Reliability, concurrent validity and minimal detectable change of the hand-held dynamometry for the assessment of knee muscle strength in patients with revision total knee arthroplasty.

OBJECTIVE: To determine the concurrent validity, reliability, and minimal detectable change (MDC) of the hand-held dynamometry (HHD) for knee strength measurement in patients with revision total knee arthroplasty (r-TKA).

DESIGN: A reliability and validity analysis.

SETTING: Orthopedic and physical therapy services of university hospital.

PARTICIPANTS: The study included 42 patients with r-TKA.

INTERVENTIONS: Not applicable.

MAIN OUTCOME MEASURES: Knee muscle strength assessments were performed by two physiotherapists in three different sessions by using HHD. Participants were instructed to exert a maximal force for lasting five seconds against HHD. The first examiner performed the strength testing, and after 30-minutes rest, the second examiner performed the same procedure for inter-examiner reliability. One-hour later from the initial testing, the first examiner reperformed the strength testing for intra-examiner reliability. The correlations of the knee extensors and knee flexors strength with 50-foot walking test (50FWT) and 30-second chair stand test (30CST) were assessed for concurrent validity.

RESULTS: The inter-examiner reliabilities of knee extensors and flexors strength measurements were 0.97 and 0.95 respectively. The standard error of measurement (SEM) and the minimal detectable changes at 95% confidence level (MDC95 ) for knee extensors were 10.39 and 28.65 Nm, and SEM and MDC95 for knee flexors were 8.70 and 23.99 Nm, respectively. The intra-examiner reliabilities of knee extensors and flexors strength measurements were 0.96. SEM and MDC95 for knee extensors were 12.00 and 33.09 Nm, and SEM and MDC95 for knee flexors were 7.78 and 21.45 Nm, respectively. The knee muscle strength showed strong significant correlations with physical performance tests (all, p< 0.05).

CONCLUSIONS: The HHD is a reliable and valid method for assessment of static knee strength after r-TKA. The HHD can be used to quantify changes in knee strength, and also assists the clinicians to determine the effect of rehabilitation programs on muscle strength following r-TKA surgery.