Anterior Glenohumeral Instability

Updated: Sep 20, 2022
Author: Brett D Owens, MD; Chief Editor: Mohit N Gilotra, MD, MS, FAAOS, FAOA 

Overview

Practice Essentials

The term anterior glenohumeral instability refers to a shoulder in which soft tissue or bony insult allows the humeral head to subluxate or dislocate from the glenoid fossa, resulting in symptoms and compromised function of the joint.[1]  Patients typically experience apprehension, recurrent subluxations, and frank dislocations. This pathology limits many activities, especially physical or athletic endeavors requiring overhead motion and external rotation.

The shoulder is the most commonly dislocated joint in the body. Additionally, shoulder dislocation in adolescents has a notorious natural history; one systematic review reported a 47% recurrence rate within 1 year when glenohumeral dislocation was managed nonoperatively.[2]  Excessive deviation of the humeral head on the glenoid can occur in three planes: anterior, posterior, or inferior. As many as 95% of shoulder dislocations are anterior. Anterior dislocations often lead to recurrent anterior glenohumeral instability.[3]  Recurrent dislocation not only is traumatic and disabling but also can result in further soft-tissue damage and progressive bony loss.

Normal shoulders have a certain degree of laxity secondary to minimal bony restraint, which allows the widest range of motion (ROM) of any joint in the body. The result is a tremendous need for competent soft-tissue stability. Traumatic damage leads to laxity in the soft-tissue and bony restraints, and recurrent subluxation and dislocation may ensue. Atraumatic etiologies also exist, but this article focuses on recurrent subluxation and dislocation due to trauma.

Nonoperative and operative therapies both play a role in the treatment of anterior shoulder instability.[4]  Surgical management has evolved, culminating in effective options that achieve stable repair with little restriction of motion. Reports of anterior glenohumeral instability and its many repair methods date back to Hippocrates' treatise On Joints. Hippocrates described the practice of using cautery to cause the capsule to scar and thus tighten around the joint: "[G]rasp the skin at the armpit between the fingers and draw it in the direction towards which the head of the humerus gets dislocated, then pass the cautery right through the skin thus drawn away."

Since Hippocrates' description of capsule repair, a multitude of new techniques have been reported. These repairs can be divided into anatomic and nonanatomic. Anatomic repairs focus on repairing the structure that has been disrupted. Nonanatomic repairs (e.g., Putti-Platt, Magnuson-Stack, and Bristow procedures) attempt to shorten or tighten certain anterior structures. Early in the evolution of capsular repair, loss of motion was considered acceptable and even desirably as an outcome of shoulder stabilization. As new techniques have emerged, stability was achieved without significant compromise in ROM measurements; postoperative ROM restriction is now considered a surgical complication.

In 1923, Bankart described the lesion of traumatic shoulder dislocation in the British Medical Journal, as follows: "The essential lesion is the detachment of the capsule from the fibro-cartilaginous glenoid ligament." He went on to remark that "the only rational treatment is to reattach the fibrous capsule to the glenoid ligament whence it has been torn."[5]  du Toit and Roux described a similar procedure in 1965, using staples.[6]  The Magnuson-Stack procedure and the subsequent Putti-Platt procedure both used the subscapularis to produce a sling effect on the humeral head; both effectively decreased dislocation recurrence, but subsequently decreased ROM.

In 1954, Latarjet proposed the procedure that bears his name, and a very similar operation was later popularized as the Bristow procedure; these operations involve transfer of the tip of the coracoid process with its muscular attachments. A slit in the subscapularis allows the osteotomized coracoid to be attached to the anterior glenoid, providing both a sling effect and a bony block against anterior glenohumeral translation.[7]

Anatomy

The shoulder joint is a simple structure that provides complex function. In addition to the glenohumeral joint, the acromioclavicular, sternoclavicular, and scapulothoracic joints collectively allow for shoulder motion. Stabilization is provided by the following three main players[8] :

  • Bony stabilizers
  • Soft-tissue passive stabilizers
  • Soft-tissue active stabilizers

Bony stabilization

The foolowing are the most important bony stabilizers of the shoulder:

  • Glenoid
  • Humeral head
  • Clavicle

The glenoid fossa provides a shallow socket within which the humeral head articulates. In the average patient, the glenoid face is positioned in slight inclination and retroversion; variation in these angles can increase the risk of instability. Variation in the glenoid height-to-width ratio (the glenoid index) has also been identified as a significant risk factor for instability.[9]  

The actual articulation between the glenoid socket and the humeral head provides little stability itself, because only 25-30% of the humeral head is in contact with the glenoid at any point throughout anatomic ROM. The stability ratio is defined as the force necessary to dislocate the humeral head from the glenoid, divided by compressive force, and is influenced in part by the depth of the glenoid, in addition to the labrum and any chondrolabral or glenoid defects.[10]  

The scapula also plays an important role in shoulder stability, serving as the bony link between the humerus, the clavicle, and the axial skeleton—as well as providing the attachment or origin site for 17 different muscles.

The glenoid, the acromion, and the coracoid process are important scapular landmarks. Anatomic variation in the coracohumeral distance has been shown to be an independent risk factor for shoulder instability, with a 1-mm difference being associated with a 20% increase in the risk of injury.[9]  

Finally, the clavicle articulates with the scapula at the acromioclavicular joint, providing an attachment site for many muscular stabilizers and facilitating shoulder elevation.

