eMedicine Specialties > Sports Medicine > Shoulder

Shoulder Dislocation

L. Edward Seade, MD, Chief of Shoulder Service, Orthopaedic Specialists of Austin
Robert Josey, MD, Consulting Staff, Department of Orthopedic Surgery, Orthopaedic Specialists of Austin
Contributor Information and Disclosures

Updated: Dec 8, 2008

Introduction

Shoulder dislocations may occur from a traumatic injury or from loose capsular ligaments. Different conditions may affect the stabilizing structures of the shoulder and, thus, negatively affect patients with shoulder dislocations.¹

Background

This article focuses on glenohumeral joint dislocation. Although acromioclavicular (AC) joint separations are sometimes called shoulder dislocations by nonmedical persons, these are not true shoulder dislocations. Shoulder dislocations occur when the head of the humerus comes out of its socket, the glenoid.

For excellent patient education resources, visit eMedicine's Breaks, Fractures, and Dislocations Center and Sports Injury Center. Also, see eMedicine's patient education articles, Shoulder Dislocation and Shoulder Separation.

Frequency

United States

• The shoulder is the most commonly dislocated joint in the body.^{1, 2, 3}
• Although most shoulder dislocations occur anteriorly, they may also occur posteriorly, inferiorly, or anterior-superiorly.
• Patients with a previous shoulder dislocation are more prone to redislocation.
• Other factors that show a clear correlation to redislocation are the age of the patient and concomitant rotator cuff tears and fractures of the glenoid.
  • Younger patients (teenagers and those aged 20 years) have a much higher frequency of redislocation than patients in their 50s and 60s.⁴ Many physicians believe that age is less of a predisposing risk factor for redislocation than activity level.
  • Patients who tear their rotator cuffs or fracture the glenoid during their shoulder dislocation have a higher incidence of redislocation than patients without these problems.

Functional Anatomy

Shoulder stability is maintained by the glenohumeral ligaments, the joint capsule, the rotator cuff muscles, the negative intra-articular pressure, and the bony/cartilaginous anatomy.

The main stabilizers of the shoulder joint are the ligaments and the capsule complex. Multiple ligaments are present, but the inferior glenohumeral ligament is the most important and the one most commonly injured during an anterior shoulder dislocation. The injury may be a tear of the ligament/capsule off one of its bony attachments, and/or it may cause a stretch injury to these structures.

Tears in the rotator cuff muscles may also lead to shoulder instability. Four rotator cuff muscles are present in the shoulder. They are found superficial to the glenohumeral ligaments and the bones. Large tears may lead to shoulder instability, even with intact glenohumeral ligaments. Instability of the shoulder can also occur from injury to the nerves that control the shoulder muscles, specifically the axillary nerve.

Sport-Specific Biomechanics

The shoulder is a very mobile joint; therefore, it is often placed in awkward positions during sports. Thus, the force from a fall or a blow may be sufficient to cause shoulder damage. If the force is strong enough, the athlete tears the ligaments/tendons, fractures the glenoid or humerus, and dislocates the shoulder.

Clinical

History

Patients with a dislocated shoulder report a myriad of symptoms to their physician.

• Because most dislocations happen from trauma, patients report feeling the shoulder pop out during the incident. Different shoulder positions during the dislocation tear different ligaments. Thus, trying to determine the shoulder position at the time of the injury is important. The most common dislocation is anterior. In an anterior dislocation, the patients report having their arm abducted and externally rotated.
• Ask the patient if they had to go to the emergency department to have the shoulder reduced. If they did, they should have a radiograph of the dislocated shoulder. If they did not go to the emergency department, did the patient pop the shoulder back in or did it just go back in by itself?
• Patients with very loose joints (hyperlaxity) report feeling like their joint rolls out of the socket. These patients can usually "roll" the shoulder back in.
• Remember that patients with previous shoulder dislocations are more apt to redislocate, so ask about any previous dislocations.
• Some patients feel stingers or numbness run down their arm at the time of the dislocation.

Physical

The physical examination in a patient suspected of having a dislocated shoulder should confirm what the clinician picked up from the history of the injury.

• If the patient has a dislocated shoulder, range of motion (ROM) is poor and the patient is in a lot of pain. If the shoulder is anteriorly dislocated, the arm is in slight abduction and external rotation. In patients who are thin, the prominent humeral head can be felt anteriorly and the void can be seen posteriorly in the shoulder.
• Posterior shoulder dislocations can be easy to miss, because the patient usually keeps his or her arm in internal rotation and adduction (ie, the patient holds the arm up against his or her abdomen). In patients who are thin, the prominent head can be seen and palpated posteriorly. Poster shoulder dislocations can be missed, because the patient appears to only be guarding the extremity. If the proper radiographs are not obtained, the diagnosis will be missed (see Imaging Studies).
• Performing a detailed neurovascular examination before and after the shoulder has been reduced is imperative. Injury to the axillary nerve during shoulder dislocation has been reported to be as high as 40%. 

Causes

Approximately 95% of shoulder dislocations result from a major traumatic event, and 5% result from atraumatic causes. Distinguishing the type and severity of the event is important to determine the true etiology of the dislocation. This distinction is necessary to determine the treatment.^{1, 2, 5, 6, 7}

With a traumatic dislocation, the cause is obvious; however, atraumatic dislocations can result for different reasons. Ligamentous lax shoulders may dislocate with little or no trauma. Patients with lax ligaments may have 2 loose shoulders, but only 1 may be symptomatic. Congenital causes, such as excessive retroversion of the humeral head or malformation of the glenoid, can lead to instability. Neuromuscular causes, such as injury to the axillary nerve or cerebral palsy, have also been associated with shoulder instability.

References

• Acromioclavicular Joint Injury
• Bicipital Tendonitis
• Clavicular Injuries
• Rotator Cuff Injury
• Shoulder Dislocation
• Swimmer's Shoulder

• Breaks, Fractures, and Dislocations Center
• Sports Injury Center
• Shoulder Dislocation Overview
• Shoulder Dislocation Symptoms
• Shoulder Dislocation Treatment
• Shoulder Separation Overview