Hip Abductor Strength Reliability and Association With Physical Function After Unilateral Total Knee Arthroplasty: A Cross-Sectional Study

Abstract

Because people with total knee arthroplasty (TKA) have persistent functional limitations and disability, identifying modifiable risk factors for persistent disability is warranted. Before surgery, people have pervasive lower extremity muscle weakness. The fact that hip abductor muscle strength is often not targeted in postoperative rehabilitation may contribute to functional limitations. Study objectives were: (1) to examine the reliability of handheld dynamometry (HHD) for measuring hip abductor strength and (2) to determine whether hip abductor strength contributes to physical function beyond the contribution of quadriceps muscle strength. This was a cross-sectional study. Two-hundred ten participants underwent quadriceps and hip abductor muscle strength testing and measurement of physical function (performance-based and self-reported outcomes). Correlation and regression equations were built to determine the relationships of strength, pain, and functional ability. A subset of 16 participants underwent hip abductor strength testing at 2 sessions to determine the reliability of the measure. Measuring hip abductor strength with HHD yielded excellent relative reliability, with an intraclass correlation coefficient (ICC [2,3]) of .95 and a 95% confidence interval of .86 to .98, but moderate absolute reliability, with a minimal detectable change (with 95% confidence) of 47.6 N and a 95% confidence interval of 35.5 to 76.5. Hip abductor strength made a significant additional contribution to performance-based measures of physical function after anthropometric covariates and quadriceps muscle strength were accounted for. Hip abductor strength did not show bivariate correlations with patient-reported measures of physical function and did not contribute to patient-reported physical function after covariates and quadriceps muscle strength were accounted for. A cause-and-effect relationship between hip abductor strength and physical function could not be established. In people with unilateral TKA, HHD testing of hip abductor strength is reliable. Hip abductor strength contributes to performance-based but not patient-reported measures of physical function in people with unilateral TKA.