Joints of the pectoral girdle

Joints of the Pectoral Girdle

The pectoral girdle connects the upper limb to the axial skeleton through a combination of synovial joints, ligaments, and muscular support. The major joints include:

  1. Sternoclavicular Joint (SC Joint)

  2. Acromioclavicular Joint (AC Joint)

  3. Glenohumeral Joint (shoulder joint, closely associated with the girdle).

1. Sternoclavicular Joint (SC Joint)

  • Type: Synovial saddle joint with a fibrocartilaginous articular disc.

  • Articulating Surfaces:

    • Sternal end of the clavicle.

    • Manubrium of the sternum.

    • First costal cartilage.

  • Ligaments:

    • Anterior and Posterior Sternoclavicular Ligaments: Reinforce the joint capsule.

    • Interclavicular Ligament: Connects the clavicles across the top of the manubrium.

    • Costoclavicular Ligament: Anchors the clavicle to the first rib, preventing excessive elevation.

  • Movements:

    • Elevation and depression.

    • Protraction and retraction.

    • Axial rotation.

  • Clinical Relevance:

    • Rarely dislocates due to strong ligamentous support but may suffer from arthritis or sprains.

2. Acromioclavicular Joint (AC Joint)

  • Type: Synovial plane joint.

  • Articulating Surfaces:

    • Acromial end of the clavicle.

    • Acromion of the scapula.

  • Ligaments:

    • Acromioclavicular Ligament: Strengthens the joint capsule.

    • Coracoclavicular Ligaments:

      • Trapezoid Ligament.

      • Conoid Ligament.

    • These ligaments stabilize the scapula by anchoring it to the clavicle.

  • Movements:

    • Small gliding and rotational movements, which adjust the scapula during shoulder motion.

  • Clinical Relevance:

    • AC Joint Dislocation ("Shoulder Separation"): Common in falls or trauma to the shoulder.

3. Glenohumeral Joint (Shoulder Joint)

  • Type: Synovial ball-and-socket joint.

  • Articulating Surfaces:

    • Head of the humerus.

    • Glenoid cavity of the scapula.

  • Stability Features:

    • Glenoid Labrum: A fibrocartilaginous rim deepening the cavity.

    • Capsule and Ligaments:

      • Glenohumeral Ligaments: Reinforce the capsule.

      • Coracoacromial Ligament: Prevents upward displacement of the humeral head.

    • Rotator Cuff Muscles: Provide dynamic stabilization.

  • Movements:

    • Flexion, extension, abduction, adduction, rotation, and circumduction.

  • Clinical Relevance:

    • Prone to dislocations due to shallow glenoid cavity and high mobility.

Functional Overview of the Joints

  • The SC Joint serves as the only direct skeletal connection between the pectoral girdle and the axial skeleton.

  • The AC Joint adjusts the scapula to enhance shoulder flexibility.

  • The Glenohumeral Joint, although not technically part of the girdle, relies heavily on the stability provided by the SC and AC joints and their associated ligaments and muscles.

Associated Structures

  • Subacromial Space: Protects the supraspinatus tendon and bursa.

  • Scapulothoracic Articulation (not a true joint): Enables gliding motion between the scapula and thoracic wall, essential for smooth arm movement.

Clinical Correlation

  • Frozen Shoulder (adhesive capsulitis): Affects the glenohumeral joint but may involve the girdle’s movement restrictions.

  • Shoulder Impingement Syndrome: Involves compression within the subacromial space, often affecting girdle mechanics.