follow-up. The time-dependent changes in muscle strength measurements were evaluated using a paired t-test for changes in strength between the two time points. A Bland-Altman analysis was used to identify systematic bias on strength measures. We calculated the intra-rater reliability using the intraclass correlation coefficient (ICC), and the MDC₉₅.

Results: There were no differences in HHD measurements for knee extensors and flexors between the two time points. There was no evidence of fixed or proportional bias. The intra-rater reliability was high, with an ICC (1,1) ≥ 0.85. The MDC₉₅ was 0.23 Nm/kg for knee extension and 0.17 Nm/kg for knee flexion.

Conclusion: HHD measurements can have good reliability for standardized strength testing methods, used in clinical practice. The MDC₉₅ values can be used to monitor change in knee strength over time and the efficacy of interventions.