Women with knee osteoarthritis who had low thigh muscle strength were more likely to need a knee replacement in a case-control study of participants in the Osteoarthritis Initiative (OAI).
In particular, predictors of knee replacement included knee extensor weakness in the year prior to knee replacement and longitudinal deterioration in knee extensor strength over a 2-year observation period prior to surgery. Measurement of knee extensor strength in women with knee osteoarthritis may then indicate who could benefit from weight training exercises to potentially delay or prevent the need for knee replacement surgery, said the researchers, led by Dr. Adam Culvenor of Paracelsus Medical University in Salzburg, Austria (Arthritis Rheumatol. 2015 Dec 14. doi: 10.1002/art.39540).
The optimal knee extensor strength threshold for differentiating those with and without knee replacement risk was approximately 200 N or 0.9 Nm/kg; or prevention of any loss of knee extensor strength over 2 years.
“There appears to be a considerable window for women below this threshold to obtain realistic strength gains and potentially lower the risk of knee replacement,” the study authors concluded.
In the multicenter, longitudinal, case-control study of 4,796 participants in the OAI (60% of whom were women), the investigators identified 136 participants who had received a knee replacement and matched them with controls who had not received a knee replacement and were similar in age, body mass index (BMI), and radiographic stage. The mean age of the women was 65 years and the mean BMI was 29 kg/m2.
The results showed that knee extensor strength at the examination prior to knee replacement (time T0), which occurred 2 years or less before surgery, was significantly lower in females who had received a knee replacement than in matched controls (pain-adjusted odds ratio, 1.72; 95% confidence interval, 1.16-2.56; P = .007). Measurement of the longitudinal change in knee extensor and flexor strength between T0 and 2 years prior to T0 (T-2) also provided similar results (pain-adjusted OR, 4.30; 95% CI, 1.34-13.79; P = .014). The findings were independent of age, BMI, and radiographic disease severity, the researchers noted.
The investigators found no relationship between knee extensor or flexor muscle strength in men and subsequent need for knee replacement surgery. The relationship between thigh muscle strength and knee replacement for women did not extend to measurements made at T-2 or T-4 or the change in thigh muscle strength between T-2 and T-4.
The OAI receives funding from the National Institutes of Health, Merck Research Laboratories, Novartis, GlaxoSmithKline, and Pfizer. The work was also funded by a grant from the European Union Seventh Framework Programme. One author disclosed consulting or preparing educational sessions for pharmaceutical companies and for receiving research support. Two authors reported being employees of Chondrometrics GmbH, a company providing MR image analysis services to academic researchers and to industry.