Shoulder Kinesiology

The shoulder complex consists of four joints that work together to allow movement:

  1. Glenohumeral (GH) Joint – Ball-and-socket joint allowing flexion, extension, abduction, adduction, rotation, and circumduction.

  2. Sternoclavicular (SC) Joint – Connects the clavicle to the sternum, allowing elevation, depression, protraction, retraction, and rotation of the clavicle.

  3. Acromioclavicular (AC) Joint – Provides stability between the acromion and clavicle, playing a role in scapular motion.

  4. Scapulothoracic Joint (not a true joint) – Facilitates scapular movements like protraction, retraction, upward/downward rotation, elevation, and depression.

Key Movements & Muscles Involved

  • Flexion: Anterior deltoid, pectoralis major (clavicular head), coracobrachialis, biceps brachii

  • Extension: Posterior deltoid, latissimus dorsi, teres major, triceps brachii (long head)

  • Abduction: Supraspinatus, deltoid (middle fibers)

  • Adduction: Pectoralis major, latissimus dorsi, teres major

  • External Rotation: Infraspinatus, teres minor, posterior deltoid

  • Internal Rotation: Subscapularis, teres major, pectoralis major, latissimus dorsi, anterior deltoid

  • Scapulohumeral Rhythm: For every 2° of humeral movement, the scapula moves 1° to maintain stability and function.

Shoulder Ligaments & Their Functions

  1. Glenohumeral Ligaments (GHL)

    • Superior GHL: Prevents inferior displacement of the humeral head.

    • Middle GHL: Resists anterior translation of the humeral head at mid-range abduction.

    • Inferior GHL: Supports the joint at high abduction angles, resisting anterior and posterior dislocations.

  2. Coracohumeral Ligament (CHL)

    • Prevents excessive inferior displacement of the humeral head.

    • Helps limit external rotation at lower degrees of abduction.

  3. Coracoacromial Ligament (CAL)

    • Forms the coracoacromial arch, preventing superior displacement of the humeral head.

    • Involved in shoulder impingement syndrome when inflamed.

  4. Acromioclavicular Ligaments (ACL)

    • Reinforces the AC joint to prevent excessive movement.

    • Superior & Inferior AC Ligaments stabilize the acromioclavicular connection.

  5. Coracoclavicular Ligaments (CCL)

    • Trapezoid Ligament – Resists lateral displacement of the clavicle.

    • Conoid Ligament – Prevents excessive superior movement of the clavicle.

    • Important for shoulder suspension mechanics and clavicle stability.

  6. Transverse Humeral Ligament

    • Holds the long head of the biceps tendon within the bicipital groove.

Clinical Relevance

  • Shoulder Dislocations: Typically occur anteriorly, where the inferior GHL is most vulnerable.

  • Rotator Cuff Injuries: Weakness or tears in supraspinatus, infraspinatus, teres minor, or subscapularis can affect shoulder stability.

  • Shoulder Impingement: Narrowing of the subacromial space can compress the supraspinatus tendon and subacromial bursa.

  • AC Joint Sprains: Injuries to the coracoclavicular ligaments can result in AC joint separation.

Here are some possible exam questions covering the shoulder kinesiology and ligaments:

Multiple Choice Questions (MCQs)

  1. Which of the following ligaments forms the coracoacromial arch and helps prevent superior displacement of the humeral head?
    a) Coracoclavicular ligament
    b) Coracohumeral ligament
    c) Coracoacromial ligament
    d) Inferior glenohumeral ligament

  2. The scapulohumeral rhythm describes the coordinated movement between the:
    a) Sternoclavicular and acromioclavicular joints
    b) Glenohumeral and scapulothoracic joints
    c) Humeroulnar and radiocarpal joints
    d) Sternocostal and glenohumeral joints

  3. Which muscle is NOT primarily responsible for shoulder external rotation?
    a) Infraspinatus
    b) Teres minor
    c) Subscapularis
    d) Posterior deltoid

  4. The inferior glenohumeral ligament (IGHL) is most important for preventing:
    a) Anterior dislocation at 90° abduction
    b) Posterior dislocation during flexion
    c) Inferior translation at rest
    d) Clavicular elevation

  5. Damage to the long thoracic nerve would most likely result in:
    a) Weakness in shoulder flexion
    b) Scapular winging
    c) Loss of external rotation
    d) Inability to abduct beyond 90°

Here are the answers to the possible exam questions on the shoulder kinesiology and ligaments:

Multiple Choice Questions (MCQs) - Answers

  1. Which of the following ligaments forms the coracoacromial arch and helps prevent superior displacement of the humeral head?
    Answer: c) Coracoacromial ligament

  2. The scapulohumeral rhythm describes the coordinated movement between the:
    Answer: b) Glenohumeral and scapulothoracic joints

  3. Which muscle is NOT primarily responsible for shoulder external rotation?
    Answer: c) Subscapularis (Subscapularis is responsible for internal rotation, while infraspinatus, teres minor, and posterior deltoid perform external rotation.)

  4. The inferior glenohumeral ligament (IGHL) is most important for preventing:
    Answer: a) Anterior dislocation at 90° abduction

  5. Damage to the long thoracic nerve would most likely result in:
    Answer: b) Scapular winging (Due to weakness of the serratus anterior muscle.)