Passive soft-tissue stabilization

The following are the most important players for passive soft-tissue stabilization[8] :

  • Glenoid labrum
  • Glenohumeral ligaments
  • Glenohumeral joint capsule

The labrum is a fibrocartilaginous structure that constitutes the margin of the glenoid cavity, deepening the glenoid socket by about 50%.[11]  The flexible labrum also exerts a suction-cup effect on the humeral head using negative intra-articular pressure, and it functions as an anchoring point for the glenohumeral ligaments and the biceps tendon.[12] Labrum injury is often comorbid with traumatic shoulder instability. Cadaveric studies have demonstrated increased laxity in shoulders with independently resected labrums.[13]

The joint capsule extends from the periphery of the glenoid to surround the proximal humerus. Within the anterior capsule are the following three major capsular thickenings:

  • Superior glenohumeral ligament (SGHL)
  • Middle glenohumeral ligament (MGHL)
  • Inferior glenohumeral ligament (IGHL)

The SGHL and MGHL attach proximally at the anterosuperior portion of the glenoid labrum. The IGHL is the key anterior stabilizer of the shoulder, by virtue of its comparatively large size and considerable tensile strength.[14]  The IGHL attaches proximally to the anterior, inferior, and posterior margins of the glenoid labrum; distally, it attaches to the inferior margin of the anatomic neck of the humerus. The IGHL is composed of an anterior band (AIGHL) and a posterior band (PIGHL), which together form a U-shaped “hammock” structure.[15]  

Collectively, the glenohumeral ligaments function to limit lateral rotation of the shoulder. Each of the three ligaments is relied upon for stability, depending on the dynamic position of the arm. Delorme found that the MGHL tightens as the arm is externally rotated or dorsally flexed; if the arm is then abducted, the IGHL becomes the primary stabilizer.[16]  Although recurrent glenohumeral instability is often attributed to injury of the anterior labroligamentous structures (ie, a Bankart lesion of the labrum), humeral avulsion of the glenohumeral ligament (HAGL) may be a less common but clinically relevant cause; the AIGHL is the most commonly injured portion.[17]

Active soft-tissue stabilization

Active soft tissue stabilization of the shoulder is provided by several important muscle groups, including the following[8] :

  • Rotator cuff (RC)
  • Long head of the biceps
  • Subset of the parascapular muscles

The RC is composed of four muscles—supraspinatus, infraspinatus, teres minor, and subscapularis—whose attachments surround the glenohumeral joint. They play a dual role, involved in both joint motion and stability; conservative therapy focuses on strengthening these muscles to prevent recurrent dislocation.

The supraspinatus initiates shoulder abduction and assists the deltoid with further abduction. The infraspinatus provides external rotation and elevation. These two muscles work with the rest of the RC to compress the humeral head in the glenoid throughout ROM. The supraspinatus and the infraspinatus become confluent in their attachment to the greater tuberosity as the posterosuperior rotator cuff. The anterior portion of the supraspinatus is termed the rotator cable, which has been described as the primary load-bearing structure of the supraspinatus; most tears occur here, and disruption in this area has the potential to dramatically alter allowable glenohumeral translation.[18]  

With the infraspinatus, the teres minor works to rotate the shoulder externally, and it compresses the glenohumeral head as it traverses laterally to the inferior greater tuberosity.

The subscapularis is the largest RC muscle, originating from the subscapular fossa of the anterior scapular surface and attaching to the lesser tuberosity of the proximal humerus; it internally rotates and adducts the arm. At 45° of abduction, the subscapularis becomes taut over the anterior joint surface and ascends so that its inferior margin lies at the inferior margin of the glenoid. External rotation additionally increases muscle tautness. Finally, at 90° of abduction, the inferior portion of the subscapularis no longer covers the inferior humeral head. It continues to provide anterior stabilization by remaining taut.

The long head of the biceps originates form the supraglenoid tubercle and exits the joint via the bicipital groove, after which it converges with the short head of the biceps; it provides rotational and translational stability, as well as stability from humeral head depression.[19]  

The deltoid, the pectoralis major, and the latissimus dorsi are important humerothoracic muscles that are involved in shoulder stability, especially as it pertains to the "force couple" in the superior-inferior direction. A force couple is two muscles acting in opposing directions that influence the rotation of a joint in some direction; an injury to one part of the force couple can cause an imbalance and possible instability.[8]  

Two other force couples are important for the shoulder. The transverse plane force couple comprises the action of the subscapularis anteriorly and the pull of the infraspinatus and teres minor posteriorly. The force couple in the coronal plane involves the deltoid superiorly and the rotator cuff muscles (infraspinatus, teres minor, and subscapularis) inferiorly; when balanced, it provides stable glenohumeral abduction.[20]

Pathophysiology

In an unstable shoulder, many findings are possible, occurring alone or in combination; in 1978, Rowe came to the still upheld conclusion that no single lesion is responsible for recurrent dislocation of the traumatized shoulder. The various pathologic lesions broadly include the following:

  • Bankart lesion
  • Anterior glenoid rim damage (“bony Bankart”)
  • Hill-Sachs lesion
  • Glenoid fossa bone loss
  • Capsular redundancy
  • Subscapularis deficiency
  • Attenuation of the capsule and capsular ligaments
  • Humeral avulsion of the IGHL (HAGL and its variants)

Clinical instability in the absence of a pathologic lesion is also possible.

The Bankart lesion—a term describing direct injury to the anterior labrum as the humeral head dislocates anteriorly—is the most common lesion. A review by Owens et al corroborated previously accepted rates of Bankart lesions in 97% of first-time traumatic anterior subluxation imaging.[21] However, injury to the anterior labrum does not usually occur in isolation; the IGHL may undergo deformation, and the anterior glenoid rim may also fracture. Milano et al reported that a bone defect, colloquially called a bony Bankart, occurred in 72% of patients with anterior instability.[22] Bone loss may extend into the glenoid fossa, probably secondary to repeated erosion.

