Lucan · Conditions

Shoulder dislocation

Australian guidance: HealthPathways WA — Shoulder Dislocation / Orthopaedic Referral + EMST (RACS) reduction and analgesia principles + RACGP musculoskeletal clinical guidance

1. Definition and epidemiology

Shoulder (glenohumeral) dislocation is complete loss of contact between the humeral head and the glenoid fossa, distinct from subluxation, in which some articular contact is preserved. The glenohumeral joint is the most frequently dislocated major joint in the body, a direct consequence of the trade-off between mobility and stability built into its anatomy: the glenoid fossa is shallow and only articulates with roughly a quarter of the humeral head's surface at any one time, so the enormous range of shoulder movement is bought at the cost of relying heavily on soft-tissue restraints, the glenoid labrum, the glenohumeral ligament-capsule complex, and the dynamic stabilising action of rotator cuff, rather than bony congruity, to keep the joint located. Anterior dislocation accounts for roughly 95 to 97% of all glenohumeral dislocations, reflecting the mechanics of the joint's weakest point (the anteroinferior capsule), while posterior dislocation makes up only 2 to 4% and inferior (luxatio erecta) dislocation is rare. Incidence follows a bimodal pattern: a peak in young men in their teens and twenties from high-energy sporting and contact trauma, and a second peak in older adults, particularly women, from low-energy falls onto an outstretched or externally rotated arm, often in the setting of osteoporotic bone.

In the Australian context, anterior dislocation is heavily represented among presentations from rugby league, rugby union, Australian rules football, and netball, sports in which a tackle or fall with the arm abducted and externally rotated is common; this sporting pattern reinforces why the typical patient is a young adult male, although the second, low-energy fall-related peak in older women is equally important not to overlook.

2. Pathophysiology

Anterior dislocation is typically produced by an indirect force applied through an abducted, extended, and externally rotated arm, the classic mechanism of a fall onto an outstretched hand, an arm tackle, or a forced external rotation injury during throwing or wrestling. This position places the anteroinferior capsule and glenohumeral ligaments under maximal tension and levers the humeral head forward and inferiorly out of the glenoid, most commonly coming to rest in a subcoracoid position. As the humeral head levers over the anteroinferior glenoid rim, two characteristic "kissing" lesions are produced together and are worth understanding as a pair rather than in isolation. A Bankart lesion is avulsion of the anteroinferior glenoid labrum, and typically the attached inferior glenohumeral ligament complex, from the glenoid rim; when a fragment of glenoid bone is avulsed with the labrum this is termed a bony Bankart lesion. This injury strips away both the labral "bumper" that deepens the socket and the ligamentous checkrein that resists anterior translation, and it is the principal anatomical lesion underlying recurrent anterior instability. A Hill-Sachs lesion is the reciprocal injury on the humeral side: a compression (impaction) fracture of the posterolateral humeral head where it forcefully strikes the anteroinferior glenoid rim during dislocation. A larger or deeper Hill-Sachs defect that catches, or "engages", on the glenoid rim during normal arm rotation is a recognised driver of ongoing instability and is one of the findings that pushes management towards surgical rather than conservative treatment.

Posterior dislocation follows a fundamentally different, and far more easily missed, mechanism. Rather than a single traumatic force acting on a relaxed shoulder, it is classically produced by a violent, symmetric contraction of the internal rotator muscle group (subscapularis, pectoralis major, latissimus dorsi, and teres major), which collectively overpowers the weaker external rotators (infraspinatus and teres minor) and drives the humeral head posteriorly out of the glenoid. The two classic precipitants tested repeatedly in Australian exams are a generalised tonic-clonic seizure and high-voltage electric shock or electrocution, both of which cause exactly this kind of forceful, symmetric muscular contraction; a direct blow to the front of the shoulder is a less common, more intuitive alternative mechanism. Bilateral posterior dislocation after a seizure is a specific, high-yield exam pattern precisely because the same generalised muscular contraction affects both shoulders simultaneously. The bony and labral injuries mirror the anterior pattern but on the opposite surfaces: a reverse Bankart lesion (posteroinferior labral tear) and a reverse Hill-Sachs lesion, an impaction fracture of the anteromedial humeral head against the posterior glenoid rim, visible on imaging as a "trough line".

A minority of dislocations, particularly in younger patients with generalised ligamentous laxity, occur with minimal or no trauma and reflect an underlying multidirectional instability rather than a discrete traumatic Bankart lesion; this atraumatic pattern is managed primarily with structured physiotherapy focused on dynamic rotator cuff and scapular stabiliser strengthening, with surgery reserved for those who fail an adequate rehabilitation trial.

