Shoulder Dislocation

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Introduction

Anterior-shoulder-dislocation

Shoulder dislocation (correctly termed a glenohumeral joint dislocation) involves separation of the humerus from the glenoid of the scapula at the glenohumeral joint. The shoulder is inherently unstable joint due to the shallow glenoid articulating with a small part of the humeral head.

• This type of dislocation represent 50 percent of all major joint dislocations being the most regularly dislocated joint in the body.
• The shoulder can dislocate in an anterior (95% of shoulder dislocations), posterior, inferior direction and completely or partially.
• Fibrous tissue joining the bones is often stretched or torn, complicating a dislocation.

Etiology

The shoulder joint dislocates more frequently than any other joint in the body. A dislocation can become worse by strained or torn fibrous tissue which connects the bones. The bones can only be pulled out of position by a powerful force, such as a blow to the shoulder. Extreme rotation can cause the humeral head to come out of the glenoid labrum. Contact sports injuries are a common cause a dislocated shoulder as are motor trauma and falls.Trauma from motor vehicle accidents and falls can lead to shoulder dislocation.

Epidemiology

Shoulder joint dislocations are the most common dislocations of all major joint dislocations. The dislocation may occur anteriorly, posteriorly, inferiorly, or anterior-superiorly. Shoulder dislocations can be Anterior and Posterior dislocations. However, Anterior dislocations are the most common. It represent 95% of shoulder dislocation.

Risk factors for re-dislocation:

• Prior dislocation with poor tissue healing or soft issue laxity
• Younger patients have a much higher frequency of re-dislocation as they are more active
• Patients with torn rotator cuffs or fracture of the glenoid have a higher incidence of re-dislocation. 

Mechanism of Injury / Pathological Process

Strong forces or extreme rotation can cause the humeral head to come out of the glenoid labrum. Contact sports injuries are a common cause a dislocated shoulder as are motor trauma and falls.

Post reduction, both Bankart and Hill-Sachs lesions

Anterior Shoulder Dislocation
An anterior dislocation is the most common dislocation and is caused by the arm being positioned in an excessive amount of abduction and external rotation. In this position, the inferior glenohumeral complex serves as the primary restraint to anterior glenohumeral translation. Due to a lack of ligamentous support and dynamic stabilization, the glenohumeral joint is most susceptible to dislocation in the 90° abduction and 90° external rotation.

Complications and associated injuries include:

• Shoulder instability from damage to the inferior glenohumeral ligament.
• Hill-Sachs defect
• Bankart lesion or other anterior glenolabral injuries
• Damaged axillary artery, or brachial plexus

Posterior Shoulder Dislocation (PSD)
Posterior dislocation is less common as it accounts for 3% of shoulder dislocations. Typically the humeral head is forced posteriorly in internal rotation while the arm is abducted. Causes include: Convulsive disorders (most common cause in adults, often bilateral); electrocution; road trauma.

Clinical Presentation

Anterior Dislocation (humeral head comes to lie anterior, medial and slightly inferior to its normal location and glenoid fossa).

Following an acute anterior glenohumeral dislocation:

• Arm held in an abducted and ER position
• Loss of normal contour of the deltoid and acromion prominent posteriorly and laterally
• Humeral head palpable anteriorly
• All movements limited and painful
• Palpable fullness below the coracoid process and towards the axilla
• Possible damage to rotator cuff musculature and bone.
• Vascular injuries may result from traction of the axillary blood vessels, resulting in a reduced pulse pressure or a transient coolness in the hands. 
• Peripheral nerve injuries are common due to traction if the brachial plexus.

PSD with-reverse-hill-sachs-and-reverse-bankart-lesions

Posterior Dislocation

With acute posterior glenohumeral dislocation:

• Arm is abducted and IR
• May or may not lose deltoid contour
• May notice posterior prominence head of humerus
• Tear of subscapularis muscle (weak or cannot internally rotate)
• Neurovascular compromise is rare, but posterior shoulder instability may result from associated glenolabral and capsular injuries.

