Is there a dose response for valgus unloader brace usage on knee pain, function, and muscle strength?

Objective: To examine whether there was a dose response for valgus unloader brace wear on knee pain, function, and muscle strength in participants with medial compartment knee osteoarthritis. Design: In this single-group study, participants with medial compartment knee osteoarthritis were followed for approximately 6 months. Setting: Recruitment was conducted in the general community, and testing was performed at a university laboratory. Participants: A convenience sample of patients (N=32) who were prescribed a valgus unloader brace agreed to participate, met the inclusion criteria, and completed the baseline data collection. Twenty-four participants (20 men, 4 women) completed baseline and follow-up collections. Intervention: Participants wore their valgus unloader brace as needed. Main Outcome Measures: Knee extensor, flexor, and plantar flexor strength was tested at baseline and follow-up. Participants filled out Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Medical Outcomes Study 36-Item Short-Form Health Survey questionnaires to assess pain and function. Self-selected walking velocity and stride length were objective measures of function. Brace usage (dose) and activity (step count) were recorded at least 4 days/week for the study duration. Results: Positive relationships existed between brace wear usage and percent change in step count (r=.59, P=.006) and percent change in hamstrings strength (r=.37, P=.072). At follow-up, there was significant improvement in hamstrings strength (P=.013), and trends toward improvements in WOMAC pain (P=.059) and WOMAC function (P=.089). Conclusions: Our results indicate that greater brace use may positively affect physical activity level, but there was minimal effect of brace wear dosage on lower-limb muscle strength. Only knee flexion showed a positive relationship. Our finding of no decreased muscle strength indicates that increased brace use over a 6-month period does not result in muscle impairment.