Anterior Shoulder Instability

The glenohumeral joint is the most commonly dislocated major joint, with an incidence of 24 per 100,000 per year. Anterior dislocations make up 95% of the total and posterior dislocations 2-4%. The peak is in males aged 15-25, and contact sports are overrepresented.

Mechanism. A force applied to the abducted, externally rotated arm, a direct blow to the posterior shoulder, or a fall on the outstretched hand. In sport the injury comes from tackling and overhead throwing. In the hyperlax shoulder the dislocation may be atraumatic.

Recurrence. Age at first dislocation is the strongest predictor. Under 20 years the recurrence rate is 67%; between 20 and 40 it is 30-40%; over 40 it falls to 10-15%, though the older patient carries a higher risk of rotator cuff tear. Young athletes in contact sports have the highest recurrence after conservative treatment, and young age with contact sport indicates early surgical consideration.

Static restraints. The glenohumeral ligaments are the primary static stabilisers. The inferior glenohumeral ligament (IGHL) is the most important: its anterior band resists anterior translation with the arm in abduction and external rotation. The middle glenohumeral ligament has variable anatomy and resists anterior translation in the mid-range, and the superior glenohumeral ligament resists inferior translation. The labrum deepens the glenoid by 50% and is the attachment for the ligaments.

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Dynamic restraints. The rotator cuff compresses the humeral head into the glenoid (concavity-compression), and subscapularis is the most important dynamic anterior stabiliser. The long head of biceps is a secondary restraint, and the periscapular muscles maintain the position of the glenoid.

The lesions. The key pathological lesions of anterior instability are:

• Bankart lesion: anteroinferior labral tear with avulsion of the IGHL, present in over 90%
• Bony Bankart: glenoid rim fracture with labral avulsion
• Hill-Sachs lesion: posterolateral humeral head compression fracture, present in 65-70% of first dislocations
• HAGL: humeral avulsion of the glenohumeral ligaments, less common
• ALPSA: anterior labroligamentous periosteal sleeve avulsion, with the labrum displaced medially

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History. Establish the mechanism (an abduction-external rotation position or a direct blow), whether the shoulder reduced spontaneously or needed reduction, the number of dislocations and their pattern, the level of sport (contact, overhead, competitive), and the age at first dislocation, which predicts recurrence.

Examination. The apprehension-relocation test is the most specific clinical test for anterior instability. With the patient supine, abduct the arm to 90° and externally rotate: the test is positive when the patient is apprehensive, not merely in pain. Then apply a posterior force to the humeral head; relief of the apprehension is a positive relocation test. Complete the examination with:

• Anterior load and shift, which grades translation
• Sulcus sign for inferior laxity, positive if greater than 2cm
• Beighton score for generalised laxity

The acute dislocation. The arm is held in external rotation and abduction, the deltoid contour is lost, and the humeral head is palpable anteriorly. After reduction, assess for neurovascular injury (especially the axillary nerve), rotator cuff integrity in patients over 40, and range of motion.

The older patient. In patients over about 40, a dislocation is more likely to combine dislocation, rotator cuff tear and neurological (axillary nerve or brachial plexus) injury, the so-called "terrible triad" of the shoulder. Persistent weakness after reduction in an older patient should not be assumed to be nerve injury alone: actively exclude a rotator cuff tear with ultrasound or MRI as well.

Radiographs. The standard views, and what each one shows:

• True AP (Grashey view): glenohumeral alignment
• Axillary lateral: the relationship of the glenoid and humeral head; essential
• Scapular Y: confirms the direction of dislocation
• West Point view: the anteroinferior glenoid (Bankart)
• Stryker notch view: the Hill-Sachs lesion

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What the plain films tell you. A Hill-Sachs visible on the AP indicates a significant lesion, one that is engaged in external rotation, and glenoid loss visible on the AP suggests bone loss greater than 20%. Either finding prompts CT quantification.

CT with 3D reconstruction is the gold standard for quantifying bone loss and essential for surgical planning. Glenoid loss is measured by the best-fit circle method on the en face view, as described under Classification. The Hill-Sachs is measured for width, depth and location, and glenoid version is checked to ensure the glenoid is not retroverted.

MRI shows the soft-tissue lesions: the Bankart, ALPSA and HAGL lesions described above, GLAD (glenoid labrum articular disruption), and the rotator cuff, which matters especially in patients over 40. MR arthrography is superior for labral pathology.

