Shoulder Dislocations & Rotator Cuff Injuries
Orthopaedics · Trauma · lean revision notes
Shoulder Dislocations & Rotator Cuff Injuries
The glenohumeral joint is the most mobile—and therefore the most commonly dislocated—joint in the body. This topic blends trauma, anatomy, neurology (axillary nerve), and image-based recognition (Hill-Sachs, Bankart, "light-bulb" sign), making it a perennial NEET PG favourite.
Why the shoulder dislocates so easily
The glenohumeral joint is a ball-and-socket joint where a large humeral head articulates with a shallow, flat glenoid (only ~25–30% of the head is covered). Stability is sacrificed for mobility and is maintained by:
- Static stabilisers — glenoid labrum (deepens socket ~50%), glenohumeral ligaments (superior, middle, inferior—the inferior GHL is the key anterior stabiliser in abduction-external rotation), joint capsule, negative intra-articular pressure.
- Dynamic stabilisers — the four rotator cuff muscles and the long head of biceps, which actively centre the head in the glenoid.
High-yield: The inferior glenohumeral ligament (IGHL) is the most important static stabiliser preventing anterior dislocation when the arm is abducted and externally rotated.
Rotator cuff anatomy (SITS)
| Muscle | Origin (scapula) | Insertion | Innervation | Main action |
|---|---|---|---|---|
| Supraspinatus | Supraspinous fossa | Greater tuberosity (sup. facet) | Suprascapular n. | Initiates abduction (0–15°) |
| Infraspinatus | Infraspinous fossa | Greater tuberosity (mid facet) | Suprascapular n. | External rotation |
| Teres minor | Lateral border | Greater tuberosity (inf. facet) | Axillary n. | External rotation |
| Subscapularis | Subscapular fossa | Lesser tuberosity | Upper & lower subscapular n. | Internal rotation |
Mnemonic: "SITS" muscles. The three "S/I/T" insert on the greater tuberosity; subscapularis is the odd one out inserting on the lesser tuberosity and is the only internal rotator of the cuff.
High-yield: Supraspinatus is the most commonly torn rotator cuff muscle and the most commonly affected in impingement. Teres minor is the only cuff muscle supplied by the axillary nerve (the rest of the cuff is suprascapular/subscapular).
Part A — Shoulder Dislocations
Classification by direction
| Type | Frequency | Mechanism | Arm position on presentation |
|---|---|---|---|
| Anterior | ~95–97% | Abduction + external rotation + extension (fall on outstretched/forced ER) | Slightly abducted, externally rotated; resists internal rotation |
| Posterior | ~2–4% | Forced internal rotation/adduction — electrocution, seizure, "3 E's" | Adducted, internally rotated, fixed; cannot externally rotate |
| Inferior (luxatio erecta) | <1% | Hyperabduction force | Arm locked overhead, elbow flexed |
High-yield mnemonic — posterior dislocation "3 E's": Epilepsy (seizure), Electrocution, Ethanol (extreme intoxication/trauma). Posterior dislocation is the most commonly missed dislocation on a single AP film.
Anterior dislocation — sub-types
The humeral head most often comes to lie antero-inferiorly:
- Subcoracoid (commonest) → Subglenoid → Subclavicular → Intrathoracic (rare).
Clinical features
Anterior: loss of normal rounded deltoid contour → flattening, with a prominent acromion ("squaring of the shoulder"); the head may be palpable anteriorly; arm held in slight abduction & ER; all movements painful, especially internal rotation/adduction.
Posterior: arm locked in internal rotation; loss of external rotation is the hallmark; anterior shoulder appears flat, coracoid prominent.
Nerve & vessel injuries
High-yield: The axillary nerve is the most commonly injured nerve in anterior shoulder dislocation. Test it before and after reduction.
- Axillary nerve → tests: sensation over the regimental badge / lateral deltoid area (most reliable early sign as deltoid power is hard to assess acutely) and deltoid + teres minor function.
- Musculocutaneous, radial, median, ulnar and the posterior cord/brachial plexus may also be injured.
- Axillary artery injury — rare but feared, especially in elderly with atherosclerosis or in luxatio erecta.
Associated bony/soft-tissue lesions (classic image questions)
| Lesion | What it is | Associated with |
|---|---|---|
| Bankart lesion | Avulsion of the antero-inferior labrum (± glenoid rim = bony Bankart) | Anterior dislocation; main cause of recurrence |
| Hill-Sachs lesion | Compression fracture of the postero-lateral humeral head | Anterior dislocation |
| Reverse Hill-Sachs (McLaughlin) | Impaction of antero-medial humeral head | Posterior dislocation |
| Reverse Bankart | Posterior labral tear | Posterior dislocation |
| Greater tuberosity # | Avulsion fracture | Anterior dislocation in older patients |
| HAGL lesion | Humeral Avulsion of GH Ligament | Anterior instability |
High-yield: Bankart = cause of recurrence; Hill-Sachs = consequence (footprint) of the dislocation. In a young patient (<20 yrs) a first-time anterior dislocation has a very high recurrence rate (up to 80–90%) because of labral (Bankart) detachment.
