Acute shoulder dislocations

The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Department of the Army, Department of Defense, nor the U.S. Government.

Introduction

Acute shoulder instability encompasses a broad range of injuries and pathologies ranging from subluxation to dislocation and including mulitidirectional instability and posterior and anterior instability. Acute traumatic shoulder instability is common in young athletes, especially those participating in contact sports.^1,2 Recurrent instability is more common in younger patients and athletes. Treatment is tailored to the pathoanatomy.

The incidence of shoulder dislocation is approximately 24 per 100,000 person-years in the general population.³ However, it has been noted that subluxations account for up to 85% of shoulder instability events compared to the 15% of dislocations.⁴ The highest injury rates have been reported among young males (age 15-25) and military personnel.^3,5

Anatomy

The articulation between the proximal humerus and the glenoid provides little inherent stability and few osseous restraints, allowing the shoulder joint to have the greatest range of motion of any joint in the body. The stability of the glenohumeral joint depends on the soft tissue restraint of the capsule, labrum, ligaments, and muscles. As a result of these stabilizers, the humeral head translates only 1 mm from the center of the glenoid during active motion.⁶

Glenohumueral Joint

The oval-shaped glenoid is longest in the inferior to superior direction and is slightly deeper in the center compared to the periphery. The scapula lies on the posterior thoracic wall and faces anterior and superior in continuity with the glenoid neck. The articular surface is orientated 35° anterior and 5° superior, providing increased posterior and inferior stability. The proximal humerus is retroverted approximately 30° to 40° relative to the distal humeral epicondyles to match the anteversion of the glenoid. 

Labrum

The labrum is a dense fibrous connective tissue that serves as an attachment for capsuloligmentous structures and provides increased depth to the glenoid articulation, which increases shoulder stability. The glenoid labrum is firmly attached to the glenoid rim inferiorly and more loosely attached superiorly, with variable normal anatomic morphology at the remainder of the glenoid rim. 

Glenohumeral Ligaments

The glenohumeral ligaments are confluent with the shoulder capsule and serve as static stabilizers to the shoulder. The superior glenohumeral ligament courses within the rotator interval and above the biceps tendon and is an important restraint to inferior translation with the arm in an adducted position. The middle glenohumeral ligament runs posterior to the subscapularis and is an important stabilizer against anterior humeral head translation with the arm in 45° of abduction and external rotation. The course and anatomy of the middle glenohumeral ligament is highly variable. A Buford complex is a cord-like middle glenohumeral ligament and absent anterosuperior labrum, which maybe confused with a pathologic labral tear. The inferior glenohumeral ligament consists of an anterior and a posterior band, which are important stabilizers against inferior humeral head translation with the arm in 90° of abduction. 

Neurovascular Structures

The proximal humerus is supplied by the anterior and posterior circumflex arteries. The posterior humeral circumflex artery courses with the axillary nerve inferior to the teres minor and through the quadrangular space. The axillary nerve is as close as 2 mm inferior to the joint capsule, making this nerve prone to iatrogenic injury in inferior capsular dissection or arthroscopy. The axillary nerve is the most commonly injured nerve resulting from an anterior dislocation event. The musculucutaneous nerve is the most medial structure of the brachial plexus and passes medial to the conjoint tendon 3-5 cm below the coracoid. 

Pathogenesis

Traumatic injuries are the most common cause of shoulder instability and account for 95% of anterior shoulder dislocations. Indirect force with the arm in an abducted and externally rotated position increases the anterior translational forces of the humerus within the glenoid. In this position, the anterior band of the inferior glenohumeral ligament and the anterior inferior labrum detach from the glenoid producing the “essential” lesion of anterior shoulder instability, the “Bankart lesion” (Figure 1). This has been reported to occur in 97% of traumatic anterior dislocations events⁷ and 96% of traumatic anterior subluxation events.⁸ Anteroinferior labral detachment, therefore, disrupts the main anterior static restraints to the glenohumeral joint in the abducted and externally rotated position, and this must be identified and repaired to prevent further instability events.⁹ In some cases, the anteroinferior glenoid may fracture, creating a bony Bankart. Anterior instability may lead to a humeral avulsion of the glenohumeral ligament (HAGL) in less than 10% of instability events.¹⁰ The Hill-Sachs lesion is the corresponding humeral lesion to the glenoid Bankart. Hill-Sachs lesions are postero-superior compression fractures on the humeral head. 

