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Dislocation, Shoulder
Updated: Feb 27, 2008
Introduction
Background
Shoulder dislocation is documented in Egyptian tomb murals as early as 3000 BC, with depiction of a manipulation for glenohumeral dislocation resembling the Kocher technique. Hippocrates detailed the oldest known reduction method still in use today and advocated treating chronic shoulder instability with cauterization of the deep tissues of the anterior shoulder. Historical techniques to reduce dislocated glenohumeral joints have been shown to be safe when applied correctly. Kocher's method as originally described in 1870 did not involve traction and fell into disfavor when complications occurred with the application of large forces. The majority of dislocations are anterior, but less frequently, posterior, inferior (luxatio erecta), superior, and intrathoracic dislocations are also possible.
Pathophysiology
The shoulder is the most frequently dislocated joint. It moves almost without restriction but pays the price of stability. The shoulder's integrity is maintained by the glenohumeral joint capsule, the cartilaginous glenoid labrum (which extends the shallow glenoid fossa), and muscles of the rotator cuff.
In a recent review, anterior dislocations occurred in up to 98% of cases. Anterior displacement of the humeral head is the most common dislocation seen by emergency physicians. Posterior displacement is the next most frequently occurring dislocation. Inferior (luxatio erecta), superior, and intrathoracic dislocations are rare and are usually associated with complications.
Y-view radiograph of the right shoulder shows anterior dislocation of the humeral head relative to the glenoid fossa.
Frequency
United States
Shoulder dislocations affect approximately 1.7% of the population and are most frequently secondary to trauma. The incidence of all traumatic shoulder dislocations has been estimated at 11.2 cases per 100,000 person-years, with a cumulative incidence rate of 0.7% for men and 0.3% for women up to age 70 years.
International
A Danish study estimated the incidence of shoulder dislocation at 17 cases per 100,000.1 In a random sample of people in Sweden, 1.7% reported a history of shoulder dislocation.2
A more recent Greek study examined the demographic data and recurrence rates of shoulder dislocations of 308 patients (170 men and 138 women).3 Subjects were observed for approximately 6 years. The most frequent mechanism of injury was falling, and 92% of reductions were in the ED. The overall recurrence rate in all ages was 50%, but rose to almost 89% in the 14-20 year age group.
Sex
Gender distribution is bimodal, with peak incidence in men aged 20-30 years (with a male-to-female ratio of 9:1) and in women aged 61-80 years (with a female-to-male ratio of 3:1).
Age
Shoulder dislocation occurs more frequently in adolescents than in younger children because the weaker epiphyseal growth plates in children tend to fracture before dislocation occurs.
In older adults, collagen fibers have fewer cross-links, making the joint capsule and supporting tendons and ligaments weaker and dislocation more likely.
Anterior dislocation is most commonly seen in those aged 18-25 years due to sporting injury. The second most common age group to sustain anterior dislocation is in elderly persons due to their susceptibility to falls.
Clinical
History
Patients generally complain of severe shoulder pain and an associated decreased range of motion of the affected extremity. Mechanisms of injury are usually traumatic but may vary. Mechanisms may include sports, assaults, falls, seizures, throwing an object, reaching to catch an object, forceful pulling on the arm, reaching for an object, turning over in bed, or combing hair. It is not unusual for patients to have a history of recurrent ED visits for the same complaint. Specific mechanisms or historical facts may be suggestive of certain types of dislocations, such as lightning injuries, electrical injuries, and seizure with posterior dislocations; throwing a ball or a punch or forceful pulling of the arm with an anterior dislocation; and axial loading of an extremely abducted arm with inferior dislocation.
Physical
- Anterior shoulder dislocation (95-98% of ED dislocations)
- Arm is held in slight abduction and external rotation.
- Shoulder is "squared off" (ie, boxlike) with loss of deltoid contour compared with contralateral side.
- Humeral head is palpable anteriorly (subcoracoid region, beneath the clavicle).
- Patient resists abduction and internal rotation and is unable to touch the opposite shoulder.
- Compare bilateral radial pulses to help rule out vascular injury.
- In all cases, evaluate the axillary nerve before and after reduction by testing both pinprick sensation in the "regimental badge" area of the deltoid and palpable contraction of the deltoid during attempted abduction. Evaluate sensory and motor function of the musculocutaneous and radial nerves.
- Posterior shoulder dislocation (3% of ED shoulder dislocations)
- Arm is held in adduction and internal rotation.
- Anterior shoulder is "squared off" and flat with prominent coracoid process. Shoulders may look identical in bilateral dislocation, making it a commonly missed injury.
- Posterior shoulder is full with humeral head palpable beneath the acromion process.
- Patient resists external rotation and abduction.
- Neurovascular deficits are infrequent.
- Inferior (luxatio erecta) shoulder dislocation (0.5% of ED dislocations)
- Arm is fully abducted with elbow commonly flexed on or behind head.
- Humeral head may be palpable on the lateral chest wall.
Causes
- Anterior shoulder dislocations usually result from abduction, extension, and external rotation, such as when preparing for a volleyball spike. Falls on an outstretched hand are a common cause in older adults. The humeral head is forced out of the glenohumeral joint, rupturing or detaching the anterior capsule from its attachment to the head of the humerus or from its insertion to the edge of the glenoid fossa. This occurs with or without lateral detachment.
- Posterior dislocations are caused by severe internal rotation and adduction. This type of dislocation usually occurs during a seizure, a fall on an outstretched arm, or electrocution. Occasionally, a severe direct blow may cause a posterior dislocation. Bilateral posterior dislocation is rare and almost always results from seizure activity. Misinterpretation of the radiograph appearance of a posterior dislocation may result in misdiagnosis as a soft tissue injury in up to 79% of cases.
- Rare, but serious, inferior dislocations (luxatio erecta) may be due to axial force applied to an arm raised overhead, such as when a motorcycle collision victim tumbles to the ground. More commonly, the shoulder is dislocated inferiorly by indirect forces hyperabducting the arm. The neck of the humerus is levered against the acromion and the inferior capsule tears as the humeral head is forced out inferiorly. Luxatio erecta almost always has an associated fracture or soft-tissue injury. One series found 80% of patients to have fracture of the greater tuberosity or tear of the rotator cuff. Neurologic compromise was found in 60% of patients, with the axillary nerve the most commonly injured nerve. Inferior dislocations have the highest incidence (3.3%) of vascular compromise.
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References
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Further Reading
Keywords
glenohumeral dislocation, Kocher technique, shoulder pain, anterior shoulder dislocation, posterior shoulder dislocation, inferior shoulder dislocation, luxatio erecta, volleyball spike, fall on an outstretched arm, electrocution, seizure activity, shoulder dislocations, dislocated shoulder
