Shoulder Kinesiology

Glenohumeral (GH) Joint

A ball-and-socket joint allowing flexion, extension, abduction, adduction, rotation, and circumduction.

Sternoclavicular (SC) Joint

Connects the clavicle to the sternum, allowing elevation, depression, protraction, retraction, and rotation of the clavicle.

Acromioclavicular (AC) Joint

Provides stability between the acromion and clavicle, playing a role in scapular motion.

Scapulothoracic Joint

Not a true joint; facilitates scapular movements like protraction, retraction, upward/downward rotation, elevation, and depression.

Flexion (of the shoulder)

Movement involving the anterior deltoid, pectoralis major (clavicular head), coracobrachialis, biceps brachii.

Extension (of the shoulder)

Movement involving the posterior deltoid, latissimus dorsi, teres major, and triceps brachii (long head).

Abduction (of the shoulder)

Movement primarily executed by supraspinatus and deltoid (middle fibers).

Adduction (of the shoulder)

Movement primarily executed by pectoralis major, latissimus dorsi, and teres major.

External Rotation (of the shoulder)

Movement primarily executed by infraspinatus, teres minor, and posterior deltoid.

Internal Rotation (of the shoulder)

Movement primarily executed by subscapularis, teres major, pectoralis major, latissimus dorsi, and anterior deltoid.

Scapulohumeral Rhythm

The coordinated movement where for every 2° of humeral movement, the scapula moves 1° to maintain stability and function.

Superior Glenohumeral Ligament (SGHL)

Prevents inferior displacement of the humeral head.

Middle Glenohumeral Ligament (MGHL)

Resists anterior translation of the humeral head at mid-range abduction.

Inferior Glenohumeral Ligament (IGHL)

Supports the joint at high abduction angles, resisting anterior and posterior dislocations.

Coracohumeral Ligament (CHL)

Prevents excessive inferior displacement of the humeral head and limits external rotation at lower degrees of abduction.

Coracoacromial Ligament (CAL)

Forms the coracoacromial arch, preventing superior displacement of the humeral head; involved in shoulder impingement syndrome when inflamed.

Acromioclavicular Ligaments (ACL)

Reinforces the acromioclavicular joint to prevent excessive movement.

Coracoclavicular Ligaments (CCL)

Provide stability to the clavicle; includes the trapezoid (resists lateral displacement) and conoid ligament (prevents excessive superior movement).

Transverse Humeral Ligament

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

Shoulder Dislocations

Typically occur anteriorly, with the inferior GHL being 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 cause AC joint separation.