Figure 1. Arthroscopic image of Bankart lesion

Multidirectional instability may be due to generalized ligamentous laxity, and it is not limited to anteroinferior instability; thus, it is recognized as a distinct pathologic entity from traumatic anterior shoulder instability. Often, mulitidirectional instability secondary to ligamentous laxity leads to recurrent instability events; however it is not associated with the classic Bankart lesion. 

Posterior instability accounts for approximately 10% of all instability, and subluxation events predominate.⁴ Posterior dislocation is uncommon and may result from seizures or electrical shock in which the more powerful pectoralis muscles produce an internal rotation and posteriorly directed force on the humeral head. Posterior subluxation is frequently encountered in athletes such as football linemen who encounter repetitive direct posterior forces. Posterior instability may produce a posteroinferior glenoid lesion (reverse Bankart lesion) and an anterosuperior humeral head lesion (reverse Hill-Sachs lesion). 

Natural History

The natural history of initial shoulder dislocations remains controversial. Recurrent dislocation is most strongly predicted by the age of the patient.^11-14 In athletes younger than 20 years of age, recurrence rates ranging from 61% to 94% have been reported in non-operatively managed shoulder dislocations.^11-14 Recurrent dislocation following an initial anterior shoulder dislocation is less common in older patients, and in those between ages 51 and 60 years, the recurrence rate is 27%.¹⁵

Some authors have argued that acute, initial, anterior shoulder dislocations in young, active adults could be improved with operative capsulolabral repair in the acute period.^16-22 There is ample level 1 evidence that acute arthroscopic stabilization is superior to nonoperative management of first-time anterior dislocation events in young athletes, using both recurrent instability as well as subjective outcome measures.^17,18,23 The capsulolabral tissue in patients with acute injuries is robust and healthy in contradistinction to the atrophic and poor quality tissue that may be found in patients with recurrent instability or seeking a delayed repair.¹⁹ Others have reported, however, that after 25 years' follow up, only 7.9% continued to experience recurrent dislocations, 43% never redislocated, and 14.4% redislocated soon after the initial event but subsequently became stable over time. As a result, these authors concluded that operative management of initial shoulder dislocations in patients 25 years old or younger would result in an unnecessary surgery in 30% to 50% of cases.²⁴ 

Shoulder dislocations are particularly common in athletes and are more likely to occur during the intercollegiate competitive season. Owens et al¹ reviewed the National Collegiate Athletic Association database and reported that athletes were 3.5 times more likely to sustain a glenohumeral instability event during competition than during practices. Males were more likely to sustain a shoulder dislocation than females, and men’s spring football demonstrated the greatest injury rate, 0.4 injuries per 1,000 athlete exposures.¹ 

The optimal treatment of an in-season athlete who sustains a traumatic anterior glenohumeral subluxation or dislocation presents a significant dilemma to the treating orthopedic surgeon. The goal of the team physician is to return the athlete to competition in the safest and most efficient manner, minimize time away from competition, and restore function. Surgical stabilization for the treatment of acute glenohumeral instability that occurs during the athlete’s season mandates removal of the athlete from sports competition for 3 to 9 months. Buss et al.²⁵ examined the natural history of shoulder dislocations in in-season athletes and reported that in 30 high-school athletes, 90% returned to competition in the season and 37% experienced an episode of recurrent instability. The average number of days missed from sport was 10.7 days, with 46% of athletes undergoing surgical stabilization at the conclusion of the season.