3. Clinical presentation and diagnostic criteria

Anterior dislocation produces a readily recognisable appearance: the patient holds the arm slightly abducted and externally rotated, actively resists any attempt at movement, and shows a loss of the normal rounded deltoid contour, often described as a "squared-off" shoulder, with the acromion made prominent and a palpable fullness or mass anterior to it where the humeral head has come to lie, and a corresponding hollow felt posteriorly.

Posterior dislocation is far more subtle and is missed on initial assessment in a substantial proportion of cases, most classically in a post-ictal or intoxicated patient whose examination is limited or whose complaint of shoulder pain is attributed to the seizure itself rather than a structural injury. The arm is held adducted and internally rotated against the body, and the single most useful bedside sign is a marked, often near-complete, inability to externally rotate the shoulder. The anterior shoulder appears flattened with a prominent coracoid process, and posterior fullness, though present, is easily overlooked, particularly in a muscular or obese patient. Any patient presenting after a seizure or electrical injury with shoulder pain and restricted external rotation should be assumed to have a posterior dislocation until imaging proves otherwise.

Neurovascular assessment is mandatory before any reduction attempt and must be repeated and documented immediately afterwards, since manipulation itself can cause or worsen a nerve injury. The axillary nerve is the nerve most commonly injured in glenohumeral dislocation because it winds directly around the surgical neck of the humerus through the quadrangular space, immediately adjacent to the inferior capsule that is stretched or torn in anterior dislocation. Motor testing of deltoid contraction is often unreliable in the acute setting because pain and guarding limit active movement, so the primary bedside test is sensation over the "regimental badge" area, the skin overlying the lateral deltoid and proximal lateral upper arm; sensory loss here (a positive regimental badge sign) indicates a likely axillary nerve injury, most commonly a neurapraxia that recovers over weeks to months. Distal pulses and capillary refill should also be checked, since axillary artery injury is a rare but recognised complication, particularly in older patients with atherosclerotic vessels.

In the chronic or subacute setting after an anterior dislocation has resolved, a positive apprehension test, reproduction of a sense of impending instability when the shoulder is passively abducted and externally rotated, relieved by the relocation test (a posteriorly directed force over the humeral head), supports a diagnosis of ongoing anterior instability and is an examination sometimes used to guide referral decisions.

4. Investigations and AU-specific cutoffs

A standard trauma shoulder radiograph series comprises an anteroposterior (AP) view taken in the plane of the scapula (a "true AP" or Grashey view, which avoids overlap between the humeral head and glenoid), a scapular Y (lateral) view, and an axillary view. The axillary view is the single most useful view for confidently distinguishing anterior from posterior displacement and for identifying a bony Bankart fragment or a Hill-Sachs defect, but it requires abduction of the injured arm, which can be difficult to achieve in a patient in acute pain; a modified or Velpeau axillary view, taken with the arm resting in a sling, allows the same projection without active abduction. Posterior dislocation is the classic radiographic trap in this topic: a single AP view can look deceptively unremarkable because the displacement is predominantly anteroposterior and is poorly seen end-on, and up to half of posterior dislocations are missed at first presentation for exactly this reason. Subtle clues on the AP film include the "light bulb sign" (the humeral head appears symmetrically round because it is fixed in internal rotation), the "rim sign" (a widened glenohumeral joint space), and, when a reverse Hill-Sachs lesion is present, a "trough line" paralleling the medial cortex of the humeral head. A scapular Y or axillary view is required whenever posterior dislocation is suspected clinically or the AP view is equivocal.

CT is used where a plain film is equivocal, where a complex fracture-dislocation is suspected, or, in the non-acute setting, to quantify glenoid and humeral head bone loss before planning stabilisation surgery in a patient with recurrent instability. MRI, often as an MR arthrogram, is reserved for the non-acute setting to characterise labral (Bankart), capsular, and rotator cuff integrity; it is particularly useful in older patients, in whom a concurrent rotator cuff tear is a more likely associated injury than in the young.

Point-of-care ultrasound is increasingly used in some Australian emergency departments as a rapid bedside adjunct to confirm dislocation and, after reduction, successful relocation, without needing to move an acutely painful patient to the radiology department, although it does not replace plain radiography for characterising associated bony injury.

