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Greater hip abductor strength improves long-term function in knee OA
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CHICAGO — Greater hip abductor strength reduced the 5-year risk for poor functional outcomes and the 2-year risk for tibiofemoral cartilage damage worsening among certain patients with knee osteoarthritis, according to findings presented at the ACR/ARHP 2018 Annual Meeting.
The study results showed that the significant benefits of hip abductor strength were limited to patients with stronger quadricep muscles, Alison H. Chang, PT, DPT, associate professor of physical therapy and human movement sciences at Northwestern University Feinberg School of Medicine, reported. She said the findings highlight the important role of hip abductor strengthening in knee OA.
“Lower limb muscle weakness has been proposed as a factor contributing to functional decline and structural progression in patients with knee OA,” Chang said. “Previous studies have primarily focused on the role of quadriceps muscle.”
Although hip strengthening exercises have been shown to reduce pain and improve function in the short-term, Chang said it was previously unclear whether stronger hip muscles conferred additional benefits in the presence of stronger quadricep muscles.
“In theory, patients with hip weakness are likely to have concomitant quadricep muscle weakness,” Chang said. “Compared to healthy older adults, persons with knee OA have an average deficit of 20% in body weight-normalized hip abductor strength, adjusted for age and sex.”
Chang and colleagues examined the association between hip abductor strength — which was measured using a Biodex Dynamometer — with function and disability outcomes in 187 patients with knee OA, who were followed for 5 years. They also examined the relationship between hip abductor strength and cartilage damage worsening outcomes over 2 years in 165 patients with knee OA. The analyses were stratified by quadricep muscle strength.
Participants’ outcomes were assessed with MRIs and the Late-Life Function and Disability Instrument (LLFDI), which considers three function domains (total function, basic lower-extremity function and advanced lower-extremity function) and three disability domains (frequency of participation in major life tasks, limitation of ability to perform each task, and limitation to participate in instrumental home or community activities). The researchers also evaluated participants using a chair stand test. During this test, Chang and colleagues recorded the time required for participants to rise from a chair and sit down. These times were converted to a rate of completed chair stands per minute.
In the function and disability analysis, greater hip abductor strength reduced the likelihood of poor chair stand rates (OR = 0.75; 95% CI, 0.59-0.95), as well as the inability to participate in major life tasks (OR = 0.68; 95% CI, 0.53-0.87) among patients with quadricep muscle strength that was equal to or greater than the overall mean quadricep strength normalized to body weight (0.82 Nm/kg). Although greater hip abductor strength did not have a significant impact on other disability measures, Chang said it appeared to be consistently protective. Meanwhile, there was no association between hip abductor strength and poor outcomes in patients with weaker quadricep strength.
When looking at cartilage damage worsening, greater hip abductor strength reduced the likelihood of poor tibiofemoral outcomes (OR = 0.73; 95% CI, 0.57-0.93) among participants with quadricep strength equal to or greater than the mean strength normalized to body weight (1.01 Nm/kg). It also had a nonsignificant beneficial effect on patellofemoral cartilage damage worsening. There was no association between hip abductor strength and outcomes in patients with weaker quadricep muscles.
For every 0.1 Nm/kg increase in baseline body weight-normalized hip abductor strength, Chang said there was a 25% to 32% reduced risk for poor chair stand and LLFDI frequency of participation outcomes at 5 years, as well as a 27% reduced risk for tibiofemoral cartilage damage worsening at 2 years.
“After stratification using median quadricep strength, we found that greater hip abductor strength appeared to confer additional beneficial effects on both joint health and long-term function and disability,” she said. “Our findings echo a recent meta-analysis of individuals with patellofemoral pain, suggesting that combined hip and knee strengthening over an average of 6 weeks resulted in greater pain relief and self-reported activity than knee strengthening alone. Improvements of combined hip and knee strengthening were maintained beyond the intervention period.”
Still, the current study had several limitations, according to Chang. She noted that a longer-term follow-up of structural knee worsening may be needed to elucidate the impact of hip abductor strengthening. In addition, most of the study participants were women (80%). Therefore, the results may not be generalizable to men. Finally, because there is no functional threshold for quadricep strength among patients with knee OA, the researchers used mean participant values as cutoff points.
“Although clinically relevant and important, these subgroup analyses by quadricep strength and by sex may have limited power for many comparisons of interest,” Chang said. – by Stephanie Viguers
Reference:
Chang AH, et al. Abstract 955. Presented at: ACR/ARHP Annual Meeting, Oct. 20-24, 2018; Chicago.
Disclosure: Chang reports no relevant financial disclosures.