Posterior Glenohumeral Instability 

Updated: Jun 29, 2020
Author: John P Salvo, Jr, MD, MS; Chief Editor: S Ashfaq Hasan, MD 

Overview

Practice Essentials

Although the concept of anterior shoulder instability has been described in the medical literature since the time of Hippocrates, the recognition of posterior instability of the glenohumeral joint has been much more recent. Sir Astley Cooper is credited with the first medical description of a posterior shoulder dislocation, in 1822.[1]  He later described the "dislocation of the os humeri upon the dorsum scapula" as "an accident which cannot be mistaken."[2]

Since Cooper's time, numerous articles have gradually raised physician awareness of this condition. In 1952, Harrison McLaughlin defined posterior dislocation as a "diagnostic trap," and others have used equally foreboding descriptions.[3]  Even today, the diagnosis of posterior shoulder dislocation continues to be missed or diagnosed late, after the patient has undergone unsuccessful and often painful therapy for adhesive capsulitis.

Despite the supposed diagnostic difficulty spoken of even today for posterior shoulder dislocations, orthopedic history would indicate otherwise. In 1855 (40 years before the development of radiographs), the French surgeon Joseph Malgaigne published a paper that detailed three of his own patients (and 34 from the literature) that had been diagnosed purely on the basis of physical examination.[4, 5]

McLaughlin also stated that "the clinical diagnosis is clear-cut and unmistakable, but only when the posterior subluxation is suspected."[6]  It also might be said that knowledge of a particular diagnosis statistically increases the likelihood of the clinician making that diagnosis.

In 1949, Wilson and McKeever reported on 11 patients with posterior shoulder dislocations.[7]  Seven of the injuries occurred as a result of trauma, three were due to "epileptic convulsions," and one was due to electrocution. Key clinical findings regarding posterior shoulder dislocations were highlighted by these authors. These included the following:

  • Prominent coracoid process and anterior acromion
  • Flattening of the deltoid
  • Inability to fully supinate the forearm while the elbow is completely extended

For some acute dislocations, Wilson and McKeever recommended that a Velpeau bandage be applied with the patient's shoulder fully internally rotated and with the forearm lying across the small of the patient's back (a position now commonly used at the beginning of the liftoff test for subscapularis function).

Posterior glenohumeral instability is much less common than anterior instability. However, the condition has been recognized with increased frequency; this may be due to improved awareness of the entity, an increasingly athletic population, or both. In early reports of posterior instability, the terminology of instability was confusing, and chronic locked posterior dislocations were often combined with recurrent instabilities.

Each of these conditions has provided physicians with a dilemma not only in diagnosis but also in formulating an ideal treatment plan. The symptoms of posterior instability may mimic those of other disorders, and because complete dislocation does not always occur, the diagnosis cannot be confirmed readily with radiographs.

Advances in arthroscopic techniques hold interesting potential for the management of posterior instability.[8]  Long-term studies, however, are not yet available. Another area of interest has been thermal capsulorrhaphy for instability of the shoulder.[9, 10]  Many authors have described techniques for arthroscopic capsular shrinkage procedures for shoulder instability; however, no outcome studies are available yet for the treatment of isolated posterior instability. This approach may hold promise as an isolated procedure or in combination with other arthroscopic techniques. Short-term results have been encouraging, but longer-term follow-up and published, peer-reviewed studies are required.

The purpose of this article is to review current knowledge about the diagnosis, classification, and treatment of posterior glenohumeral instability.[11]

For patient education resources, see the Dislocated Shoulder Directory.

Anatomy

The anatomy relevant to surgical treatment for posterior shoulder instability is related to the posterior approach to the glenohumeral joint. Two general posterior approaches to the glenohumeral joint have been described.

In 1944, Rowe and Yee presented a posterior approach to the shoulder using a linear incision over the entire length of the scapular spine, extending to the posterior corner of the acromion.[12] The origin of the deltoid on the scapular spine is identified and detached from lateral to medial. The interval between the infraspinatus and the teres minor is defined and retracted to expose the posterior aspect of the joint capsule.

In 1993, Wirth et al described the posterior deltoid-splitting approach to the shoulder.[13] Their technique allows preservation of the deltoid origin from the scapular spine and posterior acromion. (In more traditional posterior approaches to the shoulder joint, part or all of the origin of the deltoid is detached.) This approach therefore maintains the strength and function of the posterior deltoid.

Several structures are at risk during the posterior dissection of the shoulder. The axillary nerve runs through the quadrilateral space beneath the teres minor and can be injured if the interval between the infraspinatus and the teres minor is not critically defined. The suprascapular nerve passes around the base of the spine of the scapula as it runs from the supraspinatus fossa to the infraspinatus fossa. The infraspinatus must not be retracted forcefully too far medially during the approach, because a neurapraxia may result from stretching the nerve around the unyielding lateral edge of the scapular spine.

The posterior circumflex humeral artery runs with the axillary nerve in the quadrilateral space beneath the inferior border of the teres minor muscle. Damage to this artery leads to hemorrhaging that is difficult to control; injury to the artery can be avoided by staying in the correct intermuscular plane.

Pathophysiology

Posterior glenohumeral instability can be associated with several anatomic conditions. Bony anatomic deformities that have been implicated include increased humeral retroversion, glenoid retroversion, and glenoid hypoplasia.[7, 14, 15] When the bony anatomy is normal, the pathoanatomy often is attributed to the following:

  • Excessive capsular laxity (see the image below)
  • Loss of integrity of the capsuloligamentous rotator interval (coracohumeral and superior glenohumeral ligaments) [16, 17, 18]
  • Injury to the superior glenohumeral ligament [19]
  • A large capsular recess and disruptions of the glenolabral socket [20, 18, 21, 22, 23, 24]
Computed tomography (CT) arthrogram of a shoulder Computed tomography (CT) arthrogram of a shoulder with atraumatic posterior instability demonstrates a patulous posterior capsule consistent with excessive capsular laxity.

