Abstract
Introduction
Total leg muscle function in hip OA patients is not well studied. We used a test-retest protocol to evaluate the reproducibility of single- and multi-joint peak muscle torque and rapid torque development in a group of 40–65 yr old hip patients. Both peak torque and torque development are outcome measures associated with functional performance during activities of daily living.
Material and Methods
Patients: Twenty patients (age 55.5±3.3, BMI 27.6±4.8) who underwent total hip arthroplasty participated in this study. Reliability: We used the intra-class correlation (ICC) and within subject coefficients of variation (CVws) to evaluate reliability. Agreement: Relative Bland-Altman 95% limits of agreements (LOA) and smallest detectable difference (SDD) were calculated and used for evaluation of measurement accuracy. Parameters: Maximal muscle strength (peak torque, Nm) and rate of torque development (Nm•sec-1) for affected (AF) and non-affected (NA) side were measured during unilateral knee extension-flexion (seated), hip extension-flexion, and hip adduction-abduction (standing), respectively. Contractile RTD100, 200, peak was derived as the average slope of the torque-time curve (torque/time) at 0–100, 0–200 and 0 peak relative to onset of contraction. Protocol: After 5 min level walking at self-selected and maximum speeds each muscle group was tested using 1–2 sub-maximal contraction efforts followed by 3 maximal contractions 4s duration. Statistics: The variance components were estimated using STATA12, with muscle function and occasion as independent variable and patients as random factor, using the restricted maximum likelihood method (=0.05).
Results
For all exercises and sides, the ICC's for peak torque were good (0.81–0.96) with CVws ranging from 5.0–10.8%. Similar good ICC's were observed for RTD200 on the non-affected side (0.83–0.93), whereas most exercises (4/6) on the affected side showed moderate to good ICC (0.72–0.82). We found moderate CVws for RTD200 with 12.8–18.7% and 10.3–18.9%, affected and non-affected, respectively. With few exceptions the ICC's and CVws for RTD100 were moderate to poor on the affected side but good to moderate on the non-affected side. The SDD's for peak torque ranged from 14.9 Nm to 39.0 Nm, equal to relative LOA of 13.9–23.8%. For RTD200, the SDD's were 77–257 Nm•sec-1 and 29.2–86.2%, absolute and relative, respectively. With few exceptions interventions measuring RTD100 and RTDpeak would have to find changes exceeding 60% for them to be statistical significant.
Conclusions
Our novel set-up for lower limb isometric muscle testing showed overall good reproducibility for peak torque, moderate for RTD200, while poor for RTD100 and RTDpeak. The results for peak torque and RTD200 are promising for defining relevant changes in muscle function in future longitudinal clinical trials in this patient group.
