Scapulohumeral rhythm and associated spinal motion.

Background: To investigate the coordination of humeral, scapular and thoracolumbar spine motions during a number of unilateral and bilateral upper limb movements in a range of movement conditions.

Methods: Thirty-two healthy women performed unilateral and bilateral arm elevations in three planes-sagittal, coronal and scapular. Scapular, humeral and spinal orientations were measured at 100 Hz using a multi-sensor, 6-degree-of-freedom electromagnetic tracking system. Segmental displacements were computed following International Society of Biomechanics recommendations.

Findings: Humeral, scapular and thoracic segments demonstrate consistent, synchronous interactions. Scapular upward rotation is significantly greater on the non-dominant side than the dominant in all planes of movement and in both unilateral and bilateral arm movement. Unilateral and bilateral arm movements produce significantly different ranges and patterns of spinal motion and ranges of scapular external rotation. There does not appear to be any effect of age, height or weight on the ranges or patterns of motion of the shoulder girdle and spine during arm elevation.

Interpretation: Movement of the arm into elevation, irrespective of the plane of motion, has significant implications for the shoulder girdle and the thoracic spine. Clinical assessment of the shoulder should include the thoracic spine.