Additionally, the humeral head may be injured via a contrecoup mechanism, resulting in a Hill-Sachs lesion; this is a fracture secondary to impaction of the posterosuperolateral humeral head adjacent to the rotator cuff insertion. Rates of Hill-Sachs lesions are in the range of 7-93%, approaching 100% with recurrent instability.[23]

Combined or bipolar bone loss—from both the glenoid fossa and the humeral head—is a common presentation. One systematic review reported that after both nonoperative and surgical treatment of shoulder instability, bipolar bone loss was associated with higher rates of recurrence.[24] This is in part due to the additive risk of further damage when bipolar bone loss exists; continued instability events can lead to engagement of the Hill-Sachs lesion on the anterior glenoid.

The concept of the “engaging Hill-Sachs” lesion led to the secondary concept of the glenoid track, as described by Yamamoto et al in 2007.[25] The glenoid track is a comparison of 83% of the width of the glenoid minus the width of bone loss; if the Hill-Sachs lesion is wider than the glenoid track, it is considered to be off track. An off-track lesion predisposes a patient not only to recurrent instability but alsoto  failure of a soft-tissue-only repair of a Bankart lesion.

Etiology

The cause of anterior glenohumeral instability can be traumatic or atraumatic, and either mechanism can lead to the loss of balance in the surrounding soft-tissue structure. Traumatic insult most commonly causes anterior dislocation. Posterior shoulder dislocation is often associated with seizure disorders but can also be secondary to traumatic athletic injury.

Atraumatic causes can lead to multidirectional instability; however, these causes are not the focus of this article. Etiologies include repetitive atraumatic injury, Ehlers-Danlos syndrome, Marfan syndrome, congenital absence of the glenoid, and deformities of the proximal humerus.

Epidemiology

Epidemiologic studies using national injury databases have reported the incidence of shoulder dislocation in the United States to be 23.9 per 100,000 person-years, with nearly half occurring during athletic activity in patients in their second or third decade of life.[26]  Young male patients participating in athletics and military service and/or training are the population most at risk. Similar trends have been described internationally.

There are several modifiable and nonmodifiable risk factors that predispose patients to glenohumeral instability.[8] Modifiable risk factors include the following:

  • Shoulder girdle strength
  • Activity modification
  • Shoulder proprioception
  • Occupation
  • Sport participation

Nonmodifiable risk factors include the following:

  • Age at primary instability event
  • Male sex
  • Hyperlaxity
  • Chondrolabral cleft
  • Glenoid dysplasia or version

Age at the time of dislocation is the most important determinant of future recurrence. Recurrences from anterior glenohumeral instability occur most commonly in patients younger than 20 years; reported recurrence rates in such patients range from 70% to 100%.

Prognosis

Outcomes of anterior glenohumeral repair depend first on identification of specific pathology and then on choice of repair. With these key factors addressed, patients can expect a low incidence of complications, good ROM, and stable repair with a low risk of recurrence.[27, 28]

In a systematic review, Chalmers et al critically evaluated eight meta-analyses comparing open and arthroscopic approaches to shoulder stabilization with labral repair and capsulorrhaphy.[29]  Two pre-2007 meta-analyses concluded that open stabilization provided lower recurrence rates; three 2007 meta-analyses were discordant; and three post-2008 meta-analyses concluded that the two approaches provided equivalent results. Two meta-analyses were judged to have major flaws.[29]  The meta-analysis independently selected by four authors as providing the highest-quality evidence found no difference in recurrence rates between the two approaches.

Bliven et al reviewed eight studies (N = 795) to compare the outcomes of Latarjet repair (open only) with those of Bankart repair (open in six studies and arthroscopic in two) in patients with recurrent traumatic anterior shoulder instability.[30]  They found the Latarjet procedure to be associated with a lower recurrence rate, better outcomes as reported by patients, and less restriction of external-rotation motion than the Bankart repair.

Potential comorbid injuries associated with primary anterior glenohumeral dislocation include rotator cuff tear, greater tuberosity fracture, and neurologic deficit. These injuries may occur alone or in combination and are more common in patients older than 60 years.[31, 32]

 

Presentation

History

Anterior dislocation of the glenohumeral joint occurs with the arm in a forward flexed, abducted, and externally rotated position. Children presenting with a dislocated shoulder may relate a couple of possible mechanisms; most commonly, the child falls on the outstretched hand, forcing the arm into abduction, levering the humeral head out of the glenoid cavity. In adults, mechanisms include contact sports, after a fall from a height, fights, and motor vehicle accidents. Patients can experience a range of injury and most commonly report traumatic subluxation without frank dislocation.

According to data from the National Collegiate Athletic Association (NCAA), sports commonly implicated include football, hockey, wrestling, and other contact events.[33]

Physical Examination

Physical examination begins with inspection of the shoulder, especially as it compares to the asymptomatic side. Any atrophy of the biceps, supraspinatus, infraspinatus, or deltoid must be noted. Injury to the axillary or suprascapular nerves may be caused by previous dislocation and can be perceived as asymmetry of associated muscles on exam.[8]  Gross deformity can also suggest a dislocation and its direction; however, depending on the clinical setting, a dislocation may have been reduced previously. Both shoulders should be palpated, with a focus on tenderness, deformity, and crepitus. Tenderness at the lateral shoulder is frequently reported with Hill-Sachs lesion secondary to dislocation.

Passive and active range of motion (ROM) should then be assessed, including the following:

  • Forward flexion
  • Abduction
  • External rotation in adduction and 90º of abduction
  • Internal rotation behind the back and in 90º of abduction

Patients with a recent traumatic dislocation event often will have decreased ROM secondary to muscle guarding, inflammation, or pain, whereas  patients with chronic or atraumatic instability may demonstrate normal ROM or even hypermobility.