In patients older than 40 years, the orthopaedic surgeon should have a high index of suspicion for concomitant rotator cuff pathology. These patients have a 30% incidence of concomitant rotator cuff tears, while those over 60 years old have an 80% incidence of rotator cuff tear. The treating orthopaedic surgeon should also be aware of the incidence of associated nerve injuries. Axillary nerve injuries, most often a neuropraxia, are seen in approximately 5% of anterior shoulder dislocations; however, radial nerve and musculocutaneous nerve injuries have also been reported.

Clinical Presentation

A thorough history is essential to characterize the patient’s shoulder instability. The patient may commonly recall a specific traumatic instability event, have numerous incomplete instability events, or describe generalized laxity of both shoulders and multiple other joints. Anterior instability is often reported with an injury when the arm is abducted and externally rotated. In contrast, posterior instability is often reported when injury occurs with the arm in an adducted, flexed, and internally rotated position. Inferior instability is accompanied by a history of instability with carrying heavy loads. Although anterior instability is significantly more common than inferior, posterior, or multidirectional instability, all pathology must be identified. 

The acute presentation of anterior shoulder dislocations is notable for a palpable prominence of the humeral head anterior and inferior to the shoulder and a lack of shoulder contour over the deltoid. The arm is generally held in a position of adduction and internal rotation, and abduction of the arm is limited to less than 90°. The acute presentation of posterior shoulder instability is more subtle and a lack of external rotation compared to the contralateral normal shoulder may be the only presenting sign. 

The physical exam should begin with evaluation of the asymptomatic shoulder for comparison. The following tests are used evaluate anterior, posterior and inferior instability.

Sulcus Sign

This test is performed by applying longitudinal inferior traction of the humerus while stabilizing the scapula. Inferior displacement of the humerus relative to the lateral border of the acromiom creates a sulcus. A 1+ sulcus sign represents 1 cm of inferior translation, 2+ is 2 cm of inferior translation, and 3+ is 3 cm of inferior translation. A 3+ sulcus sign is severe pathologic instability most often seen in patients with multidirectional instability.

Anterior Apprehension Test and Relocation Test

With the patient supine, the shoulder is brought to maximum abduction and external rotation. A positive test occurs when the patient exhibits guarding or apprehension during this maneuver. With the patient in this position, a positive relocation (Jobe’s test) is performed by placing a posteriorly directed force to the humerus, which causes the apprehension to disappear.

Load Shift Test

This test evaluates the degree of translation and can be performed in the seated or supine position at various levels of glenohumeral abduction. With one hand, an axial load is applied through the elbow to center the humeral head in the glenoid. An anterior and posterior directed force is then applied at 0°, 45°, and 90° of shoulder abduction. Increased translation at higher degrees of shoulder abduction implies compromise of the inferior glenohumeral ligament. A 1+ load shift is increased translation compared to the normal shoulder, 2+ translation is defined as humeral head translation over the glenoid rim but spontaneously reduces, and 3+ translation moves the humeral head over the glenoid rim without spontaneous reduction.

Imaging and Diagnostic Studies

History and physical examination are often sufficient to diagnose acute shoulder dislocations; however, radiographs clarify the diagnosis and evaluate for associated fractures or other injury. Initial radiographs should include an anteroposterior shoulder (Figure 2), a lateral or scapular Y view, and an axillary view. An axillary lateral view is important to assess posterior shoulder dislocations, and when this is unable to be obtained a Velpeau axillary radiograph can be performed to evaluate posterior translation. A Hill-Sachs lesion on the posterolateral proximal humerus is seen on the anteroposterior view with the humerus in internal rotation. A Stryker notch view is taken with the patient supine, the hand on the patients head, and the beam angled 10° from vertical to visualize the posterolateral humeral head. Glenoid fracture or deficiency is seen on the axillary view. Alternatively, the West Point view, taken with the patient prone, the humerus abducted to 90°, and the beam angled 25° from the floor, provides effective radiographic visualization of the anterior glenoid rim.

