Test-retest reliability and responsiveness of centre of pressure measurements in patients with hip osteoarthritis
Objective The aim of this study was to determine a set of measures for the evaluation of balance in patients suffering from hip osteoarthritis (OA) that were both reliable and responsive to change. Design Three groups of subjects; Healthy, hip OA patients without surgery, and hip OA with surgery (pre and post-surgery) were included in this study. Subjects had to perform balance tests in two positions: standard and narrowed stance. CoP-based measures test-retest reliability was assessed in hip OA without surgery group, responsiveness were assessed between all groups and between pre and post-surgery. Results Intraclass Correlation Coefficient (ICC) values from hip OA without surgery ranged from −0.03 to 0.9 for only five parameters (CoP path length, SD velocity, mean velocity, and antero-posterior Root Mean Square (RMSAP)) having values over 0.7. SD velocity and RMSAP showed significant differences between healthy and surgery group in standard stance whereas narrowed stance revealed most differences between all groups. RMSAP showed the best responsiveness (Standardized Response Mean ∼0.5) between pre vs post-surgery in both conditions. RMSAP was also capable of discriminating between hip OA with surgery vs without surgery groups with good sensitivity and specificity. Conclusions Our results showed there to be reliability and responsiveness of five postural parameters in hip OA patients in two conditions of standing balance. More parameters were significantly different in narrowed stance whereas sensitivity was better in standard stance. SD velocity and RMSAP discriminate between degrees of OA severity and highlight potential balance deficits even after arthroplasty. Selected parameters during standing balance could be assessed to complete the set of quantitative measures to quantify hip OA patient deficiencies.