SN6
SHORT NOTE
5M
★ High-yield
Describe the rotator cuff with its muscles and functions. Add a note on supraspinatus tendinitis.
Definition
The rotator cuff is a musculotendinous sleeve formed by the tendons of four scapulohumeral muscles, which blend with the capsule of the shoulder joint and are its chief stabilisers.
The Four Muscles
| Muscle | Origin | Insertion | Nerve | Action |
|---|---|---|---|---|
| Supraspinatus | Supraspinous fossa | Upper facet, greater tubercle | Suprascapular | Initiates abduction (first 15°) |
| Infraspinatus | Infraspinous fossa | Middle facet, greater tubercle | Suprascapular | Lateral rotation |
| Teres minor | Upper lateral border of scapula | Lower facet, greater tubercle | Axillary | Lateral rotation |
| Subscapularis | Subscapular fossa | Lesser tubercle | Upper and lower subscapular | Medial rotation |
- Mnemonic — sits
- Three insert into the greater tubercle; only subscapularis into the lesser
- Three are lateral rotators; only subscapularis is a medial rotator
Functions
- Holds the head of the humerus against the glenoid cavity — the principal stabilising function
- Provides a fulcrum so that the deltoid can abduct rather than simply pull the humerus upward
- Depresses the humeral head during abduction, preventing impingement
- Produces rotation, and assists abduction
- The cuff is deficient inferiorly — the direct anatomical reason dislocation occurs downward
Supraspinatus and Impingement
- The critical zone — an area of relative avascularity about 1 cm proximal to the insertion, where degeneration and tears begin
- Calcific tendinitis may develop here and is intensely painful
Clinical Features and Tests
| Feature or test | Finding |
|---|---|
| Painful arc | Pain between 60° and 120° of abduction, relieved beyond it — the classical sign of supraspinatus lesion |
| Complete tear | Cannot initiate abduction; can hold the arm up if passively abducted past 15° (deltoid takes over) |
| Drop arm test | The arm falls suddenly when lowered from full abduction |
| Empty can (Jobe) test | Weakness of supraspinatus |
| Lift-off test | Tests subscapularis |
| External rotation lag | Tests infraspinatus |
Applied Aspects
- Rotator cuff disease is the commonest cause of shoulder pain in adults over 40
- Treatment — rest, NSAIDs, physiotherapy, subacromial corticosteroid injection; surgical repair or acromioplasty for a complete tear in an active patient
- Suprascapular nerve injury paralyses two of the four cuff muscles and weakens both abduction and lateral rotation
- Axillary nerve injury in shoulder dislocation paralyses deltoid and teres minor — test the regimental badge area for sensation
- Cuff-tear arthropathy — a long-standing massive tear allows the humeral head to migrate upward against the acromion, destroying the joint
All questions in Upper Limb
- Q1Describe the formation, parts and branches of the brachial plexus. Add a note on its injuries. ★
- Q2Describe the boundaries and contents of the axilla. Add a note on the axillary artery and the axillary lymph nodes. ★
- Q3Describe the shoulder joint under type, ligaments, movements and stability. Add a note on its dislocation. ★
- Q4Describe the boundaries and contents of the cubital fossa. Add a note on the compartments of the arm and the brachial artery. ★
- Q5Describe the small muscles of the hand with their nerve supply. Add a note on the fascial spaces and the palmar arches. ★
- SN1Write a short note on Erb–Duchenne palsy. ★
- SN2Describe the course of the radial nerve and the effects of its injury at different levels. ★
- SN3Describe the carpal tunnel with its contents. Discuss carpal tunnel syndrome. ★
- SN4Describe the course of the ulnar nerve and the features of its injury. Explain the ulnar paradox. ★
- SN5Describe the anatomical snuffbox with its boundaries and contents. Add a note on scaphoid fracture. ★
- SN6Describe the rotator cuff with its muscles and functions. Add a note on supraspinatus tendinitis. ★
- SN7Describe the cutaneous innervation and dermatomes of the upper limb.