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Shoulder instability


Shoulder dislocation is a common orthopaedic injury that occurs via either a traumatic or atraumatic mechanism.  Traumatic dislocation, the subject of this chapter, is far more common and overwhelmingly occurs in the anteroinferior direction.

Structure and function

Shoulder dislocation results in primarily a soft tissue injury, although there can be associated fractures (e.g., humeral neck, greater tuberosity, glenoid rim) in the acute setting and erosive bone loss in the setting of chronic/recurrent instability.

The key soft-tissue anatomy includes the labral-ligamentous and capsular structures.  The inferior glenohumeral ligament (IGHL) is the primary restraint to translation of the humerus when the arm is in the vulnerable position of abduction (90?) and external rotation (90?).  In this position, the anterior band of the IGHL prevents anterior translation of the humeral head and the posterior band prevents posterior translation.  The labrum is a thickening of collagenous tissue that surrounds the glenoid, acting to deepen it and serve as an attachment site for important static (e.g., glenohumeral ligaments) and dynamic (e.g., long head biceps tendon) stabilizers.

The classic “Bankart lesion” which was first described in 1924, involves a tearing of the labrum from the 2 to 6 O’clock position with the attached anterior IGHL.  This lesion occurs in up to 90% of patients with traumatic anteroinferior instability (Bankart & Cantab 1924).  More recent evidence suggests that a stretching or redundancy of the anterior capsule of the shoulder joint also contributes to the pathology (Speer et al. 1994).

The physician must also be aware of a potential impression fracture in the posterosuperior head of the humerus that can occur with contact of the dislocated head and the anteroinferior glenoid rim.  This is termed the “Hill-Sach’s” lesion.  Erosive bone loss on the glenoid side is called the “bony Bankart.”


Traumatic anterior shoulder dislocation is primarily a disease of young and active persons.  It typically occurs during sporting events, but can also occur with high or low energy trauma.  The shoulder is the most commonly dislocated joint in the body.

The incidence of shoulder dislocation in the United States has been estimated as 25/100,000 person-years (Zacchilli & Owens 2010).  In Ontario, Canada the incidence was measured from hospital records over a 14 year period and found to be 23.1/100,000 person years. The incidence was, however, higher in males (34.2) than females (12.1), and highest in persons less than 20 years of age (45.3) compared to those between 20 and 40 years (21.2) and those over age 40 (19.9).

Little has been written about the economic impact of shoulder instability, however, the condition primarily affects a key workforce demographic – young males – and therefore the economic impact may be significant.


Clinical presentation

Acute shoulder dislocation typically occurs during athletic activity and is common in volleyball, basketball and hockey.  It may also occur as a result of a low energy fall or as part of a more serious pattern of injury in high-energy trauma.  The most common mechanism of injury is forced external rotation of the arm while it is in the vulnerable position of 90? abduction and 90? external rotation.

After injury, the patient typically holds the arm at the side and next to the body (internally rotated). The shoulder can often look “squared-off” (prominence of the acromion) and there may be a palpable or visible bulge anteriorly.  Specific attention should be paid to associated injuries.  The most common associated injuries include:

-       Neuropraxia of the axillary nerve (necessitating a comprehensive, well documented neurologic examination)

-       Fracture of the greater tuberosity or humeral neck (necessitating radiographs)

-       A rotator cuff tear (necessitating a close follow-up with attention paid towards cuff motion and strength)

These injuries become increasingly common with greater age.

In the context of high-energy mechanism of injury, a vascular injury must be ruled out, as must concomitant fractures in adjacent bones and chest wall trauma.

A history of seizure (e.g. from alcohol withdrawal, electrical shock) or violent trauma should also trigger suspicion for a posterior dislocation – see section “red flags” for further information.


Red flags

There are two pathologic conditions (“red flags”) that present alongside the more common traumatic anterior shoulder dislocation.

Some patients are pre-disposed to multi-directional instability.  Typically these patients have ligamentous laxity that may or may not be associated with an underlying cartilage abnormality such as Marfan’s or Ehler’s-Danlos syndrome.  With regards to multi-directional instability, the clinician should consider:



“Red Flag”

Physical examination

-       Positive “sulcus sign”
-       Positive tests for posterior instability/translation
-       Signs of generalized ligamentous laxity (knee hyperextension, elbow hyperextension, thumb to forearm & hyperextension of the 4th MCP past 90?)


-       Voluntary dislocation
-       Dislocation in the absence of a history of trauma

MDI is important to distinguish from traumatic anterior instability because the treatment is different.  In addition, if the clinician identifies a patient with an underlying responsible condition (e.g., connective tissue disorder), this should precipitate further work-up of other affected organ systems using a patient care team approach.

The second condition a clinician should hold suspicion for is a posterior dislocation.


“Red Flag”

Physical examination

-       A block to external rotation


-       Violent trauma
-       Seizure disorder, alcohol withdrawal, electrical shock

Finally, even some presentations of typical traumatic anterior shoulder dislocations may require extra care.  For instance, extensive bruising and swelling or pain seemingly out of proportion may signal a fracture-dislocation.  Furthermore, the clinician should be aware of incarcerated dislocations (typically subcoracoid) that may present with neurologic or vascular injury and constitute an emergency.  A careful and complete physical examination is paramount in all patients.

Differential diagnosis

The differential diagnosis for shoulder pain after trauma is wide and includes:

-       Rotator cuff tear

-       Fracture (tuberosity, neck of humerus, distal clavicle, scapula/acromion)

-       AC joint separation

-       Muscle strain/tear


Objective evidence

The workhorse investigation is the plain x-ray.  Typically three views are required – the AP, scapular lateral and axillary view.  The axillary view is key to differentiating an anterior from a posterior dislocation, although there are subtle findings on the other views.  Occasionally, a CT scan may be necessary – typically in the setting of an osteoporotic fracture of the proximal humerus in order to determine if the head is located within the glenohumeral joint.