Posterior dislocations are hard to reduce, attempts at closed reduction need be performed in consultation with a treating orthopaedic surgeon. If the shoulder dislocation was ≥3 weeks ago (common in feeble elderly patients) or if their is reverse Hill-Sachs defect involving >20% of the articular surface, then the closed reduction is contraindicated.

Diagnostic Procedures

X-ray are is often enough to make a diagnosis of shoulder dislocation, however CT and MR are often needed to assess for the presence of subtle fractures of the glenoid rim or ligamentous/tendinous injuries respectively.

Outcome Measures

• Disabilities of the arm, shoulder and hand (DASH)
• QuickDASH
• Shoulder Pain and Disability Index (SPADI)
• Numeric Pain Rating Scale (NPRS)

Management / Interventions

A dislocated shoulder needs prompt reduction. This is usually performed in the Emergency Department following sedation and appropriate analgesia. A number of techniques can be used to reduce the shoulder. See also Therapeutic Exercise for the Shoulder.

Anterior Dislocation
ASDs are usually treated with closed reduction and a period of immobilisation (e.g. 6 weeks), allowing for adequate capsular healing. For successful healing and eventual normal function a structured course of physical therapy is needed to reduce muscle wasting and maintain mobility. During immobilisation, isometric exercises for shoulder muscles are paramount. Surgical repair may be required for dislocation treat complications and associated injuries (see above).

Following traumatic ASD, there is great variability in the post-operative immobilisation period and at which stage each type of exercise is introduced. Research comparing the effect of different rehabilitation programmes is lacking as is evidence to guide post-operative rehabilitation. Recent progress in surgical procedures and diverse populations presenting with ASD partly causes this variability. Wang and colleagues, suggested a three-phase protocol:
Phase 1 Immobilisation (up to 6 weeks). Goal is to maintain anterior-inferior stability

• It has traditionally been thought to be immobilized with internal rotation, but according to Miller, immobilization has been beneficial in external rotation because there is more contact force between the glenoid labrum and the glenoid. 
• Research by Itoi suggests immobilization at 10 degrees of external rotation has a lower recurrence rate than internal immobilization at 10 degrees. 
• There is currently no consensus on the duration of immobilization in a sling. 
• Typical time periods in a sling range for 3-6 weeks if under the age of 40 and 1-2 weeks if older than the age of 40. 

During the immobilization period, the focus is on AROM of the elbow, wrist and hand and reduction of pain. Isometrics can be incorporated for the rotator cuff and biceps musculature.eg Codman Exercises; AAROM for external rotation (0-30º) and forward elevation (0-90º)
Phase 2 (6-12 weeks): Goal is to restore adequate motion, specifically in external rotation

• AAROM to achieve a full range of motion when stretching is permitted, passively stretch the posterior joint capsule through the use of joint mobilizations or self-stretching.
• No strengthening or repetitive exercises should start until the achievement of the full range of motion

Phase 3 (12-24 weeks): Successful return to sports or physical activities of daily living

• Begin strengthening exercise, strengthening exercises should be impairment-based.
• Typically begin strengthening exercise in a pain-free motion with exercises for stability.
• A possible progression could begin by focusing on the rotator cuff musculature and scapular stabilizers, which include trapezius, serratus, levator scapulae, and rhomboids. Then, progress to the larger musculature such as the deltoids, latissimus dorsi, and pectorals.
• Start focusing on functional exercises include proprioceptive training, tailor to promote patient's activities and participation in society
• See also Return to Play in Sports

Posterior Dislocation

Management for posterior dislocation follows the same progression as anterior protocol, except for the following guidelines:
a. Posterior glide is contraindicated
b. Avoid flexion with adduction and internal rotation
c. Immobilized 3-6 weeks if less than 40 years of age and 2-3 weeks if greater than 40 years of age
d. Strengthening will focus primarily on posterior musculature such as: infraspinatus, teres minor and posterior deltoid

See also Return to Play in Sports

Differential Diagnosis

• Fracture (clavicle, glenoid, humeral head, greater tuberosity, and proximal humerus)
• Rheumatoid Arthritis
• Rotator Cuff Injury
• Acromioclavicular Joint Dislocation
• Labral Pathology
• Shoulder Subluxation
• Axillary Nerve/Suprascapular Nerve Palsies