It is important to differentiate laxity from instability. Laxity in the shoulder is defined as the ability of the humeral head to be passively translated on the glenoid fossa. Patients presenting with shoulder instability frequently have generalized ligamentous laxity. The Beighton Hypermobility Score is a useful adjunct diagnostic tool.[34] In this tool, one point is given for each of the following:

  • Demonstrated hypermobility of the small-finger metacarpophalangeal (MCP) joint past 90º
  • Ability to connect the thumb and the volar forearm
  • Hyperextension at the elbow past 10º
  • Hyperextension at the knee past 10º
  • Ability to place both hands flat on the ground with knees extended

Because the first four are assessed bilaterally, the highest possible score is 9. Generalized laxity is defined as a score of 4 or higher.[34]  

Multiple examination tests have been described to assess shoulder-specific laxity, including the following[8] :

  • Anterior and posterior drawer tests
  • Load and shift test
  • Sulcus test (sulcus sign)
  • Gagey hyperabduction test 

The anterior drawer test is performed with the patient supine while the examiner holds the upper arm in 80-120º of abduction, 0-20º of forward flexion, and 0-30º of external rotation; in this position, the examiner then provides an anterior-directed force.[35]  The posterior drawer test uses a similar position but the examiner frames the patient’s shoulder with the thumb placed anteriorly and the fingers placed posteriorly while applying a posterior-directed force through the humeral head.

The load and shift test can be performed with the patient either seated or supine as the arm is held in slight abduction, 20º of forward flexion, and neutral rotation; while applying an axial load to the humeral head, the examiner simultaneously attempts to translate the humeral head anteriorly and posteriorly.[8]  Performing the load and shift test with the patient supine may help stabilize the scapula while allowing the patient to remain relaxed. The Gerber and Ganz classification grades translation from grade I (translation of the head to the glenoid rim) to grade III (translation over the glenoid rim without spontaneous reduction) for the anterior and posterior drawer tests and the load and shift test.

The sulcus test (sulcus sign) is performed on a seated patient with the arm adducted at the side in both neutral and external rotation; the test is positive if an inferior force results in inferior translation of the humeral head and a resulting space or sulcus between the acromion and the proximal humeral head.

The Gagey hyperabduction test is performed on a seated patient; the examiner uses one hand to stabilize the scapula and provide an inferior-directed force and the other hand to abduct the affected arm until the scapula is felt to begin rotation.[36]  A positive test is abduction to over 105º before scapular rotation.

As part of a full physical examination, shoulder strength should also be assessed, with a specific focus placed on each of the rotator cuff muscles in isolation.[8]  Briefly, the supraspinatus is evaluated with supraspinatus isolation (the Jobe test). The infraspinatus is evaluated with resisted external rotation with the elbow at the patient’s side. The teres minor is evaluated with the Hornblower test. Finally, the subscapularis can be evaluated with either the liftoff test, with the patient’s hand starting on the lumbar spine, or the belly-press test.

Impingement signs must also be evaluated because as many as 10% of patients experience impingement after dislocation. It is important to evaluate for the Hawkins sign and perform the Neer impingement test.

Provocative examination maneuvers can also assist the clinician in diagnosing and assessing anterior shoulder instability. The key finding in anterior glenohumeral instability is a positive apprehension test. The arm is placed in abduction, extension, and external rotation while being stressed in anterior translation. If the patient becomes apprehensive and reports pain, this is considered a positive finding. It is important to note that pain alone does not constitute a positive apprehension test: The patient must report apprehension.

The relocation test involves placing the shoulder in the position of apprehension and applying a posterior-directed force to the humeral head. The result is considered positive if this relieves the patient's apprehension.

The anterior release (surprise) test is also sensitive and specific for clinically diagnosing anterior shoulder instability. This test can be thought of as the last step of the apprehension test, in which the posterior-directed force is removed, and the patient once again reports apprehension or the feeling of impending dislocation.[37, 38]

 

Workup

Radiography

Radiologic study of the dislocated or subluxated shoulder should include a minimum of three views: anteroposterior (AP) or true AP (Grashey) view, scapulolateral view (scapular Y), and axillary lateral view. This combination of views provides the best evaluation of the bony structures. Although frequently only soft-tissue injury is present, bony pathology is present in 55% of traumatic dislocations, and plain radiographs are a simple and low-cost screening tool for detecting significant glenoid and humeral bony defects.

True anteroposterior (AP)—Grashey view

This view is obtained by placing the posterior surface of the scapula flat onto the radiography film. This results in a view that is 45° oblique to traditional shoulder AP radiography.

A successful exposure demonstrates the glenohumeral joint space, superoinferior head subluxation, joint congruity, joint degeneration, and other articular abnormalities. Disadvantages to this view exist, including anterior and posterior glenoid overlap, which can obscure Bankart lesions; this overlap may be exacerbated by inadequate radiographic technique. Increased soft-tissue overlap as compared with a traditional AP view lessens the quality of bony detail. Jankauskas et al found this view to be 100% specific but not sensitive (54-65%) for glenoid bone defects.[39]

Scapular Y view 

The scapular Y view is obtained by aiming the x-ray beam longitudinally down the axis of the scapular spine (see the image below) to obtain a true lateral view of the glenohumeral joint. The humeral head lies directly over the glenoid fossa; if the shoulder has been dislocated anteriorly, the humeral head will be seen anterior to the glenoid fossa. The Y shape is formed by the projection of the acromion, the scapular body, and the coracoid from the longitudinal axis.

Scapular Y-view of normal shoulder. Courtesy of Wi Scapular Y-view of normal shoulder. Courtesy of Wikimedia Commons (Mikael Häggström) [https://commons.wikimedia.org/wiki/File:Y-projection_X-ray_of_a_normal_shoulder.jpg].
Y-view radiograph of right shoulder shows anterior Y-view radiograph of right shoulder shows anterior dislocation of humeral head relative to glenoid fossa.

This view may be adequate for evaluating dislocations, but it should never replace the axillary view, which is the most sensitive for detecting subluxations. Like the true AP view, it is a poor choice for evaluating glenoid rim fractures.

