AUTHOR AND EDITOR INFORMATION

Section 1 of 12  

• Authors and Editors
• Introduction
• Indications
• RELEVANT ANATOMY
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• Multimedia
• References

INTRODUCTION

Section 2 of 12  

• Authors and Editors
• Introduction
• Indications
• RELEVANT ANATOMY
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• Multimedia
• References

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 readily confirmed with radiographs. The purpose of this article is to review current knowledge about the diagnosis, classification, and treatment of posterior glenohumeral instability.

History of the Procedure

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 that 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 3 of his own patients (and 34 from the literature) that had been diagnosed based purely on 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, 8} Seven of the injuries occurred as a result of trauma, 3 were due to "epileptic convulsions," and 1 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 lift-off test for subscapularis function).

Problem

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).⁹

Hawkins and McCormack described 3 categories of posterior glenohumeral instability, as follows:¹⁰

• 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:¹¹

• 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 nontraumatic injury. It can be subdivided into voluntary and involuntary cases.⁹ The direction of instability also has been used to classify the pathology.¹² 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.¹³ Waters and coauthors, from Boston Children's Hospital, used computed tomography (CT) scanning or magnetic resonance imaging (MRI) to prospectively study 42 patients with birth palsy.¹⁴ 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.¹⁵

Frequency

Recurrent posterior instability of the glenohumeral joint is less common than anterior instability, representing less than 5% of shoulder dislocations in most series.¹⁶ Early in the literature, McLaughlin reported 22 posterior dislocations or subluxations in 581 shoulder dislocations, an incidence of 4%.³ In more recent literature, the incidence rate has been reported to be 2-12% of all cases of shoulder instability.¹⁷

Etiology

Posterior instability is thought to be secondary to 3 types of etiologic processes: a major injury, a repetitive minor trauma, and a virtually atraumatic process.^{18, 16, 19} 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, pectoralis major, and subscapularis muscles overpower the relatively weaker external rotator muscles.²⁰ Pure, isolated, unidirectional posterior subluxation of the glenohumeral joint is rare.^{12, 21} 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.

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, 8, 22, 23} When the bony anatomy is normal, the pathoanatomy often is attributed to the following:

• Excessive capsular laxity
• Loss of integrity of the capsuloligamentous rotator interval (coracohumeral and superior glenohumeral ligaments)^{21, 24, 25}
• Injury to the superior glenohumeral ligament²⁶
• A large capsular recess and disruptions of the glenolabral socket (see Image 1)^{16, 25, 27, 28, 29, 30}

Many authors have emphasized that posterior stability is heavily dependent on the integrity of the inferior glenohumeral ligament.^{31, 32, 33, 20}

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:

• 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^{34, 35}

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 and colleagues reported that imbrication of the rotator interval assists in preventing posterior and inferior instability.³⁶ Selective cutting studies of the glenohumeral joint also have determined the importance of the anterior ligamentous structures on posterior instability.³⁷

Labral injury has been described in association with posterior instability (see Image 2). Pathologic lesions have been identified, such as the posterior labral tear; posterior capsular stripping or laxity; fracture, erosion, sclerosis and ectopic ossification of the posterior glenoid fossa; and reverse Hill-Sachs lesions.³⁸ Labral lesions have also been described in the impact athlete in whom the posterior glenohumeral compressive force is increased.³⁹ This causes a greater resultant shear force imparted to the posterior labrum and articular surfaces with forced translation.

An isolated pathologic lesion responsible for posterior instability is rare. Posterior instability is typically multifactorial in nature, and truly 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.

Clinical

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.¹⁰ 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 (lock out), swimming (pull through), and rowing.¹⁶

Pain is usually limited to the instability episodes, although 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.²¹ Finally, it is important to determine whether the patient has a voluntary type of instability or a positional type of involuntary instability.

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 are often obliterated due to swelling or a large deltoid muscle mass.¹¹ 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.⁴⁰ 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 is typically normal, although patients sometimes have a loss of external rotation with the arm abducted at 90°.²⁰ Testing for generalized ligamentous laxity should be performed. Specific tests for posterior instability include the posterior drawer test (see Image 3). The posterior apprehension test (ie, the jerk test) also can be used. 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 Image 4). 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°.¹⁰

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.⁴¹ The extent of translation during diagnostic examination has been graded as follows^{42, 43, 44}:

• +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), for inferior instability, and through the crank test, for anterior instability—is equally important.^{24, 42, 43, 44}

INDICATIONS

Section 3 of 12  

• Authors and Editors
• Introduction
• Indications
• RELEVANT ANATOMY
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• Multimedia
• References

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 stress 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.⁴⁵ Others have reported that 70% of athletes subjectively improve with a conservative program.^{19, 23} 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 have 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.^{28, 30, 46} Surgical intervention is associated with a 50-95% success rate.^{42, 43, 44}