Many authors have emphasized that posterior stability is heavily dependent on the integrity of the inferior glenohumeral ligament.[25, 26, 27, 28]

Alteration of the stabilizing forces of the glenohumeral joint has been implicated in contributing to the pathophysiology of posterior instability. Posterior instability usually occurs in midrange shoulder motion when the stabilizing ligaments of the humeral head are not under tension. Therefore, disruption of the capsuloligamentous structures cannot be solely responsible for instability. Three mechanisms that have been identified as the primary stabilizing forces of the glenohumeral articulation during the midrange motion are as follows[29, 30, 31] :

  • Geometric conformity of the articular surfaces
  • Labral contribution to the glenoid fossa depth, thereby increasing resistance to translation of the humeral head
  • Muscular force compressing the humeral head into the glenoid fossa

An alteration of one or more of these stabilizing forces, therefore, contributes to posterior instability.

The contribution of the rotator interval also has been recognized as an important static restraint in preventing posterior and inferior instability. In their cadaveric study, Harryman et al reported that imbrication of the rotator interval assists in preventing posterior and inferior instability.[32] Selective cutting studies of the glenohumeral joint also have determined the importance of the anterior ligamentous structures on posterior instability.[33]

Labral injury has been described in association with posterior instability (see the image below). Pathologic lesions have been identified, such as the following[34, 35] :

  • Posterior labral tear
  • Posterior capsular stripping or laxity
  • Fracture, erosion, sclerosis and ectopic ossification of the posterior glenoid fossa
  • Reverse Hill-Sachs lesions

Labral lesions have also been described in the impact athlete in whom the posterior glenohumeral compressive force is increased.[36] This causes a greater resultant shear force imparted to the posterior labrum and articular surfaces with forced translation.

Arthroscopic examination of a patient with recurre Arthroscopic examination of a patient with recurrent posterior instability reveals significant fraying and tearing of the posterior labrum.

An isolated pathologic lesion responsible for posterior instability is rare. Posterior instability is typically multifactorial in nature, and accurately identifying all the causative agents preoperatively is difficult. The operating surgeon must be aware of all potential pathophysiologic clues so that when identified during the operative procedure, these causes can be corrected.

Definition and classification

An absolute definition of shoulder instability is difficult to formulate and has been the center of a vast amount of research. Whereas isolated traumatic dislocations can be described by their relationship to the bony landmarks of the shoulder, instability without formal dislocation may be much more difficult to ascertain. One must differentiate between shoulder laxity, which is a physiologic variant of normal, and shoulder instability, which is a symptomatic, pathologic process.

Posterior glenohumeral dislocations typically lie behind the glenoid and beneath the acromion (subacromial). In rare instances, the humeral head may be positioned behind and under the glenoid (subglenoid) or medial to the acromion and beneath the scapular spine (subspinous).[37]

Hawkins and McCormack described three categories of posterior glenohumeral instability, as follows[38] :

  • The first category included acute posterior dislocations and was subdivided into those with and those without impression defects of the humeral head
  • The second category comprised chronic posterior dislocations (locked or missed with an impression defect)
  • The third category included recurrent posterior subluxation and was divided into voluntary and involuntary groups

In the third category, the voluntary group was subdivided into the habitual (willful) subluxation secondary to personality disorder and subluxation caused by voluntary muscle control. The involuntary group was subdivided into positional (not willful but demonstrated by the patient) and nonpositional (not demonstrable by the patient).

Other classification systems also have been described for posterior glenohumeral instability. Dimon classified posterior dislocations according to the mechanism of injury, as follows[39] :

  • Traumatic
  • Postconvulsive
  • Voluntary posterior subluxation-relocation
  • Recurrent posterior dislocation (requiring repeated reduction)
  • Without history of trauma or convulsion

Instability or subluxation of the glenohumeral joint has been simply classified according to whether it results from a traumatic or a nontraumatic injury. It can be subdivided into voluntary and involuntary cases.[37] The direction of instability also has been used to classify the pathology.[40] The direction of instability can be unidirectional (posterior only), bidirectional (posterior and inferior), or multidirectional (posterior, inferior, and anterior) and is important to determine in planning the surgical approach.

Posterior shoulder instability is also a well-recognized consequence of neonatal brachial plexus injury, such as Erb palsy. Such dislocations have been reported in children as young as 6 months.[41]

Waters et al, from Boston Children's Hospital, used computed tomography (CT) or magnetic resonance imaging (MRI) to prospectively study 42 patients with birth palsy.[42] They found a 62% rate of posterior shoulder subluxation. Persistent internal rotation contracture is thought to be the primary culprit responsible for significant glenoid dysplasia (and resultant posterior instability) that is typically quite advanced by age 2 years.[43]

Etiology

Posterior instability is thought to be secondary to three types of etiologic processes, as follows[20, 44, 45] :

  • Major injury
  • Repetitive minor trauma
  • Virtually atraumatic process

Major injury of the glenohumeral joint can occur directly or indirectly to the shoulder.

Direct trauma to the anterior shoulder or axial loading of a flexed, adducted, internally rotated arm may cause a posterior dislocation. Indirectly, posterior dislocations can occur secondary to violent muscle contractions associated with seizures or electrical shock. In this condition, the strong internal rotation forces of the latissimus dorsi, the pectoralis major, and the subscapularis overpower the relatively weaker external rotator muscles.[25]

Pure, isolated, unidirectional posterior subluxation of the glenohumeral joint is rare.[40, 16] Most cases have either an inferior component (bidirectional) or inferior and anterior components (multidirectional), secondary to generalized ligamentous laxity or to repetitive microtrauma causing either stretching of the static restraints or weakness of the dynamic restraints.

Epidemiology

Recurrent posterior instability of the glenohumeral joint is less common than anterior instability, representing fewer than 5% of shoulder dislocations in most series.[20] Early in the published experience, McLaughlin reported 22 posterior dislocations or subluxations in 581 shoulder dislocations, an incidence of 4%.[3] In subsequent publications, the incidence was reported to be 2-12% of all cases of shoulder instability.[46]

Lanzi et al studied 1348 shoulder injuries at the United States Military Academy from 2006 to 2012 and reported that intercollegiate athletes and weightlifters were likelier to require surgical treatment than intramural athletes.[47] Frank et al found it prevalent among football and rugby athletes.[48]

 

Prognosis

Historically, surgical repairs for posterior instability have had mixed results, with failure rates as high as 50% reported in the literature. Overall, surgical intervention is associated with a 50-95% success rate.[49, 50, 51, 52]

Because of differences regarding classification and terminology, most studies have combined groups of patients with trauma, multidirectional laxity, unidirectional or multidirectional instability, voluntary subluxation, and intentional or positional instability. Consequently, the results of treatment are often not reported for one well-defined variant of the condition.

