Hip Abductor Strength Reliability and Association With Physical Function After Unilateral Total Knee Arthroplasty

Patients with Total Knee Arthroplasty (TKA) display persistent functional limitations and disability. Recognizing modifiable risk factors of persistent disability is warranted. Prior to surgery, patients have muscle weakness that is pervasive throughout the lower extremity. Strength of the hip abductors is often not targeted in post-operative rehabilitation and may contribute to functional limitations after surgery. The objective of this study was to investigated the reliability of hand-held dynamometry to measure hip abductor strength and to determine whether hip abductor strength would contribute physical function above and beyond the contribution of quadriceps strength. 210 subjects underwent quadriceps and hip abductor strength testing and measurement of physical function (performance-based and self-reported outcomes). Correlation and regression equations were built to determine the relationship between strength, pain and functional ability. A subset of 16 subjects underwent hip abductor strength testing at two sessions to measure reliability of the measure. Measuring hip abductor strength using HHD produced excellent relative reliability ICC2,3= 0.95 (95% CI: 0.86, 0.98) but moderate absolute reliability MDC95 of 47.6 N(95% CI: 35.5, 76.5). Hip abductor strength showed significant additional contribution to performance-based measures of physical function after accounting for anthropometric covariates and quadriceps strength. Hip abductor strength did not display bivariate correlation with patient-reported measures of physical function and did not contribute to patient-reported physical function after accounting for covariates and quadriceps strength.

It was found that in patients with unilateral TKA, testing the strength of the hip abductors using HHD is reliable. Hip abductor strength contributes to performance-based measures of physical function, but not to patient-reported measures in patients with unilateral TKA.