The acute dislocation must be reduced before any instability work-up, and naming and contrasting the reduction manoeuvres, with the safe principles around them, is a clinical and OSCE favourite. Provide adequate analgesia first, either intravenous sedation and analgesia or intra-articular local anaesthetic, which is effective and avoids the risks of sedation. Document neurovascular status, the axillary nerve in particular, before and after, and obtain a post-reduction radiograph to confirm reduction and exclude an iatrogenic fracture.

The painful or unstable-feeling shoulder in a young patient has several mimics. The exam trap is labelling everything "anterior instability" without distinguishing the direction and the driver, traumatic structural against atraumatic or volitional.

Algorithm

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The first dislocation. After closed reduction under sedation, post-reduction radiographs and assessment of the axillary nerve, immobilise in a sling. MRI assesses the labrum and rotator cuff; CT with 3D reconstruction quantifies bone loss and is essential for surgical planning.

Conservative treatment. A sling for 3-6 weeks, then progressive range of motion with rotator cuff and periscapular strengthening. This may be appropriate for the patient over 40, the low-demand patient, the shoulder with no bone loss, and the non-contact athlete.

Early surgery. Consider it in the patient under 20, the contact athlete, the shoulder with significant bone loss and the in-season athlete. Stabilisation reduces recurrence from 67% to less than 10%.

Recurrent instability. Quantify the bone loss first: CT with 3D reconstruction, glenoid loss by the best-fit circle, and the Hill-Sachs classified on-track or off-track. The procedure then follows the bone loss and the risk profile. The table uses 15% and 25% as its working cut-offs; the reasoning behind them, the 13.5% threshold for function and the 20-25% threshold for redislocation, is set out under Classification.

Arthroscopic Bankart suits glenoid bone loss under 15% with an on-track Hill-Sachs, a first stabilisation attempt and non-contact sport. Remplissage may be added if the Hill-Sachs is borderline.

Latarjet is mandatory above 25% glenoid bone loss, where the alternative is an iliac crest bone graft (Bristow-Eden-Hybinette technique). It is also the procedure for 15-25% loss with an engaging Hill-Sachs, for contact sport with an ISIS greater than 6, and after a failed Bankart, and many dislocations are a further reason to consider it. Combining Latarjet with remplissage is rarely needed and is reserved for an off-track Hill-Sachs with glenoid loss.

Arthroscopic Bankart succeeds in 80-90% of appropriately selected patients. Recurrence is higher in young contact athletes and with bone loss or an engaging Hill-Sachs.

Latarjet gives 95-98% stability, with low recurrence even in high-risk groups, at the cost of some risk of osteoarthritis in the long term.

Prognosis. Older age, non-contact sport, minimal bone loss, a first stabilisation and compliant rehabilitation predict a good result. Age under 20, contact sport, significant bone loss, an engaging Hill-Sachs, hyperlaxity and failed previous surgery predict a poor one.

Global Epidemiology

• Glenohumeral dislocation is the most common large-joint dislocation; population incidence is reported around 23-24 per 100,000 person-years, with anterior dislocations making up roughly 95% of cases.
• Bimodal distribution: a large peak in young males (15-25 years, sport and high-energy trauma) and a smaller peak in older patients (often with concomitant rotator cuff tears or greater tuberosity fractures).
• Recurrence is driven overwhelmingly by age and bone loss, a pattern consistent across cohorts worldwide (Robinson, Edinburgh; Hovelius, Sweden).

Society Guidance Side by Side

Registry and Outcome Signals

• Large series and registry-type data consistently show Latarjet with lower recurrence than isolated Bankart, balanced against a higher-acuity complication profile (An et al. meta-analysis).
• Revision and complication tracking (e.g. coracoid graft non-union, hardware removal) is increasingly captured in national shoulder-instability and arthroplasty-adjacent datasets to benchmark Latarjet safety.

High- vs Limited-Resource Practice Variation

How to measure bone loss. No single method is universal. The best-fit circle on 3D CT is the most used, but linear, area and surface-based methods give different percentages for the same defect, and the subcritical zone increasingly prompts augmentation below the classic threshold.

Surgery after the first dislocation. Whether to stabilise every young first-time dislocator is debated. The Robinson and Hovelius data show high but not universal recurrence, so shared decision-making that weighs sport, age, bone loss and patient preference is favoured over a blanket policy.

Arthroscopic versus open Latarjet. The arthroscopic Latarjet offers lower morbidity in expert hands but has a steep learning curve and graft-positioning and hardware concerns. Open Latarjet remains the reference standard, and no high-level evidence proves one superior for stability.

Free bone block alternatives. Iliac crest autograft and distal tibial allograft (anatomic glenoid reconstruction) avoid the conjoint sling but lose its dynamic effect. Their role versus Latarjet, and bone-block versus screw-versus-suture fixation, is unsettled.