The Shoulder Joint

• Ball and socket, synovial, circumduction and rotation

• Covered by articular capsule which is weakest at inferiorly.

  • capsule has two apertures

• one opening between the tubercles of the humerus for passage of long head of biceps brachii,

• other opening is anterior, inferior to corocoid process. Allows communication between subscapular bursa and synovial cavity of joint.

• Glenoid labrum – ring of fibro-cartilage that runs round cavity of the scapula. It deepens this cavity and effectively increases the surface of the shoulder joint.

• Ligaments of shoulder joint

• Stability of shoulder joint – free movement of the joint leads to instability. Strength is provided by rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis SITS)

  • Rupture of rotator cuff

  • Dislocation of shoulder joint – due to its free movement, shoulder joint commonly dislocated.

    • Anterior dislocation occurs most often in young adults, athletes. Caused by excessive extension and lateral rotation of humerus. The head of the humerus is driven anteriorly, usually taking with it the fibrous capsule and glenoid labrum. Diagnosed on AP X-ray.

    • Posterior dislocation –blow to an arm which is abducted and medially rotated, tilting the humeral head inferiorly, tearing the weak inferior area of the articular capsule, so that the head of the humerus lies inferior to the glenoid cavity. Common in epileptics and electrocutions. Light bulb sign on AP X-ray, diagnosis made on axillary view.

    • Axillary nerve may be damaged in shoulder dislocation, indicated by paralysis of deltoid.

• Subscapular bursa – between tendon of subscapular muscle and neck of scapula. Communicates with cavity of shoulder through an opening in its fibrous cavity

• Subacromial bursa – lies between deltoid, supraspinatus tendon and fibrous capsule. Does not communicate with cavity of shoulder. Facilitates movement of deltoid over the fibrous capsule of the shoulder joint and the supraspinatus tendon.

  • Calcific supraspinatus tendonitis = inflammation and calcification of subacromial bursa resulting in pain, tenderness and limitation of movement of shoulder joint.

• Blood supply: articular arteries which are branches of anterior and posterior circumflex humeral arteries from the axillary and suprascapular artery from the subclavian.

• Nerve supply: articular nerves which are branches of suprascapular, axillary, lateral pectoral nerves

Category: Anatomy Notes