Investigation of choice
Radiographs first — minimum two views:
- AP view of the shoulder
- Axillary (axillary lateral) or scapular-Y (trans-scapular) view — essential to confirm direction; an AP alone misses posterior dislocation.
Posterior dislocation radiographic signs:
- "Light-bulb" sign — head fixed in internal rotation looks symmetrical/round.
- "Rim sign" — widened (>6 mm) glenohumeral space.
- "Trough line" sign — reverse Hill-Sachs sclerotic line.
MRI / MR arthrography — investigation of choice for labral (Bankart) and cuff soft-tissue lesions, used pre-operatively in recurrent instability. CT best delineates bony Bankart and glenoid bone loss / engaging Hill-Sachs (relevant for surgical decision-making).
Management — reduction techniques
Stepwise approach: Confirm neurovascular status → adequate analgesia/sedation → closed reduction → re-check neurovascular status → post-reduction radiograph → immobilise → rehabilitate.
Closed reduction methods for anterior dislocation:
- Kocher's manoeuvre — Traction → External rotation → Adduction → Internal rotation (classic eponym; risk of humeral neck #, use gently).
- Hippocratic method — traction with counter-traction (heel in axilla — historical).
- Stimson (gravity) technique — prone, weight hanging from arm; gentle.
- Milch / Spaso / scapular manipulation — modern, low-force, less complication.
Immobilisation: sling for ~1–3 weeks (younger patients shorter, to avoid stiffness), then progressive rehab. There is evidence that immobilisation in external rotation may better reduce recurrence by reapproximating the Bankart lesion (less commonly practised).
Surgery:
- Recurrent anterior instability → Bankart repair (arthroscopic labral reattachment).
- Significant glenoid bone loss (>20–25%) → Latarjet procedure (coracoid transfer to glenoid).
- Engaging Hill-Sachs → Remplissage (infraspinatus tenodesis filling the defect).
High-yield: A first-time dislocation in a young athlete with a Bankart lesion may be offered early arthroscopic stabilisation because of very high recurrence; an elderly patient more often has a rotator cuff tear / greater tuberosity fracture rather than recurrent instability—always assess the cuff in the >40 yr group.
Complications
- Recurrent dislocation/instability (commonest, esp. young).
- Axillary nerve palsy (deltoid wasting, loss of abduction).
- Rotator cuff tear (esp. >40 yrs).
- Greater tuberosity / glenoid rim fractures.
- Vascular injury (axillary artery).
- Adhesive capsulitis / stiffness from prolonged immobilisation.
- Bankart & Hill-Sachs lesions → instability.
Part B — Rotator Cuff Disorders
A spectrum from impingement → tendinopathy → partial tear → full-thickness tear → cuff arthropathy.
Subacromial impingement
The supraspinatus tendon and subacromial bursa are compressed beneath the coraco-acromial arch (acromion, coraco-acromial ligament, AC joint) during abduction.
Neer classification of acromial morphology (risk factor for impingement):
- Type I — flat
- Type II — curved
- Type III — hooked (highest risk of cuff tear)
Clinical features
- Pain on overhead activity, night pain (lying on the shoulder).
- Painful arc — pain between 60°–120° of abduction (subacromial impingement). Pain at the very top (>170°/terminal) suggests AC joint pathology.
- Weakness of abduction/external rotation in tears.
Provocative / special tests
| Test | How | Tests |
|---|---|---|
| Neer's impingement | Passive forward flexion with arm internally rotated | Subacromial impingement |
| Hawkins-Kennedy | Flex shoulder & elbow 90°, internally rotate | Subacromial impingement |
| Jobe's (empty can) | Abduct 90° in scapular plane, thumb down, resist | Supraspinatus |
| Drop-arm test | Lower abducted arm slowly; sudden drop = positive | Supraspinatus (full-thickness tear) |
| External rotation lag / Infraspinatus | Resisted ER, arm at side | Infraspinatus |
| Lift-off (Gerber) / Belly-press | Hand behind back, push off / press belly | Subscapularis |
High-yield: A positive drop-arm test indicates a full-thickness supraspinatus tear. Jobe's (empty can) is the classic supraspinatus test; lift-off is the classic subscapularis test.
Diagnosis & investigation of choice
- Radiographs — may show high-riding humeral head (proximal migration → reduced acromiohumeral distance <7 mm suggests large/chronic tear), acromial spurs, sclerosis, cuff arthropathy.
- Ultrasound — operator-dependent, good for dynamic assessment, cheap, can detect full-thickness tears.
