Scapular mobility plays a central role in normal shoulder function, and alterations in scapular mobility have been suggested as a factor in impingement syndrome. We therefore measured the effect of restricted scapular mobility during arm abduction on acromiohumeral and coracohumeral distances. For the control measurements, healthy volunteers (n = 10, all male, age range 25-35 years) underwent multislice computed tomography in a supine position, with the humerus actively maintained in the scapular plane at 45 degrees internal rotation and 60, 90 or 120 degrees abduction. To restrict scapular mobility a custom-made brace was then placed on each volunteer and fastened firmly with bandages, and the measurements were repeated. From the three-dimensional images the acromiohumeral and coracohumeral distances were measured. With the humerus in 90 degrees abduction, the acromiohumeral distance was significantly reduced (Student's t test). This result suggests that impingement syndrome may have a functional component.