Axillary view 

The axillary lateral view has many variations. As described originally by Lawrence in 1915, it was obtained with the patient supine, the arm abducted to 70-90°, and the x-ray beam aimed from inferior to superior with 15-30° of medial angulation, depending on the amount of abduction. The resulting radiograph allows detection of AP subluxation/dislocation and anterior or posterior glenoid rim fractures.

Axillary view of shoulder with anterior instabilit Axillary view of shoulder with anterior instability.

One alternative is the modified axillary lateral (or Velpeau) view, which may be a good choice if abduction is poorly tolerated because of pain. In this modification, the arm can be maintained in adduction within a sling, and either the patient leans back 20-30º or a wedge with similar angulation is placed behind the patient’s back.

Another variation is the West Point view, which is most helpful in identifying large glenoid defects and humeral head subluxation.[40]  It places the patient prone with the arm abducted to 90° and hanging over the edge of the table. The x-ray beam is directed 25° medially and anteriorly. This position improves visualization of the anteroinferior glenoid rim. West Point axillary views are the most sensitive for finding osseous glenoid fractures.[41]

Stryker-Notch view

The Stryker-Notch view was developed to allow visualization of Hill-Sachs lesions of the posterolateral humeral head. It is obtained with the patient supine. The hand is placed on top of the head with the elbow flexed. The x-ray beam is directed from anterior to posterior with a 10° cephalic angulation. It provides good detail of the posterolateral margin of the humeral head.

Humeral internal and external rotation views

Internal and external rotation views provide oblique visualization of the shoulder joint, with the humeral head overlapping the glenoid rim.

The advantage of these views is that they obtain excellent osseous detail of the greater tuberosity, scapula, clavicle, upper ribs, and soft tissues. The high-quality bony detail is the result of the low density of the surrounding soft tissue. Internal rotation of the arm in the AP view projects the lesser tuberosity medially and the posterolateral aspect laterally, providing a good view of Hill-Sachs lesions. These views are of little value in detecting anterior or posterior dislocation/subluxation.

Computed Tomography and Magnetic Resonance Imaging

For most authors, magnetic resonance imaging (MRI) is the imaging modality of choice for soft-tissue injury.[42]  It has been shown to be 91% sensitive in detecting capsulolabral lesions in the early postdislocation period. Specifically, it provides comprehensive visualization of important soft-tissue structures that may be injured in anterior instability, including the anterior labrum, the anterior capsule, and the anterior inferior glenohumeral ligament.

Martins e Souza et al evaluated the accuracy of conventional MRI in determining the severity of glenoid bone loss in 36 patients with anterior shoulder dislocation by comparing results obtained by using conventional MRI with results from arthroscopic measurements.[43]  They found that interreader and intrareader correlations of MRI-derived measurements of glenoid bone loss were excellent and that the first and second observers' measurements showed strong and moderate interreader correlation, respectively, with arthroscopic measurements.

Magnetic resonance arthrography uses intra-articular contrast to distend the joint space, allowing space to visualize details of damage to the glenohumeral ligaments and labrum. There is continued debate over whether this additional imaging modality is necessary if an optimized MRI has been obtained.

Computed tomography (CT) is of increasing importance in the assessment of bone defects; it is currently considered the gold standard diagnostic tool for identifying bony defects and quantifying bone loss after recurrent anterior instability.[44]  In a study of 70 patients with traumatic anterior glenohumeral instability, Delage Royle et al found that regular radiographs had suboptimal sensitivity, specificity, and reliability for evaluation of glenoid and humeral bone loss.[45] They recommended that CT be considered in the treatment algorithm for accurate quantification of bone loss.

An important use of these advanced imaging modalities is determination of the extent of glenoid bone loss, which is essential for clinical decision-making. There are many measuring methods that use MRI or CT; they can be broadly categorized into two groups: (1) width techniques and (2) best-fit circle techniques.[46]

Width methods include the following:

  • Glenoid rim distance
  • Glenoid index
  • Width-length ratio
  • West Point measurement

Best-fit circle techniques include the following[8] :

  • Pico method
  • Sugaya method
  • Dumont arc angle method
  • MRI methods

No measurement method has yet been established in the literature as a gold standard; accordingly, the choice of method should be based on available quality imaging and provider preference. Measurements of humeral bone loss, or Hill-Sachs defects, have been less extensively studied but include the use of plain radiographs, MRI, and CT.

 

Treatment

Approach Considerations

Indications and contraindications for surgery

At present, there is no firm consensus on the optimal treatment strategy for first-time glenohumeral dislocation, though early surgical stabilization is increasingly being preferred in view of the high failure rates and decreased cost-effectiveness of nonoperative management alone.[47] Nonmodifiable risk factors attributed to a patient must be considered as well.

The indications for surgical repair in a patient with anterior glenohumeral instability depend on the patient presentation and the individual surgeon. A shoulder in which conservative therapy has failed or any shoulder that has been rendered unstable may undergo repair.

Frequently, determination of appropriate treatment may be facilitated by classifying patients into one of the following two categories:

  • Young patients with heavy physical demands - These patients may forgo conservative therapy and proceed to immediate surgical repair; this recommendation is based on the high recurrence rate and the patient's desire to return to activity
  • Older patients with lesser physical demands - These patients may try conservative therapy before assuming the risks of surgical repair; they have a lower likelihood of recurrence and may not require any treatment beyond conservative therapy

Surgery is also indicated if the patient is symptomatic with activities of daily living (ADLs) or if overhead stability is specifically needed. The patient must understand, however, that overhead stability cannot be guaranteed postoperatively.

Surgical repair is relatively contraindicated in older patients with low physical demands, who have little chance of recurrence. Conservative therapy, including physical therapy to strengthen the rotator cuff, is indicated in preference to exposing these patients to the risks of operation. Patients who have been asymptomatic in their ADLs also need not be exposed to the risks of surgery. These patients are best monitored for any recurrent dislocations.