Children with posterior shoulder instability secondary to neonatal brachial plexus injury fall into 2 general categories: early and late. In children in whom the diagnosis is established early (usually when they are <2 years of age), reconstructive and tendon-balancing procedures are options.^{47, 48} In many children presenting late with established dislocations, rotational osteotomy of the proximal humerus (with or without additional soft-tissue procedures) can significantly improve shoulder function.^{49, 50}

RELEVANT ANATOMY

Section 4 of 12  

• Authors and Editors
• Introduction
• Indications
• RELEVANT ANATOMY
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• Multimedia
• References

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.⁵¹ 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, Butters, and Rockwood described the posterior deltoid-splitting approach to the shoulder.⁵² 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 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.

CONTRAINDICATIONS

Section 5 of 12  

• Authors and Editors
• Introduction
• Indications
• RELEVANT ANATOMY
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• Multimedia
• References

Specific contraindications to the 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 have recommended continuing an exercise protocol for at least 6 months before resorting to surgical treatment. Many patients become asymptomatic in terms of pain and function after completing a physical therapy protocol, although clinically, the instability may persist.^{23, 19}

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.

WORKUP

Section 6 of 12  

• Authors and Editors
• Introduction
• Indications
• RELEVANT ANATOMY
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• Multimedia
• References

Imaging Studies

• Radiographs for dislocations
• • 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 Image 5). Since 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 to 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 due to variations of the beam angle.
• Radiographs for 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 primarily seen in high-level throwers but do not necessarily represent shoulder instability.⁵³ Schwartz and colleagues 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.²⁰
• Computed tomography
• • CT scans also can be used to evaluate osseous involvement, such as glenoid retroversion or hypoplasia and a reverse Hill-Sachs lesion or glenoid rim damage (see Image 6).
  • 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.
• 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 the MRI in identifying posteroinferior labral abnormalities has been questioned, perhaps because of capsular redundancy in this region. In postsurgical cases especially, the usefulness of MRI is limited, and this study is usually not obtained.⁵³
  • MRI can be valuable in the assessment of capsular stripping, bony infractions, and subscapularis avulsion.

Other Tests

• Electromyography and nerve conduction studies
• • Electromyograms 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 litigation cases.

TREATMENT

Section 7 of 12  

• Authors and Editors
• Introduction
• Indications
• RELEVANT ANATOMY
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• Multimedia
• References

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 in the supine position. 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 a painless range of motion, 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 range of motion to perform the activities of daily living.

All patients with posterior shoulder subluxation should undergo a trial of nonoperative care prior to any surgical consideration. An exercise program that develops a pain-free range of motion, 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. The 2-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 3-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). The rigorousness of this program mandates constant monitoring by a physical therapist.

An exercise program is typically 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. 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

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 and colleagues established guidelines for the management of posterior dislocations based on 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).

Closed reduction was recommended if the dislocation was within the previous 6 weeks and if, on axillary radiograph, the articular defect involved less than 20% of the articular surface. If stable, the arm was immobilized in 20° of external rotation for 6 weeks. If unstable, Hawkins and colleagues recommended the Neer modification of the McLaughlin procedure (described below), followed by immobilization. For dislocations that have been present for 6 weeks to 6 months and involve 20-45% of the articular surface, either a McLaughlin or Neer modification procedure would be performed, 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 previously, hemiarthroplasty was recommended.

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. McLaughlin reported good to excellent results in 3 of 3 locked posterior dislocations and 2 of 2 recurrent subluxations. Hawkins and colleagues reported good to excellent results in 4 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%.
• Lesser tuberosity transfer (Neer modification of McLaughlin procedure) - Based on 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 secured with screws. Four of 4 patients in this 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. 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 reported little or no pain, while one, after being symptom free for 6 years, experienced severe dysfunction secondary to avascular necrosis 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 Image 7). 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 when inserting the humeral component.
  
  
  • 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.
  • Pritchett reported that of 7 patients treated with arthroplasty for anterior or posterior chronic dislocation, all improved over their preoperative status, with 5 good results and 2 fair results.
  • Cheng reported that total shoulder arthroplasty for lock 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.

Chronic posterior instability

Due to 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 subscapularis transfers, 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, and combinations of these.

Rowe and Yee described the reverse Bankart procedure in 2 patients, using drill holes placed through the glenoid rim to the medial bone and then securing the capsular flap with mattress sutures. In both of the 2 cases described, the patient regained normal function. The reverse Putti-Platt procedure was originally described by Severin, who shortened the infraspinatus only, and DePalma, who shortened the infraspinatus and teres minor together. The most recent report on this procedure stated that 16 out of 17 patients had excellent results and no recurrent subluxation or dislocation. 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. 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.

