Anatomy of the Shoulder

Anatomy of the Shoulder

Four muscles termed the rotator cuff muscles that stabilise the joint by producing medially directed forces surround the glenohumeral joint.

The articular contact is very small and is steadied by the presence of a cartilaginous rim termed the labrum. The labrum deepens the glenoid fossa (the articular surface of the scapula); to hold the head of the humerus in place whilst compressive forces are applied by the muscles.

Of the six muscles, four comprise the rotator cuff: the Supraspinatus, Infraspinatus (both innervated by the suprascapular nerve), Teres Minor (axillary nerve), and the Subscapularis (innervated by the upper and lower subscapularis nerves).

These short muscles originate on the scapula and pass around the shoulder where their tendons join, attaching to the capsular ligament of the glenohumeral joint and forming the rotator cuff of the shoulder.

 

Image of the glenohumeral joint showing rotator cuff muscles

 

The primary supporting ligamentous structure in the shoulder joint is the capsule, a tough fibrous sheath that attaches proximally around the articular edge of the glenoid fossa and distally at the anatomical neck of the humerus. The capsule functions to resist undesirable humeral translations usually in end range movements of the shoulder.

Other important ligaments of the shoulder include the coraco-clavicular ligament that attaches between the coracoid process and the clavicle. It consists of two parts, a medial portion called the conoid, and the trapezoid, which lies slightly lateral to the conoid. The coracoacromial ligament attaches between the coracoid process and the acromion and the coraco-humeral ligament attaches between the humerus and coracoid process. Finally the superior transverse scapular ligament lies slightly medial to the conoid part of the coraco-clavicular ligament and forms a strong fibrous band that bridges the subscapular notch.

Image of ligaments of the glenohumeral joint