The rates of recurrence after a posteroinferior capsular shift procedure for posterior instability are higher than the rates of repair for anterior instability. Nonetheless, most shoulders improve from the procedure, and the patients are satisfied. The rate of recurrence after a posteroinferior capsular shift performed as a posterior revision operation is prohibitive when the infraspinatus or the deltoid has been damaged.[22, 53] The best procedure for posterior instability, however, is currently unknown; the technique, therefore, must be individualized to the specific needs of the patient.

Within the context of a 2- to 5-year follow-up, reduction of posterior shoulder dislocation in younger children appears to be associated with improved shoulder motion and function. Hoffer recommended that in such situations, reduction of the shoulder joint should be accompanied by release of the pectoralis major and transfer of the latissimus dorsi and the teres major.[54, 55] In older children (Hoffer suggested age 7 years as a possible threshold), rotational osteotomy is an option.

Kirkos and Papadopoulos reported on 22 of their rotational osteotomy patients (age range, 4-17 years), four of whom demonstrated posterior shoulder subluxation. Improved function in activities of daily living was documented, as were average increases in abduction and rotation of about 25°.[56]

The images below illustrate the anteroposterior (AP), scapular-Y, and axillary radiographs of the right shoulder of a 7-year-old girl with severe upper brachial plexus palsy. Note the marked glenohumeral dysplasia and frank posterior shoulder dislocation. The child's severe loss of shoulder motion prevented her from performing many activities, including combing her own hair.

Anteroposterior radiograph of 7-year-old girl with Anteroposterior radiograph of 7-year-old girl with brachial plexus palsy.
Scapular-Y view. Scapular-Y view.
Axillary view. Axillary view.

After rotational osteotomy her function (including the ability to comb her hair) was significantly improved (see the images below).

Postoperative anteroposterior radiograph showing h Postoperative anteroposterior radiograph showing healed osteotomy site.
Postoperative lateral radiograph. Postoperative lateral radiograph.

In a systematic review and meta-analysis of the available literature on clinical outcomes for posterior shoulder instability, DeLong et al reached the following conclusions[57] :

  • Arthroscopic procedures are effective and reliable for treating unidirectional posterior glenohumeral instability with regard to outcome scores, patient satisfaction, and return to play
  • Compared with contact athletes or the overall population of athletes, throwing athletes have a lesser chance of returning to their preinjury levels of sport
  • In young adults who take part in highly demanding physical activity, the rates of recurrence and revision are lower with arthroscopic stabilization procedures using suture anchors than with anchorless repairs
  • Arthroscopic treatment results in better outcomes than open surgical treatment with regard to stability, recurrence of instability, patient satisfaction, return to sport, and return to previous level of play

Following a review of 93 studies, Bäcker et al found that the best outcomes were reported when arthroscopic capsulolabral repair was combined with postoperative rehabilitative care.[58]

 

Presentation

History

A thorough history is invaluable during the clinical assessment of posterior glenohumeral instability. One must determine the type and mechanism of the event that originally caused the instability (major trauma, repetitive minor trauma, or an atraumatic process).

A history of violent trauma, seizures of any etiology, or electrical shock should alert the physician to search for a posterior dislocation. Patients without a history of major trauma typically report painful symptoms initially that diminish over time. These patients commonly report difficulty in performing activities of daily living, including hair combing, shaving, and eating.[38]

Athletic activities that require the arm to be placed in flexion, adduction, and internal rotation commonly cause symptoms of pain and the sense of instability. Common activities include throwing (follow-through), bench press (lockout), swimming (pull-through), and rowing.[20]

Pain is usually limited to the instability episodes, though many patients report posterior joint line pain or vague anterior pain, which may be thought of as one of Neer's causes of nonoutlet impingement.[16] Finally, it is important to determine whether the patient has a voluntary type of instability or a positional type of involuntary instability.

Physical Examination

Physical examination of a posterior glenohumeral dislocation may reveal prominence of the humeral head posteriorly, with flattening of the anterior contour and prominence of the coracoid. These findings can often be quite subtle and often are obliterated by swelling or a large deltoid muscle mass.[39]

External rotation of the arm is significantly limited, while flexion and internal rotation can be remarkably normal. Rowe and Zarins described examination of the shoulder with flexion of both elbows to 90° to demonstrate a fixed humeral internal rotation deformity.[59] Comparison of the external rotation available on both sides reveals the internal rotation deformity on the dislocated side. With the arm extended, the patient's palm also does not turn fully upward on the affected side, despite full forearm supination due to the fixed internal rotation.

Examination maneuvers for posterior instability are not often dramatic. Palpatory examination may reveal tenderness of the posterior joint line and tenderness of the anterior dynamic stabilizers. Range of motion (ROM) is typically normal, though patients sometimes have a loss of external rotation with the arm abducted at 90°.[25] Testing for generalized ligamentous laxity should be performed. Specific tests for posterior instability include the posterior drawer test (see the image below).

Intraoperative examination under anesthesia of a p Intraoperative examination under anesthesia of a patient with atraumatic posterior instability demonstrates, via a posterior drawer test, significant posterior subluxation of the glenohumeral joint.

The posterior apprehension test (ie, the jerk test) also can be used for this purpose. The examination involves applying an axial posterior load onto an arm flexed at 90°, adducted, and internally rotated; it is positive with reproduction of the instability sensation (see the video below). Hawkins and McCormack suggested flexing the arm to recreate the position in which subluxation occurs and stated that a "clunk" occurs as the arm is elevated to 120°.[38]

Physical examination of this patient with atraumatic posterior instability demonstrates significant posterior glenohumeral translation with the jerk test.

