Shoulder Joint Anatomy Quiz

Shoulder Joint Anatomy

• The shoulder joint (glenohumeral joint) is a ball-and-socket synovial joint formed between the glenoid cavity of the scapula and the head of the humerus.
• The joint is stabilized by a fibrous capsule, ligaments, and the rotator cuff muscles.
• Capsule:
  • Attached to the glenoid labrum, scapula, and the anatomical head of the humerus.
  • Thickened by three glenohumeral ligaments anteriorly and a coracohumeral ligament superiorly.
  • Contains two openings:
    • One for communication with the subscapular bursa, which facilitates the movement of the subscapularis tendon.
    • Another for the passage of the long head of the biceps brachii tendon.
• Ligaments:
  • Intracapsular:
    • Superior, middle, and inferior glenohumeral ligaments: Reinforce the capsule anteriorly.
  • Extracapsular:
    • Coracoacromial ligament: Links the acromion and coracoid process.
    • Coracohumeral ligament: Passes from the base of the coracoid process to the anterior part of the greater tubercle of the humerus.
    • Transverse humeral ligament: Holds the tendon of the long head of the biceps in place during shoulder movement.

The Coracoacromial Arch

• A strong osseoligamentous structure that provides a smooth under-surface for the acromion, coracoacromial ligament, and coracoid process.
• Overlies the humeral head and prevents superior displacement of the humerus.
• Separated from the supraspinatus tendon by the subacromial bursa.
• Contains: subacromial bursa, rotator cuff tendons, tendon of the long head of the biceps.
• Risk of soft tissue impingement between the head of the humerus and the acromion during abduction.

Bursae around the Glenohumeral Joint

• Subscapular bursa: Facilitates the movement of the tendon of the subscapularis over the scapula.
• Subacromial bursa: Facilitates the movement of the supraspinatus tendon under the coracoacromial arch and the deltoid muscle over the shoulder joint and the greater tubercle of the humerus.
• Inflammation of bursae: Can lead to:
  • Subacromial bursitis: Pain on abduction of the arm between 50-130 degrees.

Movements of the Glenohumeral Joint

• Flexion: Pectoralis major, anterior fibers of deltoid, coracobrachialis, and biceps brachii.
• Extension: Latissimus dorsi and the posterior fibers of the deltoid.
• Abduction:
  • Supraspinatus (initiator up to 15-20 degrees).
  • Central deltoid fibers (20-90 degrees).
  • Rotation of the scapula by trapezius and serratus anterior (above 90 degrees).

Neurovascular Supply of the Glenohumeral Joint

• Blood supply: Anterior and posterior circumflex humeral arteries, suprascapular artery.
• Innervation: Suprascapular, axillary, and lateral pectoral nerves.
  • All from brachial plexus roots C5 and C6.
  • Upper brachial plexus injuries can affect shoulder movement.

Clinical Application

• Axillary nerve and circumflex artery: Vulnerable during intramuscular injections and shoulder dislocation.
• Rotator cuff problems:
  • Tendons rubbing under the coracoacromial arch can cause irritation and inflammation.
  • Can lead to subacromial bursitis, supraspinatus tendonitis, rotator cuff injury, degeneration or rupture of tendons.
• Causes of rotator cuff injuries: Overuse, degenerative changes in tendons (older people), avascularity of the supraspinatus tendon, anatomical variation.
• Rotator cuff problems result in: Painful arc/impingement syndrome (pain on abduction of the arm between 70-120 degrees).

Stability of the Glenohumeral Joint

• Provided by:
  • Rotator cuff tendons (anteriorly, posteriorly, superiorly).
  • Glenohumeral intracapsular ligaments (anteriorly, inferiorly).
  • Coracohumeral ligament (superiorly).
  • Coracoacromial arch (superiorly).
  • Glenoid labrum deepening of the glenoid cavity.
  • Splinting effect of the long head of biceps above and the long head of triceps below.

Glenohumeral Joint Dislocation

• Most common type: Inferior dislocation, clinically defined as anterior dislocation due to the humeral head locating anteriorly.
• Mechanism: Pectoralis major pulling the arm anteriorly.
• Complications: Capsule and rotator cuff tendon tears.
• Recurrent dislocation: Can occur if tears heal poorly.

Axillary Nerve Injury

• Can be injured during dislocation due to its proximity to the inferior part of the joint capsule.
• Signs:
  • Deltoid muscle paralysis with loss of abduction.
  • Loss of sensation in a small area of skin over the central part of the deltoid ("regimental badge area").

Adhesive Capsulitis (Frozen Shoulder)

• Cause: Adhesive fibrosis and scarring between the inflamed capsule, rotator cuff, subacromial bursa, and deltoid.
• Symptoms:
  • Difficulty abducting the arm.
  • Lack of movement in the glenohumeral joint.
  • Pain when elevating the shoulder.
• Causes: Dislocation, rotator cuff tears, calcific supraspinatus tendonitis, bicipital tendonitis.

Glenoid Labrum Tears

• Common in: Athletes and individuals with shoulder instability and partial dislocation.
• Symptoms: Pain, popping/snapping feeling.

Osteoarthritis of the Glenohumeral Joint

• Relatively uncommon: Cause of shoulder complaints.
• Cause: Degenerative changes of articular cartilage.
• Often secondary to: Trauma (dislocation, humeral head fracture, large rotator cuff tears).
• Primary osteoarthritis: More common in women and those over 60.
• Symptoms: Similar to frozen shoulder, with pain predominating.
• Diagnosis: X-rays.