Figure 2. AP radiograph showing dislocated glenohumeral joint

If the patient has a glenoid fracture or there is suspicion of a large Hill-Sachs lesion, a CT scan is used to characterize the fracture and assist in surgical planning. CT is especially useful in patients with recurrent anterior shoulder dislocations as up to 49% have anteroinferior glenoid bone defects and 80% have Hill-Sachs lesions. MRI is used to evaluate soft tissue pathology and is more successful in detecting anteroinferior labral tears (Figure 3) than posteroinferior labral pathology. The addition of intra-articular contrast improves the sensitivity for labral tears and other intra-articular soft tissue pathology.

Figure 3. Axial cut MRI showing Bankart lesion

Classification

Glenohumeral instability is classified based on the degree, direction, frequency, and etiology:

• Shoulder instability may be a frank dislocation, requiring a reduction to relocate the proximal humerus, or a subluxation, defined as incomplete instability events that do not require an manual reduction maneuver.
• The direction of shoulder instability is unidirectional, bidirectional, or multidirectional.
• Shoulder instability is acute, recurrent, or locked. 
• The etiology of shoulder instability is traumatic, atraumatic, or acquired. 

Treatment

Non-Operative Treatment

Non-operative treatment of acute shoulder dislocations consists of closed reduction followed by a period of immobilization and then rehabilitation. The length and benefit of immobilization remains controversial. In older patients, with a lower likelihood of recurrence and increased propensity for stiffness, the period of immobilization might be limited to 2-3 weeks. In young athletes with higher rates of recurrence, some authors have reported reduced recurrence rates with immobilization for up to 5 weeks and restriction from activity for 6 weeks. 

Numerous techniques have been described for acute reduction of shoulder dislocations; however the Stimson and Traction-Countertraction are the most frequently used reduction maneuvers. 

• Stimson Technique - The patients is placed prone with the involved shoulder position at the edge of the table. A 5-lb weight is hung from the upper extremity for approximately 20 minutes, and after fatigue of the shoulder musculature, the joint is reduced. 
• Traction-Countertraction - With the patient supine, a sheet is placed around the torso to maintain countertraction, and then traction is applied to the arm in an inferior direction with approximately 30° of abduction. When the humerus is pulled laterally and disengaged from the inferior edge of the glenoid, gentle internal and external rotation assists with reduction into the glenoid.  Reduction performed with slow and constant forces allows the muscles to relax and minimizes the risk for fracture.

Rehabilitation should focus on strengthening the dynamic shoulder stabilizers, including the rotator cuff muscles, deltoid, pectoralis major, and latissimus dorsi. Provocative arm positions should be avoided in the early rehabilitation phase to allow the injured capsular restraints to heal. 

Operative Treatment

Operative treatment is indicated for a displaced greater tuberosity fracture more than 5 mm, anteroinferior glenoid defects >20% (inverted “pear shaped” glenoid), failure of non-operative treatment, and selective repair in young high-demand athletes. In young high-demand patients and athletes after a first time anterior shoulder dislocation, early arthroscopic Bankart repair has demonstrated reduced recurrence rates (75% vs. 11%), presumbably due to the improved tissue quality in the acutely treated first-time dislocator.  Not every first-time shoulder dislocator is an appropriate candidate for early stabilization; patient age, activity, shoulder use must be considered. Those who choose early stabilization over non-operative treatment will miss time from sport or activity as well as incur the inherent risks of surgery. 

