Evaluation of dynamic postural balance using the Biodex Stability System in rheumatoid arthritis patients

The aim of this study was to investigate dynamic postural balance in patients with rheumatoid arthritis (RA) in relation to the disease characteristics. Seventy-four patients with RA and 42 controls of the same age group were tested using the Biodex Stability System (Biodex Medical Systems, Shirley, NY, USA). Anterior/posterior (AP), medial/lateral (ML), and overall (OA) indices were obtained with bilateral stance at platform stabilities of 2 and 8. Subjects were tested with "eyes open" at all times. At the same time, Disease Activity Score, functional disability [Health Assessment Questionnaire, (HAQ)], and Steinbrocker Functional Class (SFC) were assessed. Both the AP and OA indices in the RA group were significantly higher than in the control group for level 8. For OA index, the results were 2.7+/-0.9 in RA and 2.2+/-0.7 in the control group (p=0.006), and for AP index, the results were 2.1+/-0.7 in RA and 1.7+/-0.6 in the control group (p=0.002). Eleven patients (15.9%) and three controls (7.1%) could not complete the test at level 2. When the patients and controls who completed the test were compared, a significant difference was found only in the ML index. The results were 4.6+/-2.4 in RA and 3.8+/-1.6 in the control group (p=0.047). A positive correlation between HAQ and postural balance for all three stability indices at level 8 was detected. A positive correlation between SFC and postural balance for OA and ML at level 8 was also found. Multiple linear regression analyses revealed age and body mass index (BMI) to be the most important factors influencing postural dynamic balance at both levels in the RA group and in healthy controls. RA has a negative effect on dynamic postural stability. The functional status affects dynamic balance more than disease activity. Age and BMI were the most important factors influencing postural dynamic balance in the RA group and in healthy controls. Level 2 does not appear to be an appropriate level for evaluating postural stability in RA.