joint

Shoulder Joint Overview

  • Type of Joint: Ball-and-socket
      - Humeral head articulates with the glenoid fossa of the scapula.
      - Movement is possible in all three planes around all three axes, making it the most movable joint in the body, but it is also one of the least stable.

Movements of the Shoulder Joint

  • Types of movements:
      - Flexion: Moving the arm forward away from the body.
      - Extension: Moving the arm backward.
      - Hyperextension: Extending the arm beyond the normal range.
      - Abduction: Moving the arm away from the midline of the body.
      - Adduction: Bringing the arm toward the midline of the body.
      - Medial (internal) rotation: Rotating the arm toward the body.
      - Lateral (external) rotation: Rotating the arm away from the body.
      - Horizontal abduction: Moving the arm horizontally away from the body.
      - Horizontal adduction: Bringing the arm horizontally toward the body.
      - Scaption: A movement between flexion and abduction, typically at a 30-degree angle from the body.

Bones and Landmarks

  • Key Structures:
      - Acromion Process: The bony prominence on the scapula.
      - Infraspinous Fossa: Part of the scapula located below the spine of the scapula.
      - Supraspinous Fossa: Part of the scapula located above the spine of the scapula.
      - Glenoid Fossa: The shallow cavity in the scapula that articulates with the humeral head.
      - Labrum: Cartilaginous structure that deepens the glenoid cavity.
      - Axillary/Vertebral Borders: Edges of the scapula, important for landmark identification.
      - Subscapular Fossa: The anterior surface of the scapula, which gives attachment to the subscapularis muscle.

Ligaments and Other Structures

  • Important Ligaments:
      - Coracohumeral Ligament: Connects the coracoid process to the humeral head, providing support.
      - Glenohumeral Ligaments: A group of ligaments that reinforce the shoulder joint capsule.
      - Coracoclavicular Ligament: Connects the coracoid process to the clavicle, stabilizing the acromioclavicular joint.
      - Coracoacromial Ligament: Provides an arch over the shoulder joint.

  • Shoulder Joint Capsule: Encloses and stabilizes the shoulder joint.

  • Tendons:
      - Tendon of the Long Head of the Biceps: Stabilizes the shoulder joint and aids in movement.

Shoulder Muscles

  • Deltoid Muscle:
      - Origin:
        - Anterior part: Lateral 1/3 of clavicle.
        - Middle part: Acromion process.
        - Posterior part: Spine of scapula.
      - Insertion: Deltoid tuberosity of the humerus.
      - Actions:
        - Anterior: Shoulder flexion, medial rotation, horizontal adduction, abduction.
        - Middle: Abduction.
        - Posterior: Shoulder extension, lateral rotation, horizontal abduction, abduction, hyperextension.
      - Nerve Supply: Axillary nerve (C5, C6).

  • Pectoralis Major:
      - Origin:
        - Clavicular Portion: Medial 1/3 of clavicle.
        - Sternal Portion: Sternum and costal cartilage of ribs 1-6.
      - Insertion: Lateral lip of the bicipital groove.
      - Actions:
        - Clavicular Portion: Shoulder flexion to about 60°.
        - Sternal Portion: Shoulder extension to about 120°.
        - Together: Shoulder adduction, medial rotation, horizontal adduction.
      - Nerve Supply: Lateral and medial pectoral nerves (C5-T1).

  • Latissimus Dorsi:
      - Origin: Spinous processes of T7-L5, posterior surface of sacrum, iliac crest, lower three ribs (via dorsolumbar fascia).
      - Insertion: Medial floor (lip) of the bicipital groove of humerus.
      - Actions: Shoulder extension, adduction, medial rotation, hyperextension.
      - Nerve Supply: Thoracodorsal nerve (C6, C7, C8).

  • Teres Major:
      - Origin: Axillary border of scapula near inferior angle.
      - Insertion: Crest below lesser tubercle, inferior to latissimus dorsi insertion.
      - Actions: Shoulder extension, adduction, medial rotation.
      - Nerve Supply: Lower subscapular nerve (C5, C6).

  • Supraspinatus:
      - Origin: Supraspinous fossa of scapula.
      - Insertion: Greater tubercle of humerus.
      - Actions: Shoulder abduction to 90°.
      - Nerve Supply: Suprascapular nerve (C5, C6).

  • Infraspinatus:
      - Origin: Infraspinous fossa of scapula.
      - Insertion: Greater tubercle of humerus.
      - Actions: Shoulder lateral rotation, horizontal abduction.
      - Nerve Supply: Suprascapular nerve (C5, C6).

  • Teres Minor:
      - Origin: Axillary border of scapula.
      - Insertion: Greater tubercle of humerus.
      - Actions: Shoulder lateral rotation, horizontal abduction.
      - Nerve Supply: Axillary nerve (C5, C6).

  • Subscapularis:
      - Origin: Subscapular fossa of scapula.
      - Insertion: Lesser tubercle of humerus.
      - Actions: Shoulder medial rotation.
      - Nerve Supply: Upper and lower subscapular nerves (C5, C6).

  • Coracobrachialis:
      - Origin: Coracoid process of the scapula.
      - Insertion: Medial surface of humerus, middle.
      - Action: Stabilizes the shoulder joint.
      - Nerve Supply: Musculocutaneous nerve (C6, C7).

Rotator Cuff

  • Definition: A group of muscles and their tendons that act to stabilize and move the shoulder joint. It is comprised of four muscles:
      - Supraspinatus
      - Infraspinatus
      - Teres Minor
      - Subscapularis

  • Function: Blending together of these tendons reinforces the joint capsule and keeps the humerus rotating against the glenoid fossa.

Glenohumeral Movement

  • Types of Glenohumeral Motion:
      - Roll: The humeral head rolls on the glenoid surface.
      - Glide: The humeral head glides in the socket during movement.
      - Spin: The humeral head spins within the socket during certain movements.

  • Scapulohumeral Rhythm: The coordinated movement of the scapula and humerus during shoulder motions.

Shoulder Conditions

  • AC (Acromioclavicular) Separation: Injury to the AC joint.
      - Grade 1: AC ligament stretched.
      - Grade 2: AC ligament ruptured, coracoclavicular ligament stretched.
      - Grade 3: Both ligaments ruptured.

  • Fractures:
      - Clavicle Fractures: Common in children due to falling on the lateral shoulder.
      - Humeral Neck Fractures: Common in older adults with a FOOSH (fall on outstretched hand).
      - Mid Humeral Fractures: Often result from twisting injuries, associated with radial nerve injury.

  • Dislocation:
      - Anterior Dislocation: Often results from forced shoulder abduction and lateral rotation, causing the head of the humerus to slide out of the glenoid fossa.

  • Shoulder Subluxation: Partial dislocation where the head of the humerus slides out of the fossa but the capsule remains intact.

Shoulder Impingement

  • Definition: A condition where overuse leads to compression of structures between the acromion and the humeral head, often leading to inflammation.

  • Common Causes: Bone spurs, frayed muscles, inflamed bursa.

Adhesive Capsulitis (Frozen Shoulder)

  • Definition: A condition characterized by adhesions and scarring of the shoulder joint capsule, leading to restricted shoulder mobility.

Rotator Cuff Tears

  • Causes: Can be due to acute trauma or gradual degeneration over time. The supraspinatus tendon is the most frequently torn site.

Tendonitis

  • Definition: Inflammation of the tendon, commonly the long head of the biceps in its groove, which can lead to subluxation out of the groove.