In 1967, Scott first described the use of an opening wedge osteotomy to correct excessive glenoid retroversion. 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, Wubben, and Carrera reported good or excellent results in 5 out of 5 patients and recommended iliac crest bone graft instead of bone graft with an osteotomized piece of acromion. Complications following this technique include recurrence of instability, osteoarthritis, avascular necrosis 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.

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 1 of 5 patients. 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 and colleagues.⁶⁴ The authors used this procedure for revision instability repair when posterior glenoid deficiency or retroversion greater than 30° was present.

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. 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. Rotational osteotomy of the humerus has also been described for locked posterior dislocations of the shoulder.

Typical lesions in chronic posterior instability include posterior labral fraying and tears, a patulous capsule, and, rarely, osteoarthritis of the glenohumeral joint (see Image 8). 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, recent procedures have been designed that specifically address this problem (see Images 9-14).

Posterior capsulorrhaphy with suture fixation is currently the open procedure of choice. This treatment was performed with staple fixation in the past; however, staples have caused 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'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 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 and colleagues reported good or excellent results in 28 out of 35 shoulders treated with this technique. Four shoulders became unstable; in 6 of the 7 shoulders in which unsatisfactory results were recorded, previous stabilization attempts had been made. Fuchs and colleagues reported on 26 shoulders treated with this technique and found that it produced very satisfactory intermediate-term clinical results. 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's technique also begins with a vertical skin incision, blunt dissection through the deltoid, and a vertical incision through the infraspinatus tendon, reflecting it medially. If the muscle is particularly lax, the interval between the infraspinatus and 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.

Fronek, Warren, and Bowen described a technique of posterior capsulorrhaphy with or without a bone block for posterior subluxation. 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 and colleagues, 11 patients were treated operatively, with a 91% success rate. 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. Of the 78 patients evaluated, they reported 96% good or excellent results, with recurrent instability reported in 4% of patients (3 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. However, Brems reported poor results in 86% of patients after performing the same technique on shoulders that had undergone previous posterior reconstructive procedures.

Wirth, Groh, and Rockwood described a capsulorrhaphy through an anterior approach for the treatment of a traumatic posterior glenohumeral instability with multidirectional laxity of the shoulder. 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 10 patients treated, 9 had good or excellent results.

Newer 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, Caspari, and Savoie reported the 2-year results on a multiple suture technique for posterior instability. 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 muscle or bone. They reported 17 good or excellent results and 4 fair or poor results. Two recurrent dislocations and 3 subluxations occurred, for an overall recurrence rate of 25%. Wolf reported on 14 patients (with a minimum follow-up of 2 years) who underwent posterior capsular plication with or without suture anchors. Twelve patients had excellent results and 2 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. The mean score on the simple shoulder test improved statistically, as did 2 of the 8 Short-Form 36 (SF-36) parameters. Thirty-five patients had improved stability, and 28 had a perception of residual stiffness.

Bradley and colleagues reported a prospective review of 100 shoulders in 91 athletic patients. 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. In their study, the researchers demonstrated an effective arthroscopic procedure with regard to stability, pain relief, and functional restoration in an athletic population. Subjective stability and pain scale scores improved significantly compared with preoperative values. Functional American Shoulder and Elbow Surgeons (ASES) scores improved significantly, with postoperative range-of-motion mean subjective scores within the satisfactory to full range of motion. 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.

Detachment of the posterior glenoid labrum and capsule below the equator of the glenoid, otherwise known as a posterior Bankart lesion, can be particularly debilitating for patients and challenging for caregivers to effectively manage. A retrospective review of arthroscopically treated traumatic posterior Bankart lesions in 27 shoulders was performed by Williams and colleagues. Capsulolabral repair was conducted arthroscopically, and after a mean follow-up of 5 years, no patient exhibited deficits in range of motion or any instability of humeral head translation beyond the glenoid rim (+1). Ninety-two percent of patients had elimination of pain and instability. Two patients required further surgical intervention; 1 patient ultimately required an open capsulorrhaphy; another patient required a repeat arthroscopy for labral debridement.

Similarly, Kim and colleagues 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. 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 1 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 a variety of shoulder outcome instruments. Follow-up averaged 40 months, and 29 of 31 shoulders rated as excellent or good following surgical intervention. Interestingly, 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 range of motion (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. However, the results of these  instruments did  favor  the  arthroscopic methods of fixation.

Postoperative Details

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 and the DonJoy UltraSling (see Image 15). 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 vary between neutral and 45°, and abduction between neutral and 90°. The common goal is to allow healing through relaxation of the posterior structures.

Follow-up

After immobilization, range-of-motion 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 range of motion 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.

