Normal and abnormal motion of the shoulder

Abstract

he shoulder is a complex structure with various joints moving relative to each other to allow the large range of motion achieved. Previous studies have recommended that shoulder abduction be assessed in the plane of the scapula. This study assesses the angular movements of the humerus and scapula, examines where the centre of rotation of the humeral head lies and describes the excursion of the humeral head on the scapula during abduction, by way of radiographic study. Twenty-seven subjects; 12 normal controls and 15 patients with symptomatic shoulder problems were assessed. The study found that at less than 30° abduction, the ratio of gleno-humeral to scapulo-thoracic movement was 4.3:1, that is the scapula moved much less than the humerus; when abduction was greater than 30° this ratio changed to 5:4, that is the motion of the humerus and scapula were similar. At the same time, external rotation of the scapula was observed. In normal subjects the centre of rotation of the humeral head showed little variation (6 mm) through abduction and the excursion was small. If these parameters were abnormal the biomechanics of the shoulder were abnormal indicating a previous injury; this may be of clinical and diagnostic use.