In a shoulder dislocation, there is separation of the humerus from the glenoid of the scapula at the glenohumeral joint. The shoulder is exceptionally manoeuvrable and sacrifices stability to enable an increase in function. Therefore, it is vulnerable to dislocation, and is the most commonly dislocated large joint. In fact approximately half of major joint dislocations seen in emergency departments are of the shoulder 1.
This article contains a general discussion on shoulder dislocation. For specific dislocation types please refer to the following articles:
A number of biomechanical forces can produce shoulder dislocation, including 1:
- forced extension, abduction and external rotation
- most common
- leads to anterior dislocation
- direct blow from behind
- leads to anterior dislocation
- forceful contraction of shoulder girdle muscles
- leads to posterior dislocation
- forced hyperabduction 4
- leads to inferior dislocation
Shoulder dislocations are usually divided according to the direction in which the humeral exits the joint:
In addition it is useful to also include a description of their time course:
X-rays (AP and lateral +/- axillary view) are sufficient in almost all cases to make the diagnosis, although CT and MR are often required to assess for the presence of subtle fractures of the glenoid rim or ligamentous / tendinous injuries respectively.
Anterior and inferior dislocations are usually simple diagnoses, with the humeral head and outline of the glenoid being incongruent.
Posterior dislocations can be difficult to identify on an AP view only (as may be obtained in the setting of secondary survey of a trauma) as the humeral head moves directly posteriorly and congruency may appear to be maintained (at least at first glance).
All dislocations should be easily identified on trans-scapular Y views. In an enlocated (normally aligned) joint, the humeral head will project centred over the centre of the Y formed by the coracoid, blade of the scapula and spine of the scapula.
In addition to reporting the presence of a dislocation a number of features and associated findings should be sought and commented upon:
- direction of dislocation
- associated fractures/injuries
It is also important to remember to scrutinise the ribs and portion of the lungs and mediastinum included in the film for unexpected findings. Think about the soft tissue structures that might be injured, particularly the neurovascular bundle with inferior dislocations.
Relocation is the initial treatment, and as a general rule the shorter the duration of dislocation the fewer complications (size of Hill-Sachs lesion; neurovascular compromise, etc). This is followed by a period of immobilisation, 3 weeks for younger patients (< 30 years old, who have a very high rate of recurrence) and 7-10 days in older patients. During this time gentle active motion should be carried out to preserve range of motion 4.
Early arthroscopy, labral repair and debridement may be of use, especially in young patients with anterior dislocation in which there is a high (up to 85%) rate of recurrence 3.
- shoulder pseudo subluxation: apparent inferior displacement of the humeral head from capsular distension secondary to a haemarthrosis or large effusion
- 1. Manaster BJ, Disler DG, May DA et-al. Musculoskeletal imaging, the requisites. Mosby Inc. (2002) ISBN:0323011896. Read it at Google Books - Find it at Amazon
- 2. Zlatkin MB. MRI of the shoulder. Lippincott Williams & Wilkins. (2003) ISBN:0781715903. Read it at Google Books - Find it at Amazon
- 3. Peterson L, Renström P. Sports injuries, their prevention and treatment. Informa HealthCare. (2001) ISBN:1853171190. Read it at Google Books - Find it at Amazon
- 4. Simon RR, Sherman SC, Koenigsknecht SJ. Emergency orthopedics, the extremities. McGraw-Hill Professional. (2007) ISBN:0071448314. Read it at Google Books - Find it at Amazon