A contraindication exists in the case of multidirectional instability of the shoulder. In these atraumatic dislocations, patients are able to dislocate and relocate the shoulder voluntarily. Predisposing factors include psychiatric dislocations, laxity due to repetitive injury (as in competitive swimmers), and congenital collagen abnormalities (eg, Ehlers-Danlos syndrome and Marfan disease). The history and physical examination must be used to identify these patients. If these patients are treated as if they have unidirectional dislocations, operative therapy may fail. The amount of inferior capsular redundancy in multidirectional instability requires an operative procedure addressing the possibility of future inferior instability.

There is considerable room for improvement in the management of anterior glenohumeral instability, especially with arthroscopic treatment. Studies have shown that any type of shoulder instability can be treated arthroscopically. Advances in techniques and equipment have made treatment somewhat easier. The rate of recurrence remains higher after arthroscopic treatment than after open repair. Open repairs continue to provide good functional results. Postoperative range of motion (ROM) of the shoulder in patients who undergo open repair may not reach that observed in patients with arthroscopically repaired shoulders.

Once the decision has been made to proceed operatively, the next major question is the choice of procedure. Major considerations include patient profile and the amount of glenohumeral bone loss. Balg and Boileau developed a scoring system, the Instability Severity Index, to determine the likelihood of arthroscopic surgical failure.[48] They associated scores higher than 6 with a high risk of failure; however, subsequent studies have suggested that the threshold for failure may be much lower (ie, >2).[49]

Traditional recommendations have proposed arthroscopic repair for glenolabral injuries with less than 20% bone loss and procedures with anterior glenoid bony augmentation for cases where bone loss exceeds 20-25%.[8] However, this threshold may be lowered to 15% on the basis of more recent literature.

Additionally, if a patient has a Hill-Sachs lesion that is considered on track, it can be left alone and managed as above. If it is instead considered off track with a subcritical bony defect, it should be managed with arthroscopic Bankart repair and remplissage (filling in). If it is off track with glenoid bone loss greater than 15-20%, it should be managed with a Latarjet procedure or anterior glenoid bone block reconstruction. Multicenter randomized controlled trials have been initiated with the aim of investigating management of patients who fall in the middle of that spectrum.

Nonoperative Therapy

Nonoperative management of anterior glenohumeral instability must be considered. This consists of a period of shoulder immobilization. Subsequent physical therapy reestablishes ROM and strengthens the rotator cuff. As discussed above, age and other nonmodifiable risk factors are important to consider.

More important, it seems, is the physical therapy program. This should focus on isotonic strengthening before isokinetic strengthening. The first musculature to rehabilitate consists of the periscapular muscles: the serratus anterior, the trapezius, and the rhomboids. The deltoids follow, and finally, strengthening should focus on the rotator cuff.

No substantial evidence supports physical therapy as a treatment for high-risk patients. Thus, conservative management is reserved for persons with first-time dislocations who are older than 20-25 years and are sedentary.

Surgical Therapy

Indications for repairing an anteriorly unstable shoulder are not obvious. The patient and surgeon must consider the possible outcomes in the light of the patient's activity level and the most probable natural history of the individual's instability. At times, forgoing conservative therapy and proceeding directly to surgical repair may be appropriate.

In the case of a patient who has experienced dislocation fewer than three times, attempting an arthroscopic repair is reasonable. Arthroscopic repair is associated with a lower incidence of shoulder stiffness but has been shown to have a higher risk of recurrence.

Persons with truly recurrent dislocations have dislocated their shoulder more than two or three times. In these cases, patients may want to risk the possibility of stiffness in return for the stability created by a Bankart repair.

Many options exist for the surgical repair of anterior glenohumeral instability. Arthroscopy provides the least invasive repair. Open shoulder repairs include the Putti-Platt, Bristow (or Bristow-Latarjet), Magnuson-Stack, inferior capsular shift, Eden-Hybbinette, Trillat, and Bankart procedures.[50]  Arthroscopic repair has potential advantages, including improved cosmesis, less postoperative pain, shorter operating time, decreased blood loss, better preservation of external rotation, and avoidance of subscapularis-related complications.[51, 52]  Arthroscopic Bankart repair is the most commonly used technique for treatment of athletes with anterior shoulder instability.[8]

One study, reviewing data from the American Board of Orthopaedic Surgery (ABOS), noted that the use of open repair has been declining and that there has been a trend toward arthroscopic Bankart repair.[53]  This study found the most common complications to be nerve palsy/injury and recurrent dislocation. The rate of nerve injury was 2.2% in the open group, compared with 0.3% in the arthroscopic group; the dislocation rate was 1.2% with open stabilization, compared with 0.4% arthroscopically.

Intraoperatively, arthroscopy provides better visualization of the joint. Although recurrence rates in persons with first-time dislocations have been reported to be as low as 5%, subsequent literature has suggested recurrence rates rivaling those noted with open Bankart repairs. In addition, the operative procedure does require significant training.

In a retrospective cohort study that included 364 shoulders), Gerber et al investigated long-term (≥6 y) outcomes of arthroscopic Bankart repair versus open Latarjet repair for recurrent anterior shoulder instability.[54] Arthroscopic Bankart repair was found to be inferior, with 41.7% recurrence of instability or apprehension post Bankart, compared with only 11% post Latarjet.[54]  Secondary outcome measures (patient satisfaction, survivorship, and operative revision) similarly favored the Latarjet procedure, and the difference increased significantly in parallel with increased follow-up time.

Proper patient selection has led to good outcomes in arthroscopically repaired shoulders.[55]  Good candidates for arthroscopic repair are patients with the following:

  • Discrete Bankart lesion
  • Well-developed inferior glenohumeral ligament (IGHL)
  • No significant capsular laxity
  • No intraligamentous injury
  • No concomitant intra-articular pathology
  • Unidirectional instability

Patients who require open repair are those with the following:

  • Bone loss
  • Capsular laxity
  • Poor tissue quality

Preparation for surgery

Several concerns are important preoperatively. The most significant of these is that anterior shoulder instability must be confirmed. The shoulder should be examined again after anesthesia is induced. If the shoulder is found to have multidirectional instability, the operative plan should be canceled or revised.

