This study used bone-fixed transcortical pins in the clavicle, scapula, and humerus to track true 3D motion of all four shoulder joints during arm elevation. It describes normal sternoclavicular, acromioclavicular, scapulothoracic, and glenohumeral motion across flexion, scapular, and coronal planes. The goal was to establish reference kinematics for identifying and treating shoulder motion abnormalities.
When you assess a patient for scapular dyskinesia, this paper is why you can watch the arm coming down: normal joint angles are nearly identical during raising and lowering, so an abnormal lowering pattern is genuinely pathologic. The 2:1 scapulohumeral rhythm is the reference you carry into every shoulder exam. Deviation from it flags an abnormal scapular contribution to elevation.
Two mechanical pearls anchor cuff and impingement pathology. Reduced scapulothoracic posterior tilt narrows the subacromial space, and progressive glenohumeral external rotation during elevation explains why supraspinatus tears preserve elevation until they extend into the infraspinatus.
Remember the linkage principle: the scapula only moves on the thorax through combined SC and AC motion, and clavicular posterior rotation is passive. This is why AC or SC pathology alters overhead motion and why stabilization procedures must respect these coupled rotations.
This study used bone-fixed transcortical pins in the clavicle, scapula, and humerus to track true 3D motion of all four shoulder joints during arm elevation. It describes normal sternoclavicular, acromioclavicular, scapulothoracic, and glenohumeral motion across flexion, scapular, and coronal planes. The goal was to establish reference kinematics for identifying and treating shoulder motion abnormalities.
When you assess a patient for scapular dyskinesia, this paper is why you can watch the arm coming down: normal joint angles are nearly identical during raising and lowering, so an abnormal lowering pattern is genuinely pathologic. The 2:1 scapulohumeral rhythm is the reference you carry into every shoulder exam. Deviation from it flags an abnormal scapular contribution to elevation.
Two mechanical pearls anchor cuff and impingement pathology. Reduced scapulothoracic posterior tilt narrows the subacromial space, and progressive glenohumeral external rotation during elevation explains why supraspinatus tears preserve elevation until they extend into the infraspinatus.
Remember the linkage principle: the scapula only moves on the thorax through combined SC and AC motion, and clavicular posterior rotation is passive. This is why AC or SC pathology alters overhead motion and why stabilization procedures must respect these coupled rotations.