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] Show Note the images and video below.  Shoulder dislocation, Part 1. 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. Workup and treatmentWhen dealing with shoulder instability, obtaining 2 orthogonal views of the shoulder is imperative. Magnetic resonance imaging (MRI) can show damage to ligaments that may be torn with shoulder dislocation. They are better seen with the injection of contrast into the joint before the MRI evaluation. The bony architecture on these studies can also be appreciated. The most important treatment of an acute shoulder dislocation is prompt reduction of the glenohumeral joint. [1, 2, 3] Numerous reduction techniques have been described that can be performed after administering an intra-articular injection or after putting the patient under conscious sedation. After determining the direction of the dislocation, the physician must remember that the most important aspect of reduction is relaxation of the shoulder musculature. Once reduction has been accomplished, postreduction radiographs are necessary to verify reduction. In the acute phase of a dislocated shoulder, therapy should be limited. The arm should be immobilized in a sling and swathed for 1-3 weeks. While the patient is in the sling, elbow, wrist, and hand range of motion (ROM) should be encouraged. Working with the parascapular muscles is also important during this acute phase of rehabilitation, since this can be initiated while the patient is still in the sling. These exercises should be continued when the patient comes out of the sling. Active and passive flexion, extension, abduction, and internal/external rotation begin at about the third week, when the patient comes out of the sling. After the initial period of immobilization, passive ROM exercises should begin. More vigorous therapy can be initiated after full passive ROM has been regained, usually after 6 weeks. In patients who have recurrent shoulder instability, operative care should be highly considered. [4, 2, 5] The goal of an operative repair is to reattach the torn tissue back to the place where it tore off of the bone. Recurrent shoulder dislocations also stretch out the ligaments. It is imperative to also address the tissue laxity during the operative procedure. Related Medscape Reference topics include the following:
EpidemiologyUnited States statisticsThe shoulder is the most commonly dislocated joint in the body. [1, 4, 6] 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. This occurs because the tissue does not heal properly and/or because the tissue stretches out and becomes more lax. 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. [7] 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. In a retrospective cohort study, Kardouni et al found the 10-year incidence rate of shoulder dislocations in US Army soldiers to be 3.13 per 1000 person-years, or a total of 15,426 incident shoulder dislocations. The recurrence rate was 28.7%. Injury risk was greater in males and soldiers aged 40 years or younger, with recurrence risk increased by concurrent axillary nerve injury and age of 35 years or less. [8]
Functional AnatomyShoulder 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 (supraspinatus, infraspinatus, subscapularis, and teres minor) are present in the shoulder. They are found on top of the glenohumeral ligaments and the bones. Large rotator cuff 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 BiomechanicsThe shoulder is a very mobile joint; therefore, it is often placed in awkward positions during sports (specifically abduction and external rotation). Thus, the force from a fall or a blow may be sufficient to cause damage to the ligaments. If the force is strong enough, the athlete may tear the ligaments/tendons, fracture the glenoid or humerus and from this, dislocate the shoulder.
EtiologyApproximately 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, 4, 9, 2, 5] 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.
PrognosisAge at dislocation is the most important prognostic indicator for recurrence of shoulder dislocations. Younger age at initial injury increases the likelihood for future dislocation. The recurrence rate is thought to be 90% if the initial episode occurs in the teen years. In patients aged 40 years or older, the recurrence rate is 10-15%. Most redislocations occur within 2 years of the primary injury. Persons with axillary nerve injuries can be expected to recover completely within 3-6 months. ComplicationsThe most common complication of an acute shoulder dislocation is recurrence. This complication occurs because the capsule and surrounding ligaments are stretched and deformed during the dislocation. Age is the most important indicator for prognosis; dislocations recur in approximately 90% of teenagers. Another common complication following dislocation is fracture. The most common type is a Hill-Sachs lesion or compression fracture of the posterior humeral head. Fractures of the proximal humerus, greater tuberosity, coracoid, and acromion have also been described. Rotator cuff tears also commonly occur as a result of shoulder dislocations, and the frequency of this complication increases with age. This complication can be expected in 30-35% of patients aged 40 years or older. Slow progression in return to active function following shoulder dislocation in a middle-aged patient should warrant a workup for a rotator cuff tear. Vascular injuries are rare, but they do occur, especially in older patients. Vascular injuries are more common with inferior dislocations and usually involve a branch of the axillary artery. Nerve injuries are much more common than vascular injuries, especially with anterior or inferior dislocations. The axillary nerve is the nerve injured most often and may be crushed between the humeral head and the axillary border of the scapula or injured by traction from the humeral head. Axillary nerve injury has been reported in as many as 33% of acute anterior dislocations.
Patient EducationEducate the patient on the importance of strength training following shoulder dislocation. The patient must understand that recurrence is possible and therapy should be used to prevent recurrence. For more patient education information, see Shoulder Dislocation Diagnosis and Treatment.
Author Specialty Editor Board Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference Disclosure: Received salary from Medscape for employment. for: Medscape. Henry T Goitz, MD Clinical Professor of Orthopaedic Surgery and Sports Medicine, Michigan State University College of Human Medicine; Academic Chief of Orthopaedic Sports Medicine, Regional Director of Ambulatory Clinic Site, Sports Medicine Institute, Detroit Medical Center Henry T Goitz, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American Orthopaedic Society for Sports Medicine, Arthroscopy Association of North America, Detroit Academy of Orthopaedic Surgeons, International Association for Dance Medicine and Science, International Society of Arthroscopy, Knee Surgery and Orthopaedic Sports Medicine, Michigan Orthopaedic Society, Michigan State Medical Society, Mid-America Orthopaedic Association Disclosure: Nothing to disclose. Chief Editor Additional Contributors Joseph P Garry, MD, FACSM, FAAFP Associate Professor, Department of Family Medicine and Community Health, University of Minnesota Medical School Joseph P Garry, MD, FACSM, FAAFP is a member of the following medical societies: American Academy of Family Physicians, American Medical Society for Sports Medicine, Minnesota Medical Association, American College of Sports Medicine |