Operative details

Arthroscopic Bankart procedure

Arthroscopic repair may be either intra- or extra-articular. Extra-articular repair is indicated primarily for labral tears; damage that is more extensive requires an intra-articular repair.

The arthroscopic repair can be performed with the patient in either the lateral recumbent position or the beach-chair position. It should be kept in mind that the lateral position has been associated with traction neurapraxia and allows less joint motion. Recurrent rates may be less with lateral position.[56] The beach-chair position is convenient if a conversion to an open repair is anticipated.

There are several keys to a successful arthroscopic Bankart repair, including the following:

  • Appropriate patient selection
  • Proper mobilization of capsulolabral tissues
  • Repair of the tissue to the edge of the articular surface (not the glenoid neck)
  • Identification and treatment of capsulolabral injury

Preoperative radiography helps determine the presence of a bony Bankart lesion.

The arthroscopic procedure for a soft Bankart lesion also starts with examination under anesthesia. The patient may be in the lateral recumbent or beach-chair position. Access to the joint starts with a posterolateral glenohumeral portal for viewing the joint. A thorough examination is performed before an anterior working portal is made lateral to the coracoid.

The edge of the glenoid articular cartilage is abraded. The capsulolabral complex is dissected and then grasped and advanced over the abraded bone. Anterior reconstruction is then performed with suture anchors and plication of the loose anterior capsule into the labral repair.[57, 58] The most inferior suture is placed first, allowing superior sutures to further tighten the capsuloligamentous complex. The sutures are tightened with the shoulder in internal rotation. ROM can be examined intra-articularly, and the incisions are closed.

Bone graft augmentation may be a beneficial adjunct to arthroscopic Bankart repair in patients who have recurrent anterior shoulder instability with glenoid bone loss.[59]

Open Bankart procedure

Although the procedure has evolved through the years, the open Bankart repair has remained essentially unchanged from the original description by Rowe in 1978.

First, the patient's shoulder is examined under anesthesia to ensure that the patient truly has purely anterior instability and thus can benefit from a Bankart repair. An incision is made from the coracoid process inferiorly to the axilla. The deltopectoral groove is dissected, exposing the cephalic vein and retracting it. The coracoid process is osteotomized, allowing the coracobrachialis and short head of the biceps to retract inferiorly.

External rotation of the arm exposes the subscapularis. The circumflex vessels at the inferior border of the muscle can be ligated. The subscapularis is then separated from the capsule. With the arm fully externally rotated, a vertical incision is made in the subscapularis just lateral to the glenoid rim. This provides a large flap for repair of the capsule with adequate external rotation postoperatively.

With the humeral head retracted posterolaterally, the rim of the glenoid and the anterior neck of the scapula are freshened by using a small osteotome. Three holes are made in the anterior glenoid rim, located at 1, 3, and 5 o'clock on the right glenoid and at 11, 9, and 7 o'clock on the left glenoid.

A double-0 suture is passed through each hole and then through the edge of the lateral capsular flap. This is tied while the capsular flap is held to the freshened anterior glenoid rim. With the same suture ends, the medial capsular flap is then tied down on top of the lateral one. This reinforces the capsule at the rim of the glenoid. External rotation is then checked; it should extend easily to 25-30° beyond neutral.

Closure is achieved by returning the tissues to their anatomic positions. The subscapularis is sutured to the lesser tuberosity and secured. Thus, the muscle is not shortened, overlapped, or transplanted, as is the case in other techniques. The coracoid is anchored in place with 0 suture at its base. No separation of the coracoid has been described with the use of suture to anchor it.

Arthroscopic Latarjet procedure

The arthroscopic Latarjet procedure appears to be an effective means of treating off-track Hill-Sachs lesions, restoring them to an on-track state. In a study by Plath et al, a mean persisting enlargement of the glenoid arc of 14% beyond native dimensions remained at a mean of 23 months after this procedure.[60]

Ranne et al reported a modification of the arthroscopic Latarjet procedure for treating anterior glenohumeral instability, in which the detached coracoid was exteriorized through the anteroinferior portal for drilling and shaping.[61]  The 10 patients with severe anterior glenohumeral instability who were treated with this technique had only mild-to-moderate postoperative pain, with no postoperative infections or recurrent dislocations. In terms of safety, the operation was found to be comparable to other operations on the coracoid process in the proximity of the brachial plexus.

A retrospective cohort study by Ali et al found the clinical and radiographic outcomes of the arthroscopic Latarjet procedure to be similar to those of the equivalent open procedure.[62]

Open Latarjet procedure

The open Latarjet procedure is being increasingly utilized as a solution to anterior glenohumeral instability due to significant glenoid bone deficiencies greater than 21%, for which the failure rate of arthroscopic Bankart repair increases significantly.[63, 64, 65] This technique involves splitting the subscapularis to attach a parallel-positioned coracoid process onto the exposed glenoid by using two 3.5- to 4.5-mm screws, as described by Edwards and Walch.[66]

The open Latarjet procedure is reported to prevent recurrent instability in 99% of correctly selected patients.[67]  However, there are several drawbacks to the procedure that may result in complications, such as postoperative stiffness and increased loss of motion. There is also an increased concern for nerve injury.

Reduction of complications

There are several intraoperative details that a surgeon should be aware of to reduce the risk of postoperative complications. For example, incorrect positioning of the coracoid process may result in a lateral overhang, which can lead to rapid bone degenerative joint disease.[68]  Additionally, overtightening of the screws may cause coracoid fractures; this can be prevented by tightening the screws with the two-finger technique. Complications and postoperative rehabilitation can be minimized by employing proper surgical technique. 