Occasionally there are subtle findings on x-ray, the AP view in particular, that can trick an inexperienced physician.  A ‘high’ humeral head on the AP view is likely to represent a long-standing massive rotator cuff tear, where the deltoid muscle pulls the humerus proximally without the depressing effect of the rotator cuff.  A ‘low’ humeral head on the AP view may be a result of axillary neuropathy or pseudopalsy.

The best objective evidence in recurrent instability is to obtain an MRI or MR arthrogram to assess the status of the antero-inferior soft tissues (discussed above – labrum and IGHL).

Laboratory work is not usually indicated unless as a baseline when urgent surgery is considered.


Risk factors and prevention

Patients with the highest risk for this type of injury are young and male.  They often participate in collision/contact sports such as football and wrestling (Kerr et al. 2011).  Some evidence suggests patients with a natural degree of ligamentous laxity are at higher risk for dislocation (Chahal et al. 2010).  Other risk factors such as gender and age were previously discussed in the epidemiology section.

Primary prevention of shoulder dislocation is an area in need of further development.

Treatment options

Acute anterior shoulder dislocation is treated with a gentle closed reduction usually with either procedural sedation or intra-articular anesthesia.  Numerous methods have been described, and the evidence supporting the efficacy of one method over another is limited.  Described techniques include those with the patient prone or supine, and with or without the use of an assistant.  One of the most familiar techniques is the traction-countertraction technique, which requires an assistant.  A sheet is placed under the patient’s armpit to provide gentle countertraction by the assistant, while the physician pulls the arm in-line.

Failed closed reduction necessitates a step-wise treatment protocol that begins with repeated attempted closed reduction under general anesthesia.  Failing closed reduction, open reduction is performed.  In most instances if open reduction is performed, this is accompanied by a soft-tissue repair.  Incarcerated structures such as a fractured tuberosity or the long head biceps tendon may cause the irreducible dislocation.

Once a shoulder has been relocated successfully and confirmed by 3-views of the shoulder, treatment consists either of immobilization or surgical repair.  Immobilization is the most common form of treatment.  Typical protocols range between 1 and 3-4 weeks of immobilization followed by physical therapy.

The best current evidence suggests there is no difference in recurrence for immobilization between one and three weeks (Paterson et al.2010).  Although an initial study suggested reduced recurrence rates could be achieved by immobilization in external rotation (Itoi et al. 2007), the results have not been duplicated (Liavaag et al. 2011) and the practice has not become commonplace.  Typical immobilization is in a sling with the arm in internal rotation.

There are some advocates of primary surgical stabilization as the treatment of first-time dislocation, especially in high risk patients.  Randomized controlled trials support the use of primary surgical stabilization in young active patients to reduce the risk of repeat dislocation (Kirkley et al. 1999; Robinson et al. 2008), but it is unclear whether this has become common practice.


-       Outcome of primary surgery

-       Outcome of surgery for recurrent instability

-       Outcome of immobilization

There are numerous prognostic factors contributing to the expected outcome of a traumatic shoulder dislocation.  Younger age, high activity level and bony erosion are associated with rates of recurrence.  Conversely, older patients are thought to have a lower likelihood of recurrence.  Initial reports quoted the chance of recurrence in a person less than 20 years of age and treated with closed reduction and immobilization as 90%.  This data has been recently refuted with reported rates closer to 40-60% (Paterson et al. 2010) in this age group.  Nevertheless, age remains potentially the most important prognosticator.

Patients who undergo surgical stabilization for either first-time (less common) or recurrent instability (more common) can expect successful surgery 85-95% of the time.  There is some variation in success related to the number of previous dislocations, bone loss and the technique (open versus arthroscopic).  Post-surgical dislocation and/or revision are considered failures of primary stabilization.

The long-term natural history of recurrent instability is largely unknown.  Patients with persistently subluxed shoulders that are treated with neglect are very likely to rapidly progress to arthrosis.  Often times chondral damage is seen at surgery, but whether this damage or the effect of joint stiffness post-operatively leads to greater long-term arthrosis is unknown.  Older techniques of non-anatomic surgical repair for shoulder dislocations (e.g., Putti Platt procedure) have been abandoned because of the high rate of associated stiffness and eventual arthritis.

Holistic medicine

Traumatic instability leads to activity limitations and usually accompanies a feeling of ‘mistrust’ towards the shoulder.  These can have negative effects on the athletic patient.  In some cases patients can have limitations at work or home life, including those who dislocate in their sleep (although typically these patients have either multi-directional instability or significant bone loss).


Clinical Pearls:

  • A history of alcohol use or seizures should trigger concern for a posterior dislocation
  • Radiographs must always include orthogonal views (AP, axillary)
  • Document a suspected dislocated shoulder with a radiograph prior to reduction; this can help identify an undisplaced fracture potentially made worse by an aggressive reduction maneuver


  • Surgery for first time dislocation in a young person
  • The indications for arthroscopic versus open soft tissue repair
    • ·      Shoulder dislocation
    • ·      Bankart
    • Instability

Key terms


Skills relevant to traumatic shoulder instability, include:

  • ·      Radiograph interpretation
  • ·      Conscious sedation principles
  • ·      Closed reduction maneuvers for a dislocated shoulder (traction-countertraction, scapular slide, Stimson, Milch)


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