Shoulder Joint Anatomy
Glenohumeral joint structure, stability mechanisms, and clinical relevance — the essential foundation for upper limb assessment and rehabilitation.
Overview
The glenohumeral joint (GHJ) is a ball-and-socket synovial joint formed by the articulation of the humeral head with the glenoid fossa of the scapula. It is the most mobile joint in the human body, sacrificing bony stability for range of movement — making it the most commonly dislocated joint.
Understanding shoulder anatomy is the clinical foundation for:
- Diagnosing rotator cuff tears, impingement syndromes and instability
- Interpreting special orthopaedic tests accurately
- Designing evidence-based rehabilitation programmes
- Communicating effectively with orthopaedic surgeons and radiologists
Bony Anatomy
Three bones form the shoulder complex:
/* SCAPULA key landmarks */ Glenoid fossa → articulates with humeral head Acromion → forms roof of subacromial space Coracoid process → attachment for coracoacromial ligament Spine of scapula → palpation landmark, separates supra/infra /* HUMERUS key landmarks */ Head → 2/3 sphere, 135° neck-shaft angle Greater tuberosity → supraspinatus, infraspinatus, teres minor Lesser tuberosity → subscapularis Bicipital groove → long head of biceps tendon
Rotator Cuff — SITS Muscles
The rotator cuff consists of four muscles that provide dynamic stability and fine-tune glenohumeral movement. Remember the acronym SITS:
| Muscle | Origin | Insertion | Action | Nerve |
|---|---|---|---|---|
| Supraspinatus | Supraspinous fossa | Greater tuberosity (superior facet) | Abduction (0–15°), humeral head depression | Suprascapular (C5, C6) |
| Infraspinatus | Infraspinous fossa | Greater tuberosity (middle facet) | External rotation, horizontal abduction | Suprascapular (C5, C6) |
| Teres Minor | Lateral border scapula | Greater tuberosity (inferior facet) | External rotation, adduction | Axillary (C5, C6) |
| Subscapularis | Subscapular fossa | Lesser tuberosity | Internal rotation, adduction, anterior stability | Upper/lower subscapular (C5–C7) |
Stability Mechanisms
Glenohumeral stability is provided by static and dynamic restraints working together:
STATIC STABILISERS Bony: glenoid labrum (deepens socket 50%) Capsuloligamentous: SGHL → restrains ER at 0° abduction MGHL → restrains anterior translation at 45° ABD IGHL → PRIMARY restraint at 90° ABD (anterior band) Negative intra-articular pressure DYNAMIC STABILISERS Rotator cuff → compressive coaptation Biceps LH → superior stability (controversial) Deltoid → force couple with rotator cuff Periscapular muscles → stable base for GHJ
Range of Motion — Normal Values
| Movement | Normal ROM | End Feel | Prime Mover |
|---|---|---|---|
| Flexion | 0–180° | Firm (capsuloligamentous) | Anterior deltoid, pectoralis major |
| Extension | 0–60° | Firm | Posterior deltoid, latissimus dorsi |
| Abduction | 0–180° | Firm / bone-to-bone | Deltoid (mid), supraspinatus |
| Adduction | 0–45° | Soft (tissue apposition) | Pectoralis major, latissimus dorsi |
| Int. Rotation | 0–70° | Firm | Subscapularis, pectoralis major |
| Ext. Rotation | 0–90° | Firm | Infraspinatus, teres minor |
✏️ Test Yourself — Shoulder Anatomy Quiz
1. Which rotator cuff muscle inserts into the lesser tuberosity of the humerus?
2. The subacromial space normally measures:
3. Which ligament is the primary restraint against anterior instability at 90° abduction?