Anterior Glenohumeral Joint Dislocation

Etiology

The majority of acute anterior shoulder dislocations are caused by trauma. This includes fall onto an outstretched arm or with the arm overreached in the elevated and externally rotated position.[4] In cases of recurrent dislocations, associated disruption of the stabilizers of the shoulder should be suspected. In younger patients, underlying labral or glenoid pathology is typically sustained. In patients greater than 40 years old, rotator cuff tears are more likely to cause recurrent instability.[5][6]

Epidemiology

The number of initial and recurrent traumatic shoulder dislocations is estimated at 11.2 per 100,000.[7] The highest incidence of anterior shoulder dislocation is seen between the ages of 15 to 30, with a male to female ratio of 2.64.[8]

Pathophysiology

In an anterior dislocation, the arm is an abducted and externally rotated position. In the externally rotated position, the posterosuperior aspect of the humeral head abuts and drives through the anteroinferior aspect of the glenoid rim. This can damage the humeral head, glenoid labrum, or both. An associated humeral head compression fracture is described as a Hill Sach's lesion. If large enough, it can lead to locked dislocations that may require open reduction. The glenoid labrum is a fibrocartilaginous structure that rings the circumference of the glenoid fossa. Bankart lesions are injuries to the anteroinferior glenoid labrum complex and the most common capsulolabral injury. A "bony Bankart" lesion refers to an associated fracture of the glenoid rim. These capsulolabral lesions are risk factors for recurrent dislocation. 

Axillary nerve injury is identified in about 42% of acute anterior shoulder dislocations. Nerve transection is rare, and traction injuries are more common.[8] Arterial injury has also been described. The subclavian artery becomes the axillary artery after passing the first rib. The distal portion of the axillary artery is anatomically fixed and, therefore, susceptible to injury in anterior dislocations. Ischemic injury, including pseudoaneurysm and arterial laceration, is rare but carries marked morbidity if not quickly identified.[7]

History and Physical

A complete history and exam must be performed to capture associated occult trauma and especially prior to closed reduction maneuvers and associated procedural sedation. Shoulder joint evaluation should be systematic in nature. The shoulder complex is composed of three joints, the sternoclavicular (SC), acromioclavicular (AC), and GH joint, and the surface anatomy of each joint should be inspected and palpated to confirm integrity. The humeral head of the GH joint can be seen and palpated in a pathologically anterior position. A thorough neurovascular examination must be performed and additionally documented before any reduction maneuvers. The axillary nerve is particularly predisposed to injury due to its anatomic course along the proximal aspect of the humeral neck and quadrilateral space before innervating the deltoid muscle. The function of the axillary nerve is confirmed by intact sensation at the proximal brachium ("sentinel patch") and firing of deltoid muscle abduction. Axillary artery integrity should be confirmed with signs of distal perfusion and intact pulses, and the absence of axillary swelling or expanding hematoma.[9][10][11]

Evaluation

Plain radiographs with multiple views are requisite for the initial evaluation of all traumatic injuries of the shoulder. The anteroposterior view will demonstrate cranial-caudal displacement. An orthogonal view is required to assess anteroposterior displacement. The axillary view places the patient's arm in abduction with the beam-directed cranial-caudal. This view is often difficult to obtain due to pain or due to the dislocation itself, limiting abduction. Modifications such as the Velpeau view are helpful in these situations. The Velpeau view does not require abduction, and the patient's arm can remain in a sling. The patient leans back obliquely 30 to 40 degrees over a cassette, and the beam is directed cranial-caudal. The scapular Y view is used to assess the humeral head position and directionality relative to the glenoid if other views are difficult to interpret.