A posterior drawer/relocation test, in which pain or apprehension occurs with a posterior directed force and is relieved by reduction, may be the preferred diagnostic maneuver.[60] The extent of translation during diagnostic examination has been graded as follows[49, 50, 51] :

  • +0 - No translation from being centered in the glenoid fossa
  • +1 - Translation noticeable but not up to the glenolabral rim (without a clunk)
  • +2 - Translation of humeral head onto the glenolabral rim (clunking without locking)
  • +3 - Translocation over the glenolabral rim (locking in the subluxated position that reduces without manual reduction)
  • +4 - Translation with complete dislocation (locking in the dislocated position that requires manual reduction)

Examination in the office and under anesthesia involves a thorough evaluation for motion, laxity, and stability. Patients without symptoms may have as much translation as those requiring surgical repair for symptomatic shoulder instability. The need for surgical reconstruction should, therefore, be based on the history and physical examination findings rather than on the magnitude of translation alone.

Finally, evaluation of other potential components of instability—including through the sulcus test (as described by Neer and Foster[17] ), for inferior instability, and through the crank test, for anterior instability—is equally important.[49, 50, 51]

 

Workup

Imaging Studies

Radiography

Posterior dislocation

Radiographic views for posterior dislocation include anteroposterior (AP) internal and external rotation views, an axillary lateral view, and a scapular-Y view. Posterior dislocations are often missed on standard AP radiographs alone (see the image below).

Anteroposterior radiograph of this shoulder demons Anteroposterior radiograph of this shoulder demonstrates an impression defect in the humeral head; however, the posterior dislocation is not readily apparent on this view.

Because the humeral head is fixed in internal rotation, the standard internal and external rotation views yield the same image, and obliteration of the greater tuberosity creates a light-bulb appearance of the humeral head. The acromiohumeral distance is decreased compared with that of the normal side, and the normal overlap of the humeral head on the glenoid is lost.

The best radiographic view for diagnosing a posterior dislocation is the axillary view, which allows identification of the glenohumeral relationship. Locked posterior dislocations are readily apparent on the axillary view. Evaluation using this view is also made for posterior translation, reverse Hill-Sachs lesions, and posterior glenoid rim pathology.

The scapular-Y view can be helpful; however, interpretation can occasionally be difficult because of variations of the beam angle.

Posterior instability

Radiographic views for posterior instability include AP views in internal and external rotation, a Stryker notch view, and a West Point or axillary view. Findings on radiographs for instability are often normal; however, occasional osseous pathology can be found.

A reverse Hill-Sachs lesion can be seen on the external rotation view.

The axillary view is used to note such lesions as glenoid hypoplasia, excessive glenoid retroversion, erosion or fracture of the posterior glenoid rim, lesser tuberosity fractures, and extra-articular ossific lesions of the posterior glenoid (Bennett lesion). Bennett lesions are seen primarily in high-level throwers but do not necessarily represent shoulder instability.[61] Schwartz et al found that 20% of patients had capsular calcification along the posterior aspect of the capsule and labrum and that 20% had 2-4 mm of bony erosion of the posterior glenoid rim on an axillary view.[25]

Computed tomography

Computed tomography (CT) also can be used to evaluate osseous involvement, such as glenoid retroversion or hypoplasia and a reverse Hill-Sachs lesion or glenoid rim damage.[62] (See the image below.) Glenohumeral instability is associated with a low percentage of shoulders with bony abnormalities. CT arthrography may assist with visualization of labral pathology or excessive posterior capsular redundancy when present.[63]

Axial cuts of the postreduction computed tomograph Axial cuts of the postreduction computed tomography (CT) scan demonstrate the anterior impression defect with persistent posterior subluxation of the humeral head.

Magnetic resonance imaging

Magnetic resonance imaging (MRI) helps rule out rotator cuff pathology but has been an inconsistent tool for identifying labral and capsular involvement in posterior instability. MRI arthrography may assist with the evaluation of labral pathology if present.

The efficacy of MRI in identifying posteroinferior labral abnormalities has been questioned, perhaps because of capsular redundancy in this region. In postoperative cases especially, the usefulness of MRI is limited, and this study usually is not obtained.[61, 64]

MRI can be valuable in the assessment of capsular stripping, bony infractions, and subscapularis avulsion. It can also aid in the accurate diagnosis of glenoid retroversion, glenoid dysplasia, and increased posterior capsular area.[65, 66]

Other Tests

Electromyography (EMG) and nerve conduction studies can be helpful in clarifying unexplained weakness and in documenting the presence of neurologic injury, particularly in patients in whom revision surgery is planned. The axillary and suprascapular nerves can be injured in the posterior approach to the shoulder.

Documentation of preexisting neurologic lesions is important before further reconstructive attempts are made, especially in cases involving litigation.

 

Treatment

Approach Considerations

The primary indication for surgery for posterior glenohumeral instability is recurrent symptomatic shoulder subluxation or dislocation that is recalcitrant to conservative measures. Surgical treatment should be considered only in patients who remain significantly disabled after an adequate trial involving strengthening exercise and avoidance of provocative positions.

Burkhead and Rockwood stressed that 80% of patients with an atraumatic cause of shoulder instability, in contrast to 16% of those with traumatic instability, improve with an exercise program alone.[67] Others reported that 70% of athletes subjectively improve with a conservative program.[45, 15] The instability, however, is usually not eliminated, but the functional disability during athletics is improved, allowing the patient to participate in his or her sport without problems.