- MRI — investigation of CHOICE for the rotator cuff: characterises partial vs full-thickness tears, tendon retraction, muscle fatty atrophy (Goutallier grade) which predicts repairability.
High-yield: MRI is the investigation of choice for diagnosing a full-thickness rotator cuff tear; MR arthrography is best for partial-thickness/articular-side tears and labral pathology.
Management — drug & procedure of choice
Stepwise: Activity modification + NSAIDs (paracetamol/ibuprofen) → physiotherapy (cuff & scapular strengthening) → subacromial corticosteroid injection → surgery if refractory or large tear.
- Conservative is first-line for impingement and small/degenerate tears in older, low-demand patients: analgesics, physiotherapy, subacromial steroid injection (limit repeated injections—tendon weakening risk).
- Surgery:
- Subacromial decompression / acromioplasty for impingement.
- Arthroscopic cuff repair for symptomatic full-thickness tears, especially acute traumatic tears in younger/active patients (repair early).
- Tendon transfer (e.g., latissimus dorsi) or superior capsular reconstruction for irreparable tears.
- Reverse total shoulder arthroplasty for cuff-tear arthropathy (relies on deltoid; the prosthesis reverses the ball-socket geometry).
High-yield: Reverse shoulder arthroplasty is the procedure of choice for rotator cuff arthropathy because it shifts the joint's fulcrum and lets the deltoid power elevation when the cuff is deficient.
Complications of cuff disease
- Progression to massive/irreparable tear.
- Rotator cuff (Milwaukee shoulder) arthropathy with superior migration.
- Stiffness / adhesive capsulitis.
- Persistent weakness and disability.
Key differentials
- Adhesive capsulitis (frozen shoulder) — global loss of passive ROM (esp. external rotation), associated with diabetes; cuff tests not selectively weak.
- Calcific tendinitis — acute severe pain, calcium deposit in supraspinatus on X-ray.
- AC joint pathology — pain at terminal abduction, positive cross-body adduction (scarf) test.
- Biceps tendinopathy/SLAP tear — anterior pain, positive Speed's/O'Brien's test.
- Cervical radiculopathy (C5/C6) — referred shoulder pain with neck movement; check Spurling's.
- Septic arthritis / referred (cardiac, diaphragmatic) pain — always consider in atypical presentation.
High-yield: Adhesive capsulitis loses PASSIVE external rotation, distinguishing it from a cuff tear (where passive ROM is preserved but active power is lost). Strong association with diabetes mellitus and thyroid disease.
Recently asked / exam angle
- Image-based: Identify the light-bulb sign (posterior dislocation), squaring of shoulder (anterior), Hill-Sachs/Bankart on MRI/CT.
- "Patient post-seizure with arm fixed in internal rotation, cannot externally rotate" → posterior dislocation → order axillary/scapular-Y view.
- "Nerve most commonly injured in anterior shoulder dislocation" → Axillary nerve (regimental badge sensation loss).
- "Most commonly torn rotator cuff muscle" → Supraspinatus.
- "Investigation of choice for full-thickness cuff tear" → MRI.
- "Test for supraspinatus / subscapularis" → Empty can (Jobe) / Lift-off.
- "Cause of recurrent anterior dislocation" → Bankart lesion.
- "Procedure for glenoid bone loss / cuff arthropathy" → Latarjet / Reverse shoulder arthroplasty.
- "Painful arc 60–120°" → subacromial impingement.
Rapid revision
- Glenohumeral joint = most commonly dislocated; anterior (~95%) >> posterior > inferior.
- Posterior dislocation = 3 E's (Epilepsy, Electrocution, Ethanol); look for the light-bulb sign and order an axillary view.
- Axillary nerve = commonest nerve injured in anterior dislocation → test regimental badge sensation pre- and post-reduction.
- Bankart = antero-inferior labral avulsion → recurrence; Hill-Sachs = postero-lateral humeral head impaction.
- Reverse Hill-Sachs (McLaughlin) = posterior dislocation finding.
- Reduction: Kocher's (traction–ER–adduction–IR), Stimson, scapular manipulation; always re-image and re-examine nerves.
- Young first-time dislocators have very high recurrence → consider early arthroscopic Bankart repair; >20% glenoid bone loss → Latarjet.
- Rotator cuff = SITS; supraspinatus most commonly torn; subscapularis = only internal rotator, inserts on lesser tuberosity.
- Painful arc 60–120° = impingement; pain at terminal abduction = AC joint.
- Drop-arm + = full-thickness supraspinatus tear; Jobe (empty can) = supraspinatus; Lift-off = subscapularis.
- MRI = investigation of choice for cuff tears; MR arthrography for labral/partial tears; CT for bony glenoid loss.
- Reverse total shoulder arthroplasty = treatment of choice for cuff-tear arthropathy; adhesive capsulitis loses passive ER and is linked to diabetes.