Rotator Cuff Biomechanics

The aim of this presentation is to discuss the current literature and opinions on the biomechanics of the rotator cuff and relate this to the clinical relevance in rotator cuff tears. I intend to cover: Relate Biomechanics to Clinical Relevance 1. Cuff Mechanics 2. Tendon Anatomy – layers, microanatomy, blood supply 3. Pathomechanics of cuff tears The shoulder complex comprises 30 muscles. These muscles both move the shoulder and stabilise it – 'movers' and 'shakers'. The rotator cuff muscles predominantly stabilise the glenohumeral joint, but also contribute significantly to movement. The rotator cuff muscles are: 1. Supraspinatus 2. Infraspinatus 3. Teres Minor 4. Subscapularis The tendons of these muscle coalesce to form the rotator cuff. The muscles are inseparable at this level, except for subscapularis which is separate and joined to the rest of the cuff via the rotator interval. Supraspinatus Supraspinatus is not only an initiator of abduction, but acts throughout the range of abduction of the shoulder. It has equal abduction power as deltoid. Note that it lies in the scapular plane – i.e. 30 degrees to the coronal plane (Figure 2). These two muscles lies below the scapular spine and are external rotators of the shoulder. Infraspinatus primarily acts with the arm in neutral and Teres Minor is more active with external rotation in 90 degrees of abduction.