Introduction

Posterior shoulder instability is less common than its anterior counterpart and remains a challenging problem to diagnose and treat. The indications for open surgical treatment for recurrent posterior instability have changed over the years as arthroscopic techniques have become more refined. A recent meta-analysis comparing nine open studies and seven arthroscopic trials reported no statistical difference in terms of patients’ outcomes.¹

Nonetheless, open surgical techniques remain an important and helpful tool in the shoulder surgeon’s armamentarium when dealing with a patient with posterior instability. In this chapter, we first discuss the necessary preoperative findings, examinations, and imaging techniques that help build our surgical decision making process for open posterior instability surgeries. Second, we discuss our surgical indications and our preoperative planning process. Third, we describe soft tissue and bony procedures designed to address different aspects of posterior instability. Finally, we conclude by discussing our preferred methods for open techniques designed to address posterior instability.

We define the term recurrent posterior instability (RPI) as obvious posterior instability with the discomfort and pain secondary to the humeral head excessively translating posteriorly from the center of the glenoid during active motion. RPI can be caused by repetitive microtrauma leading to recurrent subluxation events and, less commonly, by true posterior traumatic dislocations, which is in distinction to anterior instability.²

The diagnosis of RPI depends on the clinical history of instability, reproduction of symptoms on a clinical examination, and diagnostic evaluation. Only 50% of patients with recurrent posterior instability cite a specific traumatic event that started their symptoms.³ McLaughlin first distinguished posterior (locked) dislocations and RPI.⁴ Patients with posterior instability present much less frequently than those with anterior instability. In the general population, glenohumeral instability can affect 2% of the population, but posterior instability only occurs in 2% to 5% of those patients with shoulder instability.⁵ In this chapter, we focus on the surgical treatment of RPI rather than on the pathogenesis of RPI and the acute and chronic frank posterior dislocations.

Generally, first-line treatment for patients with voluntary or involuntary RPI is focused on physical therapy to strengthen the rotator cuff and deltoid to assist with proprioception training and neuromuscular reprogramming. Burkhead et al published a retrospective review of 87 patients on their rehabilitation protocol for shoulder dislocations (19 shoulders with a history of posterior glenohumeral dislocations) and found that if there is no bone abnormality, then physical therapy can be effective in 83% of patients even when there is capsular hyperlaxity. However, physical therapy had only an 18% success rate for patients with posterior instability resulting from a posttraumatic cause and who have bony defects.⁶ In addition, the relative patholaxity of each individual patient may be a relative indication for open surgical treatment rather than arthroscopic treatment.

Indications/contraindications

Surgical indications for open posterior instability procedures

• Patient with severe cases of posterior instability or pain caused by recurrent subluxation events or dislocations and has failed physical therapy focused on rotator cuff and scapulothoracic strengthening

• Patient must be able to tolerate at least 6 weeks of postoperative immobilization in brace and be able and willing to follow postoperative rehabilitation for the next 6 to 8 months

• Primary cases of patient with voluntary isolated posterior