Background Muscular control of the knee is a vital aspect of living with knee osteoarthritis (OA). There is consistent evidence that OA patients have reduced strength in knee flexion and knee extension, while studies of hip abduction and hip adduction in knee OA patinets present somewhat inconsistent findings. These inconsistencies make room for doubt in clinical practice.
Objectives To compare muscle strength in patients with knee OA and healthy controls and investigate whether the same pattern of weakness appears in subjects with bilateral versus unilateral knee OA.
Methods 51 female patients were included; 10 with bilateral knee OA, 26 unilaterally affected (13 right side, 13 left side) and 15 healthy controls (HC). All patients were examined by an orthopaedic surgeon and the diagnosis was verified clinically and radiographically prior to testing. Four test s of maximum isometric strength (maximum voluntary contraction (MVC)) were performed: hip abduction, hip adduction, knee flexion, and knee extension. Each test was performed three times, and the highest score was used in the analyses. Comparisons between groups were performed with t-tests or analysis of variance.
Results OA patients, when analysed as one group, were significantly weaker than HC in flexion (p<0.05 both sides), extension (p<0.05) right, p<.05 left), abduction left side (p<0.05), and adduction right side (p<0.05), but not in adduction left side (p=0,1) and abduction right side (p=0,2). When splitting the OA patients in unilateral and bilateral affection, the unilateral group were significantly weaker than HC in all tests (p<0.001 to p<0.05), while the bilaterally affected group were significantly weaker in flexion (p<0.05) and extension (p<0.05), but not in adduction (p=1) and abduction (p=1).
Conclusions Patients with bilateral knee OA seem to have a different pattern of muscle strength reduction than the unilaterally affected patients. The bilaterally affected OA patients were not significantly weaker than healthy controls in abduction and adduction of the hip. Analysing muscle strength in patients with unilateral- and bilateral knee OA as one group, can give biased results due to different pattern of weakness, and may explain the inconsistent findings in earlier studies. Further research with larger sample sizes is needed to confirm these findings.
Disclosure of Interest None Declared
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