All patients who subluxate voluntarily should undergo the appropriate psychological evaluation before operative treatment is recommended. Patients with positional instability in which the humeral head subluxes posteriorly when the arm is adducted at 90° of flexion have a good response to surgical intervention.[22, 24, 68] Surgical intervention is associated with a 50-95% success rate.[49, 50, 51]

Children with posterior shoulder instability secondary to neonatal brachial plexus injury fall into two general categories: early and late. In children in whom the diagnosis is established early (usually before age 2 years), reconstructive and tendon-balancing procedures are options.[54, 55] In many children who present late with established dislocations, rotational osteotomy of the proximal humerus (with or without additional soft-tissue procedures) can significantly improve shoulder function.[56, 69]

Specific contraindications for surgical treatment of posterior shoulder instability include situations in which conservative treatment, including activity modification and a formal exercise program, has not been attempted. The length of a trial of conservative treatment before surgery varies, but Tibone and Bradley recommended continuing an exercise protocol for at least 6 months before resorting to surgical treatment.[45]

Many patients become asymptomatic in terms of pain and function after completing a physical therapy protocol, though clinically, the instability may persist.[15] McIntyre et al concluded that rotator cuff and posterior deltoid strengthening may help patients manage symptoms and improve function.[70]

Patients with voluntary instability of the shoulder who have a psychological disorder or who are seeking secondary gain are not candidates for surgical reconstruction. Any patient in whom voluntary instability is suspected should be evaluated by a mental health specialist to screen for underlying psychological conditions.

Medical Therapy

Nonoperative treatment for acute posterior shoulder dislocations involves an attempt at closed reduction. After muscle relaxation is achieved, traction is established in an adducted position, in line with the deformity, with the patient supine. The humeral head is gently lifted into the glenoid fossa. Forced external rotation is avoided because a head locked on the glenoid rim may lead to fracture of the humeral head or shaft. Lateral traction may be combined with longitudinal traction with a soft towel or sheet.

The shoulder is immobilized for 6 weeks in 20° of external rotation; an exercise program follows, designed to achieve painless range of motion (ROM), a normal scapulohumeral rhythm, and strengthening of the dynamic restraints.

Fixed posterior dislocations are rarely treated nonoperatively. Nonoperative treatment is reserved for patients who are inactive or poor surgical risks. In this situation, a reasonable goal is to provide the patient with a painless compensatory ROM to perform the activities of daily living.

All patients with posterior shoulder subluxation should undergo a trial of nonoperative care before surgery is considered. An exercise program that develops a pain-free ROM, a normal scapulohumeral rhythm, and strengthening of the dynamic restraints is recommended.

Burkhead and Rockwood evaluated the efficacy of specific muscle strengthening exercises to treat anterior, posterior, and multidirectional instability.[67] The two-phase exercise program, which the patients performed at home, provided progressive resistance training of the rotator cuff muscles and deltoid. Only 15% of patients with a traumatic etiology for their instability had good or excellent results. This was compared with 83% good or excellent results in patients with an atraumatic etiology for their instability.

Engle and Canner suggested a more comprehensive three-phase program relying on manual proprioceptive neuromuscular facilitation (PNF) and multiple changes of training types (from progressive resistance exercises to isokinetics, isometrics, concentric loading, and eccentric loading).[71] The rigorousness of this program mandates constant monitoring by a physical therapist.

An exercise program typically is continued for at least 6 months in an attempt to strengthen the shoulder musculature and decrease any functional disability.[2] Seventy percent of athletes in Tibone and Bradley's study subjectively improved with a conservative program.[45]

The instability, however, is usually not eliminated by an exercise program, but the functional disability during athletics is improved, allowing the patient to participate in his or her sport without problems. Athletes who respond to conservative care are usually satisfied, can tolerate their instability, and need no further treatment.

Surgical Therapy for Posterior Dislocations

Surgery for a posterior shoulder dislocation can be difficult, particularly for a joint that has not been reduced for some time or has extensive damage to the humeral head or glenoid. Hawkins et al established guidelines for the management of posterior dislocations on the basis of how long the shoulder has been dislocated and what percentage of the humeral head has been involved with the articular surface defect (reverse Hill-Sachs defect).[72]

Closed reduction is recommended if the dislocation was within the previous 6 weeks and if, on axillary radiography, the articular defect involves less than 20% of the articular surface.[72] If the arm is stable, it is immobilized in 20° of external rotation for 6 weeks. If it is unstable, the Neer modification of the McLaughlin procedure (see below) is recommended, followed by immobilization.

For dislocations present for 6 weeks to 6 months and involving 20-45% of the articular surface, either a McLaughlin procedure or the Neer modification is recommended, again followed by immobilization in external rotation. With a normal glenoid and greater than 45% humeral head involvement in a dislocation that occurred more than 6 months earlier, hemiarthroplasty is recommended.

Surgical Therapy for Locked Posterior Dislocations

Subscapularis transfer (McLaughlin procedure)

In 1952, McLaughlin described the technique of subscapularis transfer from the lesser tuberosity into the anterior articular defect (Hill-Sachs defect) for locked posterior dislocation or recurrent posterior instability.[3] McLaughlin reported good to excellent results in three of three locked posterior dislocations and two of two recurrent subluxations.

Hawkins et al reported good-to-excellent results in four patients treated with this technique who had articular defects of 20-45% of the humeral head; five patients referred to them with failures of this procedure had articular defects of greater than 45%.[72]

Lesser tuberosity transfer (Neer modification of McLaughlin procedure)

Working from the theory that bone heals to bone better than to tendon, Neer modified McLaughlin's technique by transferring the subscapularis tendon with its lesser tuberosity insertion into the humeral head defect and securing it with screws. Four of four patients in Neer's study had good or excellent results.

Allograft reconstruction of humeral head defect

Gerber described a technique of allograft reconstruction of segmental defects of the humeral head for chronic locked posterior dislocations.[73] An allograft femoral head with articular surface was contoured to the shape of the humeral head defect and secured with screws. Four patients with defects of at least 40% were treated with this technique. Three of the four reported little or no pain; one, after being symptom-free for 6 years, experienced severe dysfunction secondary to avascular necrosis (AVN) of the remaining portion of the humeral head.

Arthroplasty

With a normal glenoid and greater than 45% humeral head involvement, hemiarthroplasty is recommended for a dislocation that has been present for more than 6 months. Total shoulder arthroplasty is recommended when the glenoid is significantly involved (see the image below). A bone graft from the involved humeral head can be used for glenoid bone loss. The normal humeral head retroversion of 30-40° may predispose a prosthesis to further instability. Therefore, a compensatory relative anteversion should be used during insertion of the humeral component.