Advanced imaging is not commonly indicated in the acute setting if diagnostic radiographs are complete. Further outpatient radiographic evaluation includes Stryker notch views to assess Hill Sachs lesion on the humeral head or Westpoint views to assess bony involvement on the glenoid.[12] Magnetic resonance arthrograms evaluate labral pathology in younger patients. Magnetic resonance imaging should be considered in older patients to assess for concomitant traumatic rotator cuff tears. Computer tomography is useful in cases of chronic dislocations to determine the degree of the humeral head or glenoid bone loss to plan treatment options.[13]

Treatment / Management

An acutely dislocated shoulder demands timely closed reduction. Delaying reduction over 24 hours increases the risk of unstable reductions, muscle spasm, neurovascular compromise.[7] Throughout history, there have been numerous described closed reduction techniques. The most ancient of which, the Hippocratic method, involves placing the physician's foot into the patient's axilla as counter-traction while applying traction along the upper extremity, has fallen out of favor given the risk of iatrogenic brachial plexus and vascular injury. The choice of reduction maneuver is provider and patient-dependent.[14] Intraarticular anesthetic injection, or less frequently, procedural sedation, is required for adequate relaxation of GH active stabilizers. Several of the commonly performed reduction maneuvers are described below.(A1)

Kocher Method

The Kocher method was originally described in 1870. The patient is supine with the elbow flexed to 90 degrees. The arm is then externally rotated until resistance is met. The clinician then adducts and internally rotates the shoulder until reduction is felt. This technique does not involve traction. Modifications to this technique include additional traction.[15]

Milch Technique

The patient is supine. The clinician holds the wrist or elbow and applies axial traction while externally rotating and abducting the arm.[1](A1)

Spaso Technique

Described in 1998, this technique involves traction and external rotation. The patient is supine, and the shoulder forward flexed to 90 degrees. The physician applies vertical axial traction and then external rotation.[15]

Traction and Countertraction: This method requires an assistant to provide counter-traction. The patient is supine with a sheet wrapped around the thorax to be held by an assistant on the contralateral side. The clinician applies in-line axial traction to the affected arm while the assistant provides counter-traction.[1](A1)

FAst, REliable, and Safe (FARES) Method

The patient is supine. Axial traction is applied with the arm in a neutral position. Gentle anterior-posterior oscillating movements (such as seen with handshaking) is applied as the arm is brought into abduction and external rotation.[16] Sayegh et al. performed a prospective randomized study comparing their FARES method with the Hippocratic and Kocher method and found a shorter time to successful reduction and lower self-reported pain scores relative to the two classic methods(A1)

Boss-Holzach-Matter Self-Assisted Technique

This is a self-reduction technique. The patient is seated with the ipsilateral knee flexed to 90 degrees. The patient is then asked to interlace both hands around the knee. The patient then leans back until their arms are fully extended while instructed to shrug their shoulders forward. Marcano-Fernandez et al. found this method to be as effective and less painful compared to the Spaso technique with the added benefit of patient education.[17][18](A1)

Upon successful closed reduction, perform a post-procedural exam, obtain confirmatory post-reduction radiographs, and immobilize the shoulder in a sling.

Differential Diagnosis

The directionality of shoulder dislocation must be confirmed on prereduction radiographs. Posterior dislocation can occur in seizure or electric shock. They are often missed on presentation to the emergency room. Unlike anterior shoulder dislocations, patients present with the affected extremity in internal rotation with decreased external rotation.[19] Isolated lesser tuberosity fractures are uncommon but associated with posterior shoulder dislocations. If a patient presents with an isolated lesser tuberosity fracture, a primary posterior shoulder dislocation should be investigated. Inferior shoulder dislocations (luxatio erecta) are the rarest of shoulder dislocations. They are the result of high-energy trauma. As the name implies, patients present with the arm in a hyper-abducted position. These dislocations have a high association with neurovascular injuries.[20][21]

The SC and AC joints of the shoulder complex can be concomitantly disrupted. AC joint separation can be mistaken for shoulder dislocations. They account for 9% of shoulder girdle injuries.[22] The Rockwood classification system identifies six types of injuries increasing in severity, and are based on radiographic criteria.[23] The Zanca view can be added to standard clavicle X-ray and is performed with the beam oriented 30 degrees cranial to the clavicle. 

Proximal humerus fractures present similarly or concomitantly. Fractures can demonstrate increased ecchymosis, suggesting soft tissue or osseous injury. Proximal humerus fracture dislocations can have a completely displaced humeral head. Closed reduction is often unsuccessful. An emergent orthopedic surgery consultation is recommended in these injuries as urgent open reduction may be required.

