Scapular Dyskinesis is the alteration in the normal static or dynamic position or motion of the scapula during coupled scapulohumeral movements. Patterns of abnormal motion in scapular dyskinesis are best assessed by observing the scapular motion as arms are elevated and lowered in scapular plane.
Inferior angle (type I)
At rest, the inferior medial scapular border may be prominent dorsally. During arm motion, the inferior angle tilts dorsally and the acromion tilts ventrally over the top of the thorax. The axis of the rotation is in the horizontal plane.
Medial border (type II)
At rest, the entire medial border may be prominent dorsally. During arm motion, the medial scapular border tilts dorsally off the thorax. The axis of the rotation is vertical in the frontal plane.
Superior border (type III)
At rest, the superior border of the scapula may be elevated and the scapula can also be anteriorly displaced. During arm motion, a shoulder shrug initiates movement without significant winging of the scapula occurring. The axis of this motion occurs in the sagittal plane.
Symmetric scapulohumeral (type IV)
At rest, the position of both scapula are relatively symmetrical, taking into account that the dominant arm may be slightly lower. During arm motion, the scapulae rotate symmetrically upward such that the inferior angles translate laterally away from the midline and the scapular medial border remains flush against the thoracic wall. The reverse occurs during lowering of the arm.