Comparison of shoulder muscle strength, shoulder range of motion and scapular motion in men with ankylosing spondylitis and healthy men: a case-controlled study

Ankylosing spondylitis mainly affects the vertebral column, meaning that the assessment of the physical function of the upper extremity and scapulothoracic region in ankylosing spondylitis is often overlooked. Therefore, the aim of this study was to investigate shoulder muscle strength, shoulder active range of motion and three-dimensional scapular motion in patients with ankylosing spondylitis. The study included 18 men with ankylosing spondylitis, and 16 age-matched typically healthy men as the control group. Muscle strength, active range of motion, and three-dimensional scapular motion were assessed with a digital hand-held dynamometer, an inclinometer, and an electromagnetic tracking device respectively. A decrease in shoulder flexion and abduction muscle strength on both the dominant side (P<0.001, P=0.001) and non-dominant side (P<0.001, P<0.001) was found in the ankylosing spondylitis group compared to the control group. A decrease in shoulder flexion, abduction, and external and internal rotation active range of motion on both the dominant side (P=0.001, P<0.001, P=0.015, P<0.001, respectively) and non-dominant side (P=0.001, P<0.001, P=0.017, P<0.001 respectively) was observed in the ankylosing spondylitis group. There was an increase in the upward rotation of the scapula on the non-dominant side at 30, 60, and 90° humeral elevations in the ankylosing spondylitis group compared to the control group (P=0.018, P=0.003, P=0.001 respectively). The other parameters of the scapular motion did not differ between groups (P>0.05). This study showed that shoulder muscle strength and active range of motion were lower, and the upward rotation of the scapula was greater in men with ankylosing spondylitis compared to typically healthy men. The kinetics and kinematics parameters of the shoulder and scapula should be considered when assessing the physical function of patients with ankylosing spondylitis.