Increasingly, Bankart repairs are performed using arthroscopic techniques, and many authors report equivalent results with open and modern arthroscopic techniques. The development of suture anchor technology allows capsular patholaxity, rotator interval deficiency, and labral pathology to be effectively addressed. Glenoid bone deficiency, an engaging Hill-Sachs, and severe capsuloligamentous laxity have been associated with poor results following arthroscopic surgery, and open treatment is favored. Specifically, patients with a anteroinferior bone loss or an engaging Hill Sachs lesion (ie, the humeral defect contacts the glenoid rim in flexion abduction and external rotation) should be addressed with open techniques. Osseous deficiency greater than 20% of the anteroinferior glenoid can be treated with open reduction and internal fixation, structural bone grafting, and coracoid bone transfers such as the Bristow-Latarjet. Engaging Hill-Sachs lesions are reconstructed with allograft to restore the humeral surface, arthropasty, or rotational osteotomy. 

The indications for the surgical treatment of posterior instability include failure of non-operative treatment and continued symptomatic instability interfering with activity or sport.  Surgery is contraindicated in voluntary dislocators. There is no consensus procedure of choice for the treatment of posterior shoulder instability. Surgically, the reverse Bankart lesion, capsular laxity, humeral retroversion, and glenoid hypoplasia might be addressed surgically to reduced posterior instability. Open or arthroscopic repair of the reverse Bankart tear and capsular shift are effective. A reverse Hill-Sachs is treated with a structural bone graft to the humeral head or McLaughlin procedure (transfer of the lesser tuberosity to the humeral defect. 

Outcome

The treatment goals for shoulder instability are to restore normal anatomy by repairing anteroinferior labral tears and capsular redundancy, as well as correct osseous defects of the glenoid and humeral head that would lead to recurrent instability. Shoulder instability surgery can be performed arthroscopically or through an open approach. 

Historically, an open Bankart repair was considered the gold standard for the treatment of anterior shoulder instability. The rate of recurrent instability following open Bankart repair ranges from 3% to 9%.^26-28 Open repair, however, has been associated with less favorable functional outcomes, inability to return to preinjury level of activity, incomplete patient satisfaction, and loss of shoulder motion. Notably, Bigliani et al.²⁹ reported that only 63% of throwing athletes were able to return to their preinjury competition level. Consequently, although instability may be low following open repair, the complication following open repair has lead to the investigation of arthroscopic techniques for shoulder stabilization. 

Several prospective studies have compared arthroscopic versus open stabilization procedures in the treatment of acute shoulder instability.^30-32 In these studies, no significant difference was seen in recurrent instability between arthroscopic and open stabilizations.

Several authors have investigated the outcomes of arthroscopic shoulder stabilization versus nonoperative treatment. Wheeler et al²² demonstrated that arthroscopic stabilization following initial anterior shoulder dislocations was 22% compared with a 92% recurrence in non-operatively treated young athletes. Others have reported lower recurrence rates in the range of 11% to 14% following early arthroscopic stabilization.^18,33 More recently, Owens et al reported after long-term follow up that the incidence of recurrent dislocation following arthroscopic stabilization for initial anterior shoulder dislocations was 14.3%, and patients had excellent subjective and objective clinical outcome scores. 

In conclusion, arthroscopic stabilization for primary shoulder dislocations in high-demand young patients reduces recurrence and improves subjective and objective outcomes. While it is possible that a small number of patients may receive a shoulder stabilization procedure unnecessarily, this treatment approach ultimately will significantly reduce recurrent instability in most patients and may avoid more morbid reconstructive procedures associated with recurrent instability. 

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32. Fabbriciani, C.; Milano, G.; Demontis, A.; Fadda, S.; Ziranu, F.; and Mulas, P. D. Arthroscopic versus open treatment of Bankart lesion of the shoulder: a prospective randomized Kirkley, A.; Werstine, R.; Ratjek, A.; and Griffin, S. Prospective randomized clinical trial comparing the effectiveness of immediate arthroscopic stabilization versus immobilization and rehabilitation in first traumatic anterior dislocations of the shoulder: long-term evaluation. Arthroscopy. 2005;21:55-63.