COMPLICATIONS

Section 8 of 12  

• Authors and Editors
• Introduction
• Indications
• RELEVANT ANATOMY
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• Multimedia
• References

Complications associated with posterior glenohumeral instability surgery can be divided into early and late problems. Early problems include incorrect diagnosis, glenoid fracture, humerus fracture, neurovascular injury, infection, and recurrence of instability. Late complications include incorrect diagnosis, recurrence of instability, pain, stiffness, hardware protrusion into the joint, osteoarthritis, infection, and avascular necrosis.

The most common complication following posterior stabilization surgery is recurrence of instability, with rates averaging from 15-20%.^{16, 53} Open and arthroscopic techniques used to treat posterior instability have both been associated with a high recurrence rate when compared 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.^{28, 70}

Reasons for failure after posterior instability surgery can be categorized into 4 main groups, as follows:⁸⁰

• The first group includes traumatic causes of failure, including major trauma and repetitive microtrauma.
• The second group includes the 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.
• The third group consists of surgical errors, including uncorrected pathology, overtightening, bone block malposition, osteotomy error, and nerve injury.
• The final group incorporates rehabilitation errors as the cause of failed instability repair.

OUTCOME AND PROGNOSIS

Section 9 of 12  

• Authors and Editors
• Introduction
• Indications
• RELEVANT ANATOMY
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• Multimedia
• References

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.^{42, 43, 44} 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 1 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 deltoid has  been  damaged.^{70, 28} 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 has recommended that in such situations, reduction of the shoulder joint should be accompanied by release of the pectoralis major muscle and transfer of the latissimus dorsi and teres major muscles.^{47, 48} In older children (Hoffer suggests age 7 years as a possible threshold), rotational osteotomy is an option.

Kirkos and Papadopoulos reported on 22 of their rotational osteotomy patients, ranging in age from 4 to 17 years, with 4 patients demonstrating posterior shoulder subluxation. Improved function in activities of daily living was documented, as were average increases in abduction and rotation of about 25°.⁴⁹ Images 16-18 illustrate the 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. Following rotational osteotomy (see Images 19-20), her function (including the ability to comb her hair) was significantly improved.

FUTURE AND CONTROVERSIES

Section 10 of 12  

• Authors and Editors
• Introduction
• Indications
• RELEVANT ANATOMY
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• Multimedia
• References

Recent advances in arthroscopic techniques hold interesting potential for the management of posterior instability. Long-term studies, however, are not yet available, with most recent reports including follow-up of only a few years. Another area of interest has been thermal capsulorrhaphy for instability of the shoulder. 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. The future may hold some promise for this technique 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.⁸¹

MULTIMEDIA

Section 11 of 12  

• Authors and Editors
• Introduction
• Indications
• RELEVANT ANATOMY
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• Multimedia
• References

Media file 1:  Computed tomography (CT) arthrogram of a shoulder with atraumatic posterior instability demonstrates a patulous posterior capsule consistent with excessive capsular laxity.
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Media file 2:  Arthroscopic examination of a patient with recurrent posterior instability reveals significant fraying and tearing of the posterior labrum.
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Media file 3:  Intraoperative examination under anesthesia of a patient with atraumatic posterior instability demonstrates, via a posterior drawer test, significant posterior subluxation of the glenohumeral joint.
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Media file 4:  Physical examination of this patient with atraumatic posterior instability demonstrates significant posterior glenohumeral translation with the jerk test.
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Media file 5:  Anteroposterior radiograph of this shoulder demonstrates an impression defect in the humeral head; however, the posterior dislocation is not readily apparent on this view.
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Media file 6:  Axial cuts of the postreduction computed tomography (CT) scan demonstrate the anterior impression defect with persistent posterior subluxation of the humeral head.
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Media file 7:  Because this elderly patient also had glenoid arthritis, ultimate treatment was total shoulder arthroplasty.
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Media file 8:  Arthroscopic examination demonstrates significant capsular laxity with a large, redundant posterior recess.
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Media file 9:  The posterior approach to the shoulder begins at the posterolateral border of the acromion and extends to the axilla.
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Media file 10:  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.
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Media file 11:  A Fukuda retractor is inserted to retract the humeral head and expose the posterior glenoid rim.
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Media file 12:  Suture anchors are inserted into the glenoid rim.
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Media file 13:  The sutures are used to perform the capsulorrhaphy and are then tied.
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Media file 14:  Completion of the procedure demonstrates significant reduction of the posterior capsular redundancy.
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Media file 15:  Postoperative immobilization in a gunslinger brace demonstrates appropriate positioning in external rotation.
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Media file 16:  Anteroposterior radiograph of 7-year-old girl with brachial plexus palsy.
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Media file 17:  Scapular-Y view.
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Media file 18:  Axillary view.
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