Postoperative Care

Postoperatively, the shoulder is kept in an arm sling for 3-4 weeks. The shoulder may be internally rotated and flexed for hygiene maintenance, but external rotation is prohibited.

After 4 weeks, full active flexion is encouraged and assisted with physical therapy. At 6 weeks, internal and external rotation of the shoulder is begun by using 5-lb (~2.25-kg) and 10-lb (~4.5-kg) weights. At 3 months, full and unrestricted weightlifting is allowed. Competitive throwers should be restricted from unrestricted athletics for 6 months.

At 3 months, the patient should have regained 70% of external rotation and elevation of the shoulder. At 6 months, 75-100% of normal motion and strength may be observed.

Complications

Successful repair of anterior glenohumeral instability is extremely rewarding and can render a patient fully functional within months. However, as in any surgical procedure, complications are possible. Unsuccessful surgery in this case can be difficult to salvage.

The most commonly reported complication of open Bankart repair is persistent instability.[63]  Reported rates of recurrent instability range from 3% to 50%. The cause of failure should be determined.

The most common adverse effect of anterior instability is loss of motion. Frequently, decreased external rotation of the humerus is desired to prevent recurrent dislocation; thus, the loss of motion is not reported as a complication. Complications of decreasing the normal shoulder ROM can be serious. In athletes, the late cocking position is disabled, thus decreasing the velocity of their throw. More extensive reductions in external rotation can cause posterior translation of the humeral head.

Iordens and Lieshout found that Putti-Platt repairs in 51 patients resulted in tight anterior structures, which led to glenohumeral arthritis.[69]  This procedure is not the only repair that may result in tight anterior structures: The classic Bankart repair has also been shown to cause limitation of motion and, thus, clinical and radiographic arthritic changes. How much limitation in motion is required to cause late degenerative arthrosis remains to be determined. Studies to date have suggested that small limitations do not cause significant degeneration.

Excessively tight anterior capsules must be addressed to prevent premature arthritic changes. The subscapularis can be released and sutured back into place with the arm externally rotated to the desired position. For greater restrictions, requiring more than 20° of correction, the subscapularis is dissected in the coronal plane, creating a superficial and deep layer. The medial edge of the deep layer of the subscapularis can be sutured to the lateral edge of the superficial layer.

An incorrect diagnosis prior to surgery undoubtedly leads to failure. This can occur when atraumatic multidirectional shoulder instability is confused with traumatic unidirectional anterior instability. In the case of the former, an inferior capsular shift is in order, whereas for the latter, an open or arthroscopic Bankart repair is indicated.

Voluntary instability is a contraindication for any surgical repair mentioned above. These patients can dislocate their shoulders using muscular contractions or arm positioning. A study by Rowe found that most people who dislocate their shoulders voluntarily have "significant psychiatric histories." Nonoperative treatment is necessary in these patients.

Nonanatomic repairs have been shown to result in higher postoperative instability rates. In the original Bankart repair, the anterior glenoid is essentially reconstructed to its original anatomic shape. Procedures that fail to reconstruct the anterior glenoid have been shown to fail more frequently.

Bony Bankart lesions, if large enough, leave a glenoid fossa that lacks concavity. Defects involving greater than 20% of the articular surface must be addressed. Bony lesions involving less than 20% of the glenoid can be resected with the capsulolabral mechanism reattached to the remaining anterior glenoid.

One study assessed the factors associated with the presence, size, and type of glenoid bone defect in patients with anterior shoulder instability.[66]  Computed tomography (CT) revealed a glenoid bone defect in 72% of the 161 patients. The defect was significantly associated with recurrent dislocation, increasing number of dislocations, timing from first dislocation, and manual work; a critical defect was associated with number of dislocations and age at first location; and bony Bankart lesion was associated with male sex and age at first location.

Osteochondral defects of the humeral head may predispose a shoulder to continued instability. A Hill-Sachs lesion alone infrequently causes instability, but when it is coupled with a Bankart lesion, it creates an easily subluxable or dislocated shoulder. Preoperative CT of the Hill-Sachs lesion helps determine the need for repair. The humeral lesion can be prevented from perching on the anterior glenoid by imbricating the anterior capsule and thereby decreasing external rotation.

Other methods of filling in a Hill-Sachs defect have been described, including transfer of the infraspinatus with a portion of greater tuberosity, humeral osteotomy, and humeral hemiarthroplasty or osteochondral allograft for defects involving more than 40% of the head's articular surface.[70, 71]

Further treatment using so-called remplissage, or filling in, of the Hill-Sachs lesion defect with rotator cuff tendon has been studied. A study by Nourissat et al found no significant statistical difference in ROM between patients treated with arthroscopic Bankart repair alone and those treated with Bankart repair and remplissage.[72]  The recurrence rates were identical in the two groups, and one third of patients experienced posterosuperior pain.

Another cause of surgical failure is rupture of the subscapularis. Patients may present after a traumatic event or with persistent postoperative pain, weakness, or continued instability. Physical examination reveals increased external rotation and positive liftoff test results. Magnetic resonance imaging (MRI) may be helpful in confirming this complication. Operative repair includes mobilization of the tendon, which frequently retracts underneath the conjoined, and reattachment to its insertion.

Hardware placed in or around the glenohumeral joint can always cause complications. Loosening and resulting failure have been shown to occur at any time point after surgery. Zuckerman found that the most common culprits were screws or staples that were placed for a coracoid transfer or anterior capsular plication; most of these failures necessitate reoperation.[73]  Chondral damage was found in 41% in Zuckerman's report.

Long-Term Monitoring

Follow-up care can be scheduled on an annual basis after patients have returned to full activity and strength. At these visits, any symptoms of subluxation or dislocation should be explored. Shoulder ROM, strength, and stability are examined, and a radiographic examination is also performed.