Static foot posture and its relation to clinical variables in ankylosing spondylitis

Aim Postural abnormalities of the foot are common in rheumatic diseases. Static foot posture is a poorly studied clinical parameter in ankylosing spondylitis (AS). The aim of the study was to evaluate static foot posture in patients with AS and to determine the potential impact of clinical variables on foot posture. Method Fifty patients with AS and 40 age- and sex-matched healthy controls were enrolled in the study. Disease activity was measured using the Ankylosing Spondylitis Disease Activity Score. Axial mobility was evaluated with the Bath Ankylosing Spondylitis Metrology Index three-point answer scale. Functional status was assessed by the Bath Ankylosing Spondylitis Functional Index and Health Assessment Questionnaire-Disability Index. Enthesitis and foot posture were evaluated by the Maastricht Ankylosing Spondylitis Enthesitis Score (MASES) and Foot Posture Index-6, respectively. Results Patients with AS revealed significantly higher scores of foot posture index when compared with controls (P = 0.005). Abnormal foot posture (pronated and supinated) was more common in the patient group (P < 0.01). According to the multinomial logistic regression analysis, a higher MASES score was associated with supinated foot posture in AS patients (odds ratio 1.47, 95% confidence interval 1.03-2.09, P = 0.035). In addition, supinated foot posture was associated with enthesitis of the Achilles tendon (P = 0.002). Conclusion Enthesitis is related to deteriorated static foot posture in patients with AS. Enthesitis of the Achilles tendon is closely associated with the supinated foot posture.