Posterior Shoulder Dislocations

Posterior Shoulder Dislocations are less common than Anterior Shoulder Dislocations

The shoulder joint:

The anatomic configuration of the shoulder joint known as the glenohumeral joint is often compared to a golf ball on a tee. It is the most mobile joint in the body allowing the arm to move in many directions which is why it is the most frequently dislocated joint in the human body. The stability and movement at the shoulder is controlled by the rotator cuff muscles, ligaments, and the capsulolabral complex of the shoulder. There are three main types of dislocations depending on displacement direction of the humeral head: anterior, inferior and posterior. Posterior dislocations also known as Reverse Hill-Sachs lesion are those in which the humeral head has moved backward toward the shoulder blade and  they attribute to 4% of all shoulder dislocations.

Causes:

Dislocations of the shoulder occur when the head of the humerus is forcibly removed from its socket in the glenoid fossa. The most common cause for posterior dislocations is anterior trauma to the shoulder such as blunt force. Seizures (epileptic, hypoglycemic, drug-induced, etc.) or electric shocks such as being hit by lightning or being electrocuted can also cause unilateral or bilateral posterior dislocations due to unbalanced muscle contractions pulling the humeral head backwards. Sport activities that may lead to posterior shoulder instability include heavy bench pressing and football linemen blocking. Other sports where this type of dislocation is commonly seen are basketball and volleyball.

Symptoms:

Patients with posterior shoulder instability frequently report aching pain and weakness along the posterior or anterior joint line, the biceps tendon, and/or the superior aspect of the rotator cuff. Symptoms intensify with the arm in 90° forward flexion, adduction (close to the body), and internal rotation (reaching back). Dislocations may also cause numbness, weakness or tingling near the injury, such as in your neck or down your arm. The muscles in your shoulder may spasm from the disruption, often increasing the intensity of your pain. When the shoulder dislocates posteriorly the capsule, ligaments and labrum may tear causing increasing pain and restricted motion.

Diagnosis:

Diagnosis is often delayed and this leads to a locked posteriorly dislocated humeral head. Plain X-rays may be taken to confirm the diagnosis of shoulder dislocation and to make certain there are no fractures associated with the dislocation. Severe edema after the injury hinders the diagnosis so the clinical examination must be done carefully. During physical examination the anterior aspect of the shoulder may seem to be flattened and the patient may present with pain at both the anterior and the posterior aspects of the shoulder region with limited range of motion, especially in abduction and external rotation (away from the body). Clinical picture may resemble other shoulder pathologies such as frozen shoulder, shoulder sprain or a rotator cuff tear. In up to 79% of cases, the diagnosis is made only once the injury has become chronic and the shoulder has been locked, which unfortunately has a negative effect on prognosis.

Treatment:

Treatment strategy varies from conservative treatments to operative options.

Conservative treatments could be:

Operative treatments could be:

Closed reduction is the initial treatment for all acute posterior dislocations and immobilization with a sling is important to decrease the risk of a repeat dislocation. Medications may be required for sedation to help relax the muscles surrounding the shoulder and facilitate the reduction. In order to reduce the humeral head into the glenoid fossa, forward pressure on the humeral head must be applied with the arm in the flexed, adducted (close to the body) and internally rotated position (across the body). After the closed reduction, the arm must be kept in a gunslinger splint with 10° of abduction (away from the body) and neutral rotation for approximately six weeks. Once the shoulder has been reduced a post reduction X-ray is recommended to reexamine the arm and make certain that no damage occurred during the reduction procedure. Activities that require to place the arm in high-risk positions such as hyper internal rotation (across the body) are prohibited until 12 weeks.

Open reduction is indicated in dislocations in which a closed reduction cannot be achieved such as in cases where defects to the humeral head articular surface ranges from 25% to 45%. If the injury is less than 3 weeks old, disimpaction and bone grafting of the defect can be performed. In the case of larger defects of up to 50% and young patients with viable humeral bone reserve, fixation of the allografts in defective areas with partially threaded cancellous screws yielded excellent results.

Complications:

Some complications are:

Recovery time:

The functional outcomes depend mainly on the duration of the dislocation and the extent of the articular injury. In shoulder dislocations not associated with a fracture, other injuries or in younger patients the shoulder should be kept immobilized for two to three weeks. In the elderly, this time frame may shrink to only a week because the risk of developing frozen shoulder (a joint that becomes totally immobile) is markedly increased. Physical therapy is necessary for rotator cuff strengthening, periscapular stabilization and to return normal function to the shoulder joint. Therapy may include exercises to strengthen the muscles that surround the shoulder and to maintain range of motion of the shoulder joint. The total rehabilitation and recovery time from a shoulder dislocation is about 12-16 weeks.

Prognosis:

Future prognosis depends on the extent of damage to the articular joint of the humeral head; duration of the dislocation and patient specific conditions such as age and activity level. Age is the major factor as to whether there will be another dislocation. The younger the patient, the more likely that another dislocation will occur. If the first dislocation happens before age 20, there may be up to a 95% chance that there will be a second dislocation in the future. With an age of 20 to 40, the risk of future dislocation decrease to less than 50%. After the age of 40 every ten years the risk drops by 10%. 

Author
Endrina Mangual Valladares Third year Medical Student at University of Medicine and Health Sciences (UMHS)

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