Because this elderly patient also had glenoid arth Because this elderly patient also had glenoid arthritis, ultimate treatment was total shoulder arthroplasty.

Hawkins recommended neutral version for a shoulder that has been dislocated for longer than 6 months and approximately 20° of retroversion for a dislocation that has occurred within the previous 6 months.[72]

Pritchett reported that of seven patients treated with arthroplasty for anterior or posterior chronic dislocation, all improved over their preoperative status, with five good results and two fair results.[74]

Cheng reported that total shoulder arthroplasty for locked posterior dislocations reliably decreased the patient's level of pain, improved range of motion, and significantly improved level of function. Use of a secondary posterior incision facilitating the extrication of the humeral head also was described.[75]

Surgical Therapy for Chronic Posterior Instability

Because of the infrequent nature of recurrent posterior subluxation and the variable results of surgical intervention, many small series have been reported, each employing a different treatment technique. In patients refractory to conservative measures, surgical treatment may be considered. Surgical treatment for posterior instability has historically included the following procedures:

  • Subscapularis transfer
  • Biceps tendon transfer with staple capsulorrhaphy
  • Reverse Bankart repair
  • Reverse Putti-Platt repair
  • Infraspinatus advancement
  • Posterior/inferior capsular shift
  • Glenoid osteotomy
  • Humeral osteotomy
  • Posterior bone block
  • Posterior staple capsulorrhaphy
  • Various combinations of the above

Reverse Bankart procedure

Rowe and Yee described the reverse Bankart procedure in two patients, using drill holes placed through the glenoid rim to the medial bone and then securing the capsular flap with mattress sutures.[12] In both of the cases described, the patient regained normal function.

Reverse Putti-Platt repair

The reverse Putti-Platt procedure was originally described by Severin,[76] who shortened the infraspinatus only, and DePalma,[77] who shortened the infraspinatus and the teres minor together. A subsequent report on this procedure stated that 16 out of 17 patients had excellent results and no recurrent subluxation or dislocation.

Biceps tendon transfer with staple capsulorrhaphy

Boyd and Sisk described the use of a biceps tendon transfer in conjunction with posterior capsulorrhaphy for recurrent dislocations of traumatic origin or voluntary subluxations that become involuntary.[23] In the biceps tendon transfer, the long head of the biceps was placed posteriorly, secured to the glenoid rim with the capsule by a staple.

Opening wedge osteotomy

In 1967, Scott first described the use of an opening wedge osteotomy to correct excessive glenoid retroversion.[78] A broad osteotome was used to perform the medially directed osteotomy from the supraglenoid tubercle to the origin of the long head of the triceps. The glenoid neck was then wedged open with a portion of the removed acromion. Brewer et al reported good or excellent results in five of five patients and recommended iliac crest bone graft instead of bone graft with an osteotomized piece of acromion.[14]

Complications following this technique include recurrence of instability, osteoarthritis, AVN secondary to joint penetration, and coracoid impingement. Bone block procedures to the posterior glenoid have been shown to act as a buttress against posterior subluxation.[79, 80]

Autologous iliac crest graft

The use of an autologous iliac crest graft from the posterior superior iliac spine was first described in 1949 by Fried, who reported recurrence of instability, attributed to resorption of the bone graft, in one of five patients.[81] Some authors have advocated the use of a posterior bone block in combination with another procedure.

A variation of the open wedge glenoid osteotomy—using a vascularized bone graft taken from the scapular spine with its adjacent posterior deltoid pedicle—was described by Cziffer et al.[82] The authors used this procedure for revision instability repair when posterior glenoid deficiency or retroversion greater than 30° was present.

Rotational osteotomy of humerus

Variations in the version of both the humerus and glenoid have been theorized as disposing factors in glenohumeral instability. Chaudhuri described a rotational osteotomy of the humerus whereby the humeral shaft is externally rotated in recurrent posterior dislocations.[83] Reported complications following this procedure have included recurrence of instability and pseudoarthrosis of the humeral osteotomy site.

Surin reported good or excellent results in 10 of 12 patients with posterior instability.[84] Rotational osteotomy of the humerus has also been described for locked posterior dislocations of the shoulder.[85]

Chronic posterior instability lesions

Typical lesions in chronic posterior instability include posterior labral fraying and tears, a patulous capsule, and, rarely, osteoarthritis of the glenohumeral joint. (See the image below.)

Arthroscopic examination demonstrates significant Arthroscopic examination demonstrates significant capsular laxity with a large, redundant posterior recess.

Interestingly, reverse Bankart lesions are extremely rare in patients who have true posterior subluxation without a prior history of a significant isolated traumatic episode causing a posterior dislocation.[2] Because posterior instability appears to be a capsular problem, procedures have been designed that specifically address this problem (see the images below).

The posterior approach to the shoulder begins at t The posterior approach to the shoulder begins at the posterolateral border of the acromion and extends to the axilla.
The capsule is exposed by splitting the deltoid in The capsule is exposed by splitting the deltoid in line with its fibers, followed by dissection of the infraspinatus/teres minor interval. A horizontal incision is then made in the capsule to expose the joint.
A Fukuda retractor is inserted to retract the hume A Fukuda retractor is inserted to retract the humeral head and expose the posterior glenoid rim.
Suture anchors are inserted into the glenoid rim. Suture anchors are inserted into the glenoid rim.
The sutures are used to perform the capsulorrhaphy The sutures are used to perform the capsulorrhaphy and are then tied.
Completion of the procedure demonstrates significa Completion of the procedure demonstrates significant reduction of the posterior capsular redundancy.

Posterior capsulorrhaphy

Posterior capsulorrhaphy with suture fixation is currently the open procedure of choice. In the past, this treatment was performed with staple fixation; however, staples have been found to cause metal complications about the shoulder and are no longer recommended. Posterior capsular shift procedures have been described by several surgeons, including Neer, Rockwood, and Warren.

Neer technique

Neer's technique begins with a vertical skin incision and blunt dissection through the deltoid. The infraspinatus tendon is divided obliquely so that the superficial portion can be attached to the scapula to reinforce the posterior portion of the capsule. A horizontal capsular incision is made lateral to the tuberosity, with further extension for additional inferior laxity.