5. Management

Analgesia and, where required, procedural sedation precede any reduction attempt. Options used in Australian emergency departments include intra-articular local anaesthetic injection, intravenous procedural sedation (for example fentanyl with midazolam, or ketamine), and inhaled methoxyflurane, a rapid-onset, self-administered inhaled analgesic widely used by both St John WA and hospital emergency departments for exactly this kind of acute musculoskeletal pain. No single closed reduction technique is endorsed over the others in Australian guidance; commonly used methods include traction-countertraction, the external rotation (Hennepin) method, scapular manipulation, and the Stimson (gravity-assisted) technique, while Kocher's method is used less often because its rotational leverage component carries a higher risk of converting a simple dislocation into a fracture-dislocation. Whichever technique is chosen, reduction should be attempted slowly and with steadily increasing traction rather than sudden force, particularly in older patients with osteoporotic bone, and a displaced fracture (most importantly of the surgical neck) identified on the pre-reduction film generally prompts orthopaedic involvement before closed reduction is attempted, since manipulation risks worsening fracture displacement.

Post-reduction care begins with an immediate repeat neurovascular examination, followed by a post-reduction radiograph to confirm concentric relocation and to exclude an iatrogenic or previously occult fracture. The shoulder is then immobilised in a sling, traditionally in the adducted, internally rotated position, for roughly one to three weeks; some evidence suggests immobilisation in external rotation better approximates a Bankart lesion to the glenoid rim and may reduce recurrence, but this has not become standard Australian practice. Structured physiotherapy follows sling removal to restore range of motion and rotator cuff strength. Orthopaedic referral is recommended for every first-time dislocation, and is particularly important in young patients, given the high recurrence risk discussed below, and in anyone with a large Hill-Sachs defect, a bony Bankart fragment, or an associated fracture, since these findings increasingly prompt consideration of early arthroscopic stabilisation rather than the older approach of conservative management reserved for after multiple recurrences.

Reduction should be attempted as promptly as safely possible once adequate analgesia is achieved, since a longer interval between injury and reduction is associated with a more difficult reduction, greater muscle spasm, and an increased risk of neurovascular compromise; conversely, reduction should never be forced or rushed ahead of adequate analgesia and, where indicated, sedation.

6. Pharmacology and AU PBS notes

Simple analgesia (paracetamol and, where not contraindicated, an NSAID) covers ongoing post-reduction discomfort. Methoxyflurane (Penthrox, the "green whistle") is a distinctively Australian and New Zealand analgesic option, self-administered via a hand-held inhaler, with rapid onset and offset that makes it well suited to prehospital use by ambulance services and to brief, painful procedures such as closed reduction in the emergency department; its low-dose intermittent use for acute pain avoids the respiratory depression risk associated with opioid-based procedural sedation. Where procedural sedation is used instead, fentanyl (rapid onset, short acting) and midazolam, or ketamine as a single agent, are standard choices, with full airway and cardiorespiratory monitoring throughout, consistent with EMST procedural sedation principles. There is no PBS-listed pharmacotherapy directed at the joint injury itself; management is mechanical (reduction, immobilisation, rehabilitation, and surgery where indicated) rather than pharmacological beyond analgesia.

7. Complications and monitoring

Axillary nerve neurapraxia is the most common neurological complication and, while most cases recover spontaneously over weeks to months, sensory and motor function should be reassessed at follow-up; a persistent deficit at around three months warrants nerve conduction studies or electromyography and referral for consideration of surgical exploration. A greater tuberosity avulsion fracture accompanies a meaningful minority of anterior dislocations, particularly in older patients, and is clinically important because the greater tuberosity is the insertion footprint of supraspinatus, infraspinatus, and teres minor, so an associated rotator cuff tear should be actively considered, especially if weakness persists after the acute pain and guarding have settled. Recurrent instability is the dominant long-term complication, and age at the time of first dislocation is by far its strongest predictor: teenagers and young adults under roughly 20 to 25 years of age face recurrence rates commonly quoted in the order of 60 to 90%, driven by more elastic tissue that heals less robustly, higher-demand sporting activity, and often a larger initial Bankart injury, whereas patients over 40 have a substantially lower recurrence risk, often quoted under 10 to 20%, but a correspondingly higher chance of an associated rotator cuff tear. This steep age gradient is why a first-time dislocation in a young patient is increasingly referred early for consideration of arthroscopic stabilisation rather than managed with sling immobilisation alone. A missed or delayed-diagnosis posterior dislocation, the classic trap after seizure or electrocution, can progress to a chronic locked dislocation that is far harder to reduce closed and carries a substantially higher complication rate the longer treatment is delayed, reinforcing why restricted external rotation after a seizure should never be dismissed as simple post-ictal stiffness without imaging.

Post-traumatic stiffness and adhesive capsulitis are recognised complications, particularly in older patients managed with prolonged immobilisation, and are a further reason structured physiotherapy is started promptly once the sling is discontinued rather than being left to informal, unsupervised mobilisation.

Written for Australian practice and grounded in the guidance named above. Study material only — not medical advice. Always check against current guidelines.