Dislocated shoulder

X-ray at left shows anterior dislocation in a young man. X-ray at right shows the same shoulder after reduction and internal rotation, revealing a Bankart lesion and a Hill-Sachs lesion.

In over 95% of shoulder dislocations, the humerus is displaced anteriorly.[6] In most of those, the head of the humerus comes to rest under the coracoid process, referred to as sub-coracoid dislocation. Sub-glenoid, subclavicular, and, very rarely, intrathoracic or retroperitoneal dislocations may also occur.[7]

Anterior dislocations are usually caused by a direct blow to, or fall on, an outstretched arm. The person typically holds his/her arm externally rotated and slightly abducted.

A Hill–Sachs lesion is an impaction of the head of the humerus left by the glenoid rim during dislocation.[5] Hill-Sachs deformities occur in 35–40% of anterior dislocations. They can be seen on a front-facing X-ray when the arm is in internal rotation.[8] Bankart lesions are disruptions of the glenoid labrum with or without an avulsion of bone fragment.

Damage to the axillary artery[9] and axillary nerve (C5, C6) may result. The axillary nerve is injured in 37% making it the most commonly injured structure with this type of injury.[10] Other common, associated, nerve injuries include injury to the suprascapular nerve (29%) and the radial nerve (22%).[10] Axillary nerve damage results in a weakened or paralyzed deltoid muscle and as the deltoid atrophies unilaterally, the normal rounded contour of the shoulder is lost. A person with injury to the axillary nerve will have difficulty in abducting the arm from approximately 15° away from the body. The supraspinatus muscle initiates abduction from a fully adducted position.

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  An anterior dislocation of the shoulder
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  Anterior dislocation of the right shoulder. AP X ray
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  Anterior dislocation of the right shoulder. Y view X ray.

Lightbulb sign indicative of posterior shoulder dislocation shown on the left. On the right, the same shoulder after reduction.

Posterior dislocations are uncommon, and are typically due to the muscle contraction from electric shock or seizure.[5] They may be caused by strength imbalance of the rotator cuff muscles. People with dislocated shoulders typically present holding their arm internally rotated and adducted, and exhibiting flattening of the anterior shoulder with a prominent coracoid process.

Posterior dislocations may go unrecognized, especially in an elderly person[11] and in people who are in the state of unconscious trauma.[12] An average interval of 1 year was noted between injury and diagnosis in a series of 40 people.[13]

An inferior dislocation of the shoulder after an automobile accident. Note how the humerus is abducted. Also present is a fracture of the greater tuberosity.

Inferior dislocation is the least likely, occurring in less than 1%. This condition is also called luxatio erecta because the arm appears to be permanently held upward or behind the head.[14] It is caused by a hyper abduction of the arm that forces the humeral head against the acromion.[15] Such injuries have a high complication rate as many vascular, neurological, tendon, and ligament injuries are likely to occur from this mechanism of injury.

An example of a shoulder reduction technique, specifically the Cunningham technique

Shoulder reduction may be accomplished with a number of techniques including traction-countertraction, external rotation, scapular manipulation, Stimson technique, Cunningham technique, or Milch technique.[1][3] Pain can be managed during the procedures either by procedural sedation and analgesia or injected lidocaine into the shoulder joint.[16] Injecting lidocaine into the joint may be less expensive and faster.[4] If a shoulder cannot be relocated in the emergency room, relocation in the operating room may be required.[1] This situation occurs in about 7% of cases.[1]

[17]Stimson procedure is the least painful, widely used shoulder reduction technique. In this procedure a weight is attached to the wrist while the injured arm is hanging off an examination table for between 20 to 30 minutes. The arm is then slowly rotated until the shoulder is relocated. Sedatives are used in Stimson procedure and first time Stimson reduction for acute shoulder dislocation requires wearing arm slings for between 2 and 4 weeks.

There is no strong evidence of a difference in outcomes when the arm is immobilized in internal versus external rotation following an anterior shoulder dislocation.[18][19] A 2008 study of 300 people for almost six years found that conventional shoulder immobilisation in a sling offered no benefit.[20]

MRI of shoulder after dislocation with Hill-Sachs lesion and labral Bankart's lesion.

In young adults engaged in highly demanding activities shoulder surgery may be considered.[21] Arthroscopic surgery techniques may be used to repair the glenoidal labrum, capsular ligaments, biceps long head anchor or SLAP lesion or to tighten the shoulder capsule.[22]

Arthroscopic stabilization surgery has evolved from the Bankart repair, a time-honored surgical treatment for recurrent anterior instability of the shoulder.[23] However, the failure rate following Bankart repair has been shown to increase markedly in people with significant bone loss from the glenoid (socket).[24] In such cases, improved results have been reported with some form of bone augmentation of the glenoid such as the Latarjet operation.[25][26][27]

Although posterior dislocation is much less common, instability following it is no less challenging and, again, some form of bone augmentation may be required to control instability.[28] Damaged ligaments, including labral tears, occurring as a result of posterior dislocations may be treated arthroscopically.

There remains those situations characterized by multidirectional instability, which have failed to respond satisfactorily to rehabilitation, falling under the AMBRI classification previously noted. This is usually due to an overstretched and redundant capsule which no longer offers stability or support. Traditionally, this has responded well to a 'reefing' procedure known as an open inferior capsular shift.[29] More recently, the procedure has been carried out as an arthroscopic procedure, rather than open surgery, again with comparable results.[29] Most recently, the procedure has been carried out using radio frequency technology to shrink the redundant shoulder capsule (thermal capsular shrinkage);[30] while long-term results of this development are currently unproven, recent studies show thermal capsular shrinkage have higher failure rates with the highest number of cases of instability recurrence and re-operation.[27]