Test-retest reliability of maximal leg muscle power and functional performance measures in patients with severe osteoarthritis (OA)

Abstract : Purpose
To evaluate the reliability of single-joint and multi-joint maximal leg muscle power and functional performance measures in patients with severe OA.
Background
Muscle power, taking both strength and velocity into account, is a more functional measure of lower extremity muscle activity compared with the traditionally used isometric and/or isokinetic muscle strength. More functional measures are preferred to determine muscle function and as outcomes in exercise studies in patients with OA.
Methods
Subjects: 20 patients (mean age 68.7±7.2, BMI 29.0±3.9) diagnosed with severe OA and scheduled for unilateral total hip (n=9) or knee (n=11) replacement. Patients underwent a test battery on two occasions separated by approximately one week (range 7 to 11 days). Muscle power was measured using:
1. A linear encoder, unilateral lower limb isolated single-joint dynamic movement, e.g. knee flexion
2. A leg extension press, unilateral multi-joint knee and hip extension
Functional performance was measured using:
1. 20 m walk usual pace
2. 20 m walk maximal pace
3. 5 times chair stands
4. Maximal number of knee bends/30sec Pain was measured on a VAS prior to and after conducting the entire test battery.
Statistics: Within subject coefficients of variations (CVWS): measure of agreement. Intra class correlation coefficient (ICC) was calculated as single measure reliability to reflect in between patient’s variability. The calculation was based on a mixed effect model. Paired t-tests were performed to reveal systematic difference indicating a learning effect.
Results
No significant differences (deltatest-retest) were found between the leg to be operated and the contra lateral in any of the variables. Consequently, data from both legs were pooled into one group. Table 1
A systematic and significant improvement was observed for the multi-joint maximal peak power, 5 times chair stands, maximal knee bends and 20 m walk indicating a learning effect, Table 1.
For single-joint maximal peak power the observed CVws ranged from 8-26%
For multi-joint maximal peak power (leg extension) , the observed CVws was 21%
3-6. For functional performance measures, 20 m walk, 5 times chair stands, maximal number of knee bends/30sec, the CVws were 4%, 14%, and 13%, respectively.
Conclusion
Single-joint and multi-joint muscle power over the hip and knee, and functional performance measures, can be evaluated with moderate to good reliability in patients with severe OA.
The test battery is safe for elderly patients with severe OA as indicated by no increase in pain after testing (data not shown).
Familiarization sessions or a control group are most likely needed to minimize or avoid the learning effects when testing muscle function for patients with severe OA.