Patients and methods: The cross-sectional observational study enrolled 32 AS patients (23 males, 9 females; mean age: 39.4±7.2 years; range, 18 to 65 years) diagnosed according to the modified New York criteria and 32 healthy controls (22 males, 10 females; mean age: 36.6±7.5 years; range, 18 to 65 years) between April 2017 and October 2018. Plantar center of pressure (CoP) excursions were recorded using a pressure platform to evaluate postural stability. The thickness of the lumbar multifidus and gastrocnemius muscles was measured using ultrasound.

Results: Patients with AS showed reduced muscle thickness at the multifidus (p<0.05) muscle and medial gastrocnemius (p=0.002) and lateral gastrocnemius (p=0.002) muscles compared to controls. Increased CoP excursions were observed only in the anteroposterior direction in the double-leg (standard) stance with the eyes closed (p=0.003) and in both anteroposterior and mediolateral directions in tandem and single-leg stances (all p<0.05). Center of pressure excursions in standard stance with the eyes closed were negatively correlated with all muscle thickness values (all p<0.05). In the single-leg stance, CoP excursions were negatively correlated with muscle thickness of medial gastrocnemius (p=0.008) and lateral G (p=0.016) muscles.

Conclusion: Early planning of exercise programs taking muscle loss into account can help improve balance and thereby prevent falls and fractures in AS patients. Keywords : Ankylosing spondylitis, multifidus, postural balance, ultrasonography