A T-shaped opening is made in the posterior capsule at the humeral side to form a superior flap and an inferior flap. The inferior flap is completed by detachment of the capsule from the neck of the humerus to its inferior aspect. During this step, the arm is kept internally rotated. The axillary nerve is carefully protected by using a Darrach retractor and by leaving the teres minor intact.

The arm is positioned in 20-40° of external rotation. The humeral neck is decorticated with a curette or burr. The superior flap is pulled downward and reattached. The inferior flap is then pulled backward and upward over the secured superior flap, thus reducing the redundancy of the capsule anteriorly, inferiorly, and posteriorly. If significant inferior instability exists, the inferior flap is advanced first in a pants-over-vest fashion.

The capsular flaps are reinforced with the superficial part of the infraspinatus tendon and brought down and sutured against raw bone on the scapular neck. The deep portion of the infraspinatus tendon is sutured over this so that it will remain a strong external rotator.

Bigliani et al reported good or excellent results in 28 of 35 shoulders treated with this technique.[21] Four shoulders became unstable; in six of the seven shoulders in which unsatisfactory results were recorded, previous stabilization attempts had been made.

Fuchs et al reported on 26 shoulders treated with this technique and found that it produced very satisfactory intermediate-term clinical results.[53] Recurrence was associated with a previous operation on the posterior aspect of the shoulder or with a new traumatic injury of an involved shoulder on the dominant side. The prevalence of recurrence did not increase over time, and clinically detectable osteoarthritis did not develop.

Rockwood technique

Rockwood's technique also begins with a vertical skin incision, blunt dissection through the deltoid, and a vertical incision through the infraspinatus tendon, which is reflected medially. If the muscle is particularly lax, the interval between the infraspinatus and the teres minor is split. A vertical capsular incision is made midway between the humerus and glenoid and extended inferiorly to address laxity. This creates a medial- and lateral-based flap.

The arm is placed in neutral rotation. In a pants-over-vest fashion, the medial flap is advanced superiorly and laterally under the lateral flap. The overlying lateral flap is advanced superiorly and medially over the medial repair.

Other techniques

Fronek et al described a technique of posterior capsulorrhaphy with or without a bone block for posterior subluxation.[24] A horizontal or vertical skin incision is made, and the infraspinatus is divided with a vertical incision and reflected medially. A vertical capsular incision is made near the glenoid margin with a T-horizontal incision from the middle of the glenoid to the humerus. Alternatively, to address excessive inferior laxity, an additional horizontal incision is made at the humeral border of the capsule, creating an H-shaped incision.

The inferior flap is advanced medially and superiorly and repaired to the medial glenoid to address inferior laxity. The superior flap is then pulled downward and used to reinforce the inferior flap. If a loose labrum is present, drill holes are placed into the underlying bone. The labrum is sutured to the bone and the capsule advanced. If needed, a bone graft can be used as well.

In the study by Fronek et al, 11 patients were treated operatively, with a 91% success rate.[24] Sixteen patients in the study were treated conservatively with physical therapy, with a success rate of 63%.

Knowledge has been expanding regarding the significant role of the coracohumeral and superior glenohumeral ligaments in posterior instability. Several authors have adopted an anterior surgical approach to correct posterior instability. Nobuhara and Ikeda performed rotator interval reconstructions in patients with posteroinferior instability.[86] Of the 78 patients evaluated, they reported 96% good or excellent results, with recurrent instability reported in 4% of cases (three patients).

Brems reported excellent results in 86% of patients after a posterior inferior capsular shift that was performed through an anterior approach; this technique was used to treat posterior instability in shoulders that had not previously undergone surgery.[87] However, Brems reported poor results in 86% of patients after performing the same technique on shoulders that had undergone previous posterior reconstructive procedures.

Wirth et al described a capsulorrhaphy through an anterior approach for the treatment of a traumatic posterior glenohumeral instability with multidirectional laxity of the shoulder.[88] The procedure involved closure of the capsule in the rotator interval and imbrication of the capsule's anterior, inferior, and posteroinferior aspects with a double-breasting technique that decreased the overall capsular volume. Of the 10 patients treated, nine had good or excellent results.

Subsequent advances in arthroscopic technique have led to the development of procedures to address posterior glenohumeral instability. The use of a biodegradable Suretac device has been described. McIntye et al reported the 2-year results on a multiple-suture technique for posterior instability.[89] Their technique involved a capsular repair of the posterior band by sutures tied into the inferior capsule and then brought up to the superior portal and tied over the fascia of the trapezius or bone. They reported 17 good or excellent results and four fair or poor results. Two recurrent dislocations and three subluxations occurred, for an overall recurrence rate of 25%.

Wolf reported on 14 patients (minimum follow-up, 2 years) who underwent posterior capsular plication with or without suture anchors.[46] Twelve patients had excellent results, and two had fair results.

Antoniou reported a large study of 41 patients who were treated with an arthroscopic capsular shift of the posteroinferior aspect of the capsule to the adjacent labrum and were monitored for a minimum of 12 months.[49] The mean score on the simple shoulder test improved statistically, as did two of the eight Short-Form 36 (SF-36) parameters. Thirty-five patients had improved stability, and 28 had a perception of residual stiffness.

Bradley et al reported a prospective review of 100 shoulders in 91 athletic patients.[90] The patients were treated for unidirectional posterior glenohumeral instability with an arthroscopic capsulolabral plication, either alone or, in the event of a concomitant labral tear, with suture anchors. The researchers demonstrated an effective arthroscopic procedure with regard to stability, pain relief, and functional restoration in an athletic population.

In this study,[90] subjective stability and pain scale scores improved significantly compared with preoperative values. Functional American Shoulder and Elbow Surgeons (ASES) scores improved significantly, with postoperative ROM mean subjective scores within the satisfactory to full ROM. Standardized ASES shoulder scale scores improved significantly with this procedure, with an overall 91% excellent or good result. Patients were able to return to the same competitive level in their respective sport 67% of the time, with 22% reporting a return to their sport at a limited level; 11% did not return to competition, because of their shoulder injury.

