Shoulder Instability

Abnormal translation of the humeral head on the glenoid that produces pain, apprehension, subluxation or dislocation. The shoulder has the greatest range of motion of any joint and relies on static stabilisers (labrum, capsule, ligaments, glenoid and humeral shape) and dynamic stabilisers (rotator cuff and scapular muscles).

• Types:
  • Traumatic anterior instability (about 90 to 95% of dislocations): a fall or blow with the arm abducted and externally rotated, with a labral tear from the anteroinferior glenoid (Bankart lesion) and often a humeral head impression fracture (Hill-Sachs lesion).
  • Posterior instability (2 to 5%): seizures, electric shock, falls on the forward flexed arm, and repetitive loading.
  • Multidirectional instability: generalised ligamentous laxity (Ehlers-Danlos, Marfan, benign joint hypermobility) with symptoms in more than one direction, in young adults, often bilateral.
  • Atraumatic (voluntary or muscle patterning) instability.
• Incidence of shoulder dislocation is about 23 per 100,000 per year, with a peak in males aged 15 to 30. Recurrence after a first traumatic dislocation is up to 70 to 90% in patients under 20 years, 40 to 60% at 20 to 40, and under 10 to 20% above 40 (but with a higher chance of cuff tear).

• Acute anterior dislocation: severe pain, the arm held in slight abduction and external rotation and supported by the other arm, a squared off shoulder contour (loss of the deltoid roundness with a prominent acromion), and an empty glenoid.
• Chronic or recurrent: pain and apprehension with abduction and external rotation, a feeling of the shoulder slipping or "going out" (a dead arm), clicking, and weakness.
• Examination: apprehension test (arm abducted to 90 degrees and externally rotated, with fear of dislocation), relief of apprehension with a posteriorly directed force on the humeral head (relocation test), anterior and posterior load and shift, sulcus sign (a dimple distal to the acromion with downward traction, which does not close in external rotation in multidirectional instability), hypermobility score (thumb to forearm, elbow and knee hyperextension, palms to floor), and posterior jerk and Kim tests for posterior instability.
• Always examine the axillary nerve (sensation over the lateral shoulder regimental patch, deltoid contraction), the brachial plexus and radial pulse before and after reduction.
• Differential diagnosis: rotator cuff tear, SLAP lesion, acromioclavicular injury, fracture of the proximal humerus or glenoid, scapular dyskinesis, cervical radiculopathy, thoracic outlet syndrome, and seizure related dislocation.
• Red flags: neurovascular deficit, open injury, locked dislocation, associated proximal humeral fracture, first dislocation in a patient over 40 (cuff tear risk), and seizure or electric shock (posterior).
• Complications: recurrent dislocation, axillary nerve injury (5 to 35%), rotator cuff tears (above 30% in over 40s), glenoid bone loss, post-traumatic arthritis and stiffness.

• X-rays before and after reduction (anteroposterior, scapular Y, axillary or Velpeau views) to confirm the direction and exclude fracture.
• MRI or MR arthrography for labral tears, cuff tears and capsular laxity. CT with 3D reconstruction for glenoid and humeral bone loss (suspected when there are repeated dislocations, a lower threshold of dislocation, or sports contact). Ultrasound for bedside assessment.
• Electromyography for persistent nerve deficit beyond 3 to 4 weeks. Screen for connective tissue disease in multidirectional instability.

• Acute reduction (as soon as possible, after X-ray unless clearly a recurrent dislocation in an experienced patient):
  • Analgesia and relaxation: intra articular lidocaine 1% 10 to 20 mL (with 5 to 10 minutes' wait) or IV morphine 2.5 to 5 mg titrated, or procedural sedation (midazolam 1 to 2 mg IV titrated with fentanyl 0.5 to 1 microgram/kg IV, or propofol 0.5 to 1 mg/kg IV) with monitoring.
  • Techniques: external rotation, scapular manipulation, traction countertraction, Milch and Stimson methods.
  • Recheck neurovascular status and obtain post-reduction X-ray.
• Immobilisation in a sling for comfort for 1 to 3 weeks (longer periods do not reduce recurrence), then early physiotherapy.
• Rehabilitation for 3 to 6 months: restore range, rotator cuff and scapular strengthening, proprioceptive training, and sport specific work. Return to non-contact sport at 6 to 12 weeks and to contact sport after 3 to 6 months, with full range and strength.
• Surgery:
  • First time traumatic dislocation in young active patients (under 25 to 30 years, contact athletes, overhead workers) with a Bankart lesion: arthroscopic stabilisation (labral repair with suture anchors), with a recurrence of about 10 to 20%.
  • Glenoid bone loss above 15 to 20% or an engaging Hill-Sachs lesion: bone block procedure (Latarjet coracoid transfer) with a recurrence of about 2 to 8%, or remplissage.
  • Recurrent dislocation, failure of 3 to 6 months of rehabilitation, or functional instability: surgical stabilisation.
  • Posterior instability: physiotherapy first, and posterior labral repair or bone block for failure.
  • Multidirectional instability: 6 to 12 months of structured physiotherapy (strengthening of the rotator cuff, deltoid and scapular stabilisers) in most patients, with capsular shift (plication) reserved for failure and good motivation.
  • Prophylaxis: cefazolin 2 g IV once (3 g if above 120 kg).
• Analgesia after reduction: paracetamol 1 g orally 6 hourly with ibuprofen 400 mg 8 hourly with food for 1 to 2 weeks, and codeine 30 mg orally 6 hourly (or tramadol 50 mg 6 hourly) for severe pain for a few days.
• Special groups:
  • Patients over 40: high risk of cuff tear and nerve injury, so arrange early review and MRI, and use short immobilisation.
  • Children and adolescents: higher recurrence, so refer early to paediatric orthopaedics, with consideration of early surgery for contact athletes.
  • Seizures and electrolyte disorders: treat the cause and refer for posterior instability.
  • Connective tissue disorders: rehabilitation first, and avoid excess capsular tightening.
  • Pregnancy: avoid sedation where possible, reduce under local anaesthetic, and use physiotherapy and paracetamol.
  • Renal impairment and gastrointestinal disease: avoid oral NSAIDs.
• Follow up: review at 1 week, 3 weeks and 6 weeks, then at 3 to 6 months. Refer urgently to orthopaedics for irreducible dislocation, neurovascular deficit, fracture dislocation, or first dislocation in a young athlete.