Treatment Planning

Acute management consists of closed reduction and immediate immobilization. The position of immobilization remains a topic of debate. A recent systematic review did not demonstrate any benefit to immobilization in external rotation over internal rotation in the risk of redislocation and return to sports functionality.[7] Additionally, immobilization in external rotation is a more non-functional position for the patient. Immobilization in external rotation should be considered for posterior dislocations, as adduction with internal rotation is a position of instability for these types of dislocations. The described duration of immobilization also varies from one to six weeks.[24] There remains a need for high-level studies comparing the method and duration of immobilization.[7] 

Long-term treatment plans are tailored to patients depending on age, activity level, and history of recurrent dislocation or chronic instability. In younger patients, surgical planning should be implemented, given the high rates of redislocation. Age is the primary predictor of recurrence, with the highest rates seen in patients less than 30 years old.[8] Lesions such as the Hill Sach's, Bankart, and bony Bankart lesions are injuries associated with anterior shoulder dislocations. There is a 73% prevalence of concomitant Bankert lesions.[7] Over 20% of damage to the glenoid can be an indication for surgical evaluation. Recurrence rates are extremely varied but can be as high as 70%.[7] The quantification of these bony lesions is important in dictating operative management and decreasing the risk of recurrence. With isolated Bankart lesions, arthroscopic labral repairs can be successful. If the patient is younger, or has more involved pathology, a simple arthroscopic procedure may not be as successful.

The instability severity index score was developed to help guide treatment between an arthroscopic procedure versus an open stabilization procedure.[25] In cases of excessive bony involvement, more extensive procedures are required. For severe humeral head lesions, the Remplissage procedure has been successful in decreasing redislocation. Remplissage, which in French means "to fill," fills the humeral head defect with the posterior capsule and infraspinatus to prevent the humeral head from engaging with the glenoid. For extensive glenoid loss, coracoid transfer procedures, such as the Latarjet, prevent redislocation by multiple mechanisms. A transferred section of the coracoid process offers static stabilization by filling in the bony defect and performing as a bony block. The conjoint tendon, which is transferred with the coracoid, has a sling effect offering dynamic stabilization.[26] In older patients with rotator cuff tears, rotator cuff repair versus a reverse total shoulder arthroplasty should be considered given patient age, activity level, rotator cuff tissue quality, and pre-existing glenohumeral arthritis.

Controversy remains for the first-time dislocation. Some authors propose non-operative management and a rehabilitation protocol in the initial management of older patients and younger patients not involved in overhead activities.[27] If non-operative treatment is pursued, a rehabilitation protocol entails regaining motion, dynamic stabilization, neuromuscular training, and strengthening. The initial phase may be dedicated to symptomatic management of pain and gentle range of motion. As range of motion is regained, and pain subsides, attention can be turned to active range of motion and strengthening. The later stages of rehabilitation can then focus on advanced strengthening with a gradual return to activity.

Prognosis

Recurrence and prognosis are highly dependent on age and activity level. Multiple studies cite incidence rates with certain contact sports. There is an up to 92% recurrent shoulder dislocation rate in patients less than 25 years old and participating in a contact sport. In patients over 30, the recurrence is approximately 72%. Depending on the initial age of injury, follow up, and Bankart lesion repair, patients may develop arthropathy in addition to chronic instability. Arthropathy is seen in approximately 28% to 67% of those that undergo a Bankart repair, which may be due to chondral damage due to repeated dislocations.[24]

Complications

Continued instability is a risk for both operative and non-operative management. With advances in surgical techniques, stabilization procedures in high-risk patients have become more successful in decreasing recurrence.[28][29][30]

Surgical complications must be considered. With capsular and labral repair, overtightening or prolonged immobilization can lead to stiffness. Bone block procedures may have complications with graft incorporation and hardware complications. In their 2019 systematic review, Williams et al. cited complications rates of 1.6%, 0.5%, 6.2%, 2.3%, 7.2%, and 13.6% for arthroscopic soft tissue repair, arthroscopic soft tissue repair with arthroscopic remplissage, open soft tissue repair, open labral repair with remplissage, open bone block procedures, and arthroscopic bone block procedures respectively. They cited a 10-fold increase in complications with bone block procedures.[31] Intuitively, higher complication rates were seen in the more technically demanding procedures, which also may reflect more significant pre-operative injury.