Shoulder Joint
(Glenohumeral Joint)
Definition: Joint between the Head of Humerus and Glenoid Cavity of scapula.
➜ Type: Synovial (Ball-and-Socket).
➜ Feature: Most movable joint in body = Least Stable (Most common to dislocate).
➜ Feature: Most movable joint in body = Least Stable (Most common to dislocate).
Articular Surfaces of Shoulder Joint
Articular Surfaces
1. Head of Humerus: Large and round.
2. Glenoid Cavity: Shallow.
➜ Glenoid Labrum: Fibrocartilaginous ring that deepens the cavity slightly.
2. Glenoid Cavity: Shallow.
➜ Glenoid Labrum: Fibrocartilaginous ring that deepens the cavity slightly.
Ligaments
1. Capsular Ligament
Thin and loose to allow movement.
➜ Medial: Margins of glenoid cavity (beyond labrum) + Supraglenoid tubercle (enclosing Long head of Biceps).
➜ Lateral: Anatomical neck (except inferiorly ➔ extends to Surgical Neck).
➜ Apertures: For Biceps tendon, Subscapular bursa, Infraspinatus bursa.
➜ Lateral: Anatomical neck (except inferiorly ➔ extends to Surgical Neck).
➜ Apertures: For Biceps tendon, Subscapular bursa, Infraspinatus bursa.
⚠️ Important: A portion of the epiphyseal line is intracapsular. Thus, Septic Arthritis may occur following metaphyseal osteomyelitis.
2. Accessory Ligaments
A. Glenohumeral (Sup/Mid/Inf): Anterior thickenings.
*Defect exists between Superior & Middle ligaments (site for Ant. Dislocation).
B. Coracohumeral: Coracoid ➔ Greater Tubercle.
C. Transverse Humeral: Bridges bicipital groove ➔ converts to canal.
D. Coracoacromial: Between Coracoid & Acromion.
Interior of the shoulder joint exposed from behind
to show the glenohumeral ligaments
B. Coracohumeral: Coracoid ➔ Greater Tubercle.
C. Transverse Humeral: Bridges bicipital groove ➔ converts to canal.
D. Coracoacromial: Between Coracoid & Acromion.
Coracoacromial, coracohumeral, and transverse
humeral ligaments as seen from the anterior aspect.
Coracoacromial Arch
(Coracoid + Acromion + CA Ligament)
Forms a Secondary Socket preventing superior displacement of the humerus.
(Coracoid + Acromion + CA Ligament)
Forms a Secondary Socket preventing superior displacement of the humerus.
Bursae
Subacromial/subdeltoid bursa
1. Subscapular: Communicates with joint cavity.
2. Subacromial (Subdeltoid): Largest bursa. Lies below Coracoacromial arch. Facilitates Supraspinatus movement.
3. Infraspinatus: May communicate with joint.
*NB: Opening a bursa may mean entering the joint cavity.
2. Subacromial (Subdeltoid): Largest bursa. Lies below Coracoacromial arch. Facilitates Supraspinatus movement.
3. Infraspinatus: May communicate with joint.
*NB: Opening a bursa may mean entering the joint cavity.
Relations
Important Relations
Relations of the Shoulder Joint
Superior: CA Arch, Subacromial bursa, Supraspinatus, Deltoid.
Inferior: Long head Triceps, Axillary Nerve, Post. Circumflex vessels.
Anterior: Subscapularis, Coracobrachialis, Short head Biceps, Deltoid.
Posterior: Infraspinatus, Teres Minor, Deltoid.
Blood & Nerve Supply
Arteries: Ant/Post Circumflex Humeral, Suprascapular, Subscapular.
Nerves: Axillary, Suprascapular, Musculocutaneous.
Nerves: Axillary, Suprascapular, Musculocutaneous.
Stability Factors
1. Rotator Cuff (SITS): Tone pulls head medially. (See diagram)
2. Coracoacromial Arch: Prevents upward dislocation.
3. Long Head of Biceps: Intracapsular tendon prevents upward displacement.
4. Glenoid Labrum: Deepens socket.
2. Coracoacromial Arch: Prevents upward dislocation.
3. Long Head of Biceps: Intracapsular tendon prevents upward displacement.
4. Glenoid Labrum: Deepens socket.
Action of the rotator cuff muscles: A, they grasp and pull the relatively large head of the humerus medially to hold
it against the smaller and shallow glenoid cavity; B, combined function of the rotator cuff muscles and deltoid
Movements
Movements of the shoulder joint
Range of Motion (ROM)
Flexion: 90°
Extension: 45°
Abduction: 180°
Adduction: 45°
Medial Rot: 55°
Lateral Rot: 45°
| Movement | Main Muscle (Prime Mover) |
|---|---|
| Flexion | Pect Major (clavicular), Deltoid (ant), Biceps (short), Coracobrachialis |
| Extension | Deltoid (post), Lat Dorsi, Teres Major |
| Abduction | Deltoid (lat), Supraspinatus, Serratus Ant, Trapezius |
| Adduction | Pect Major, Lat Dorsi, Teres Major |
| Med. Rotation | Subscapularis, Pect Major, Lat Dorsi |
| Lat. Rotation | Infraspinatus, Teres Minor, Deltoid (post) |
Mechanism of Abduction (180°)
0° - 90°: Glenohumeral Joint.
90° - 120°: Requires Lateral Rotation of Humerus (to clear acromion).
120° - 180°: Requires Scapular Rotation (Ratio 2:1).
*SC & AC joints move maximally during early & terminal stages respectively.
Clinical Anatomy
1. Dislocation:
Most common: Inferior (unsupported).
Risk: Injury to Axillary Nerve.
Naming: "Anterior" or "Posterior" based on where the head descends relative to glenoid.
2. Frozen Shoulder: (Adhesive Capsulitis)
Pain + Uniform limitation of all movements. Common in 40-60 yrs. Due to capsule shrinkage.
3. Rotator Cuff Disorders:
Common in throwing sports.
Painful Arc Syndrome: Pain between 60°-120° abduction (impingement).
Dawbarn's Sign: Pain elicited by pressure on deltoid (adducted arm) disappears when arm is abducted (bursa slips under acromion).
📚Ref: Vishram Singh - Upper Limb and Thorax
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