Humeroscapular positions in a shoulder range-of-motion-examination

Positions of the arm are traditionally described in relation to the thorax. Yet shoulder pathology most often lies in and about the glenohumeral joint, which then becomes the focus of treatment. Little is known about the relative motion between the humerus and the scapula primarily because there is no clinically accepted method for assessing and describing these positions. This paper proposes a clinical method for describing and measuring humeroscapular positions based on an anatomic definition of the plane of the scapula. Humeroscapular positions achieved by 75 normal subiects during a conventional (humerothoracic) shoulder range-of-motion examination are presented. Identification of the plane of the scapula is based on four palpable anatomic landmarks: (7) the inferior pole of the scapula, (2) the medial border of the scapula at the level of the scapular spine, (3) the posterolateral corner of the acromion, and (4) the tip of the coracoid. The plane of the scapula is defined by the line connecting the first two of these points and a point midway between the last two. Humeroscapular positions are specified by the plane of elevation and the angle of elevation in relation to this mobile scapular plane. Measurement of these positions was done with a goniometer facilitated by a "scapula-locating device" designed for this study. Maximal humerothoracic elevation of the arm was achieved with the humerus lust behind the scapular plane at 90° of humeroscapular elevation. Cross-body adduction positioned the humerus in a plane 51° anterior to the plane of the scapula, with most of the cross-body motion occurring between the scapula and thorax. External rotation at 90° of elevation in the coronal plane of the body (the apprehension position) positioned the humerus in a plane 17° posterior to the scapular plane. Humerothoracic extension and reaching up the back took place at very low angles of humeroscapular elevation.