In another study of 200 shoulders in 183 athletes, Bradley et al reported greater improvement in patients when bone suture anchors were incorporated into capsulolabral reconstruction.[91]

Detachment of the posterior glenoid labrum and capsule below the equator of the glenoid (ie, a posterior Bankart lesion) can be particularly debilitating for patients and challenging for caregivers to effectively manage.

In a retrospective review by Williams et al, traumatic posterior Bankart lesions in 27 shoulders were arthroscopically treated with capsulolabral repair.[92] At follow-up (mean, 5 years), no patient exhibited deficits in range of motion or any instability of humeral head translation beyond the glenoid rim (+1). Pain and instability were eliminated in 92% of patients. Two patients required further surgical intervention: One ultimately required an open capsulorrhaphy, the other a repeat arthroscopy for labral debridement.

Similarly, Kim et al presented an evaluation of their results of arthroscopic treatment of 27 patients with traumatic unidirectional recurrent posterior subluxation of the shoulder, at a mean follow-up of 39 months.[93] All patients were treated with nonabsorbable sutures and/or suture anchors, with repair of labral lesions and a superior shift of the posterior capsule. All patients had improved shoulder function scores, and all but one patient had stable shoulders according to subjective and objective measurements.

One study retrospectively reviewed 31 shoulders treated for traumatic posterior shoulder instability; the report compared findings from open posterior stabilization (12 cases) and arthroscopic stabilization (19 cases) for various shoulder outcome instruments.[94] Follow-up averaged 40 months, and 29 of 31 shoulders rated as excellent or good following surgical intervention. Significant differences were noted between the arthroscopic and open methods of fixation for instrument measurements for disability (Western Ontario Shoulder Instability Index [WOSI]) and function, stability, and ROM (Rowe), with arthroscopic repair showing the more favorable results.

Results from other methods of evaluation, comparing subjective results (Single Assessment Numeric Evaluation [SANE]) and function with return to sport (Simple Shoulder Test [SST]), were not significantly different for the open and arthroscopic methods.[94] However,the results of these instruments did favor the arthroscopic methods of fixation.

In a study of 56 American football players with unidirectional posterior shoulder instability, Arner et al found that arthroscopic posterior capsulolabral repair, with or without suture anchors, yielded excellent or good results in 96.5% of patients.[95] Stability, pain, and joint function were all improved, thus increasing the likelihood of successful return to play.

Postoperative Care

Immobilization of the shoulder with some variation is recommended for approximately 6 weeks. Historically, the method of immobilization has involved use of a spica-type cast. Newer, prefabricated braces have been developed, including the gunslinger brace (see  the image below) and the DonJoy UltraSling.

Postoperative immobilization in a gunslinger brace Postoperative immobilization in a gunslinger brace demonstrates appropriate positioning in external rotation.

The key to postoperative bracing is the position in which the shoulder is held. As recommended in the literature, the degree of external rotation should be between neutral and 45°, and abduction should be between neutral and 90°. The common goal is to allow healing through relaxation of the posterior structures.

Complications

Complications associated with posterior glenohumeral instability surgery can be divided into early and late problems. Early problems include the following:

  • Incorrect diagnosis
  • Glenoid fracture
  • Humerus fracture
  • Neurovascular injury
  • Infection
  • Recurrence of instability

Late complications include the following:

  • Incorrect diagnosis
  • Recurrence of instability
  • Pain
  • Stiffness
  • Hardware protrusion into the joint
  • Osteoarthritis
  • Infection

The most common complication following posterior stabilization surgery is recurrence of instability, with rates averaging 15-20%.[20, 61] Open and arthroscopic techniques used to treat posterior instability have both been associated with a high recurrence rate in comparison with similar open or arthroscopic treatment of anterior instability.

The athlete may have a successful surgical outcome with the elimination of posterior instability, but as many as 50% of patients may not be able to reach their premorbid activity levels. Voluntary and willful shoulder instability leading to failure of operative intervention has certainly been problematic; the solution has been to try to recognize these situations before operative intervention.[22, 53]

Reasons for failure after posterior instability surgery can be categorized into four main groups, as follows[96] :

  • Group 1 - Traumatic causes of failure, including major trauma and repetitive microtrauma.
  • Group 2 - Nonsurgical causes of misdiagnosis and patient selection errors; misdiagnosis errors may include missed multidirectional instability, incorrect assessment of instability direction, glenohumeral degenerative joint disease, impingement syndrome, cervical spine pathology, and acromioclavicular joint arthritis; selection errors include choosing patients with willful dislocations, problematic psychiatric history, poor motivation, or seizure disorder or selecting patients who are noncompliant with rehabilitation
  • Group 3 - Surgical errors, including uncorrected pathology, overtightening, bone block malposition, osteotomy error, and nerve injury
  • Group 4 - Rehabilitation errors

Long-Term Monitoring

After immobilization, ROM exercises are started. The patient is encouraged to actively move the shoulder. Passive and (particularly) active assisted motion is discouraged for fear of stretching the arm too far, thereby producing recurrent instability. The strengthening program typically is initiated after painless passive ROM is achieved. The strengthening program used is identical to that employed for nonoperative strengthening, as previously described.

Noncontact sports are allowed after 6 months. Contact sports with a brace are allowed after 12 months, with protection of the shoulder in a brace for an additional year.

 

Guidelines

ACR Imaging Criteria for Shoulder Pain

The American College of Radiology (ACR) has published appropriateness criteria for imaging of both traumatic[97] and atraumatic[98] shoulder pain.

Radiographs of the shoulder are the most appropriate initial imaging study in either traumatic or atraumatic shoulder pain. Either magnetic resonance (MR) arthrography or magnetic resonance imaging (MRI) of the shoulder without intravenous (IV) contrast should be performed for atraumatic shoulder pain when instability and labral tear are suspected and initial radiographs are normal or inconclusive. In patients with traumatic shoulder pain, if physical examination and history suggest a prior dislocation event or if there is instability and radiographs are normal, then MRI of the shoulder without IV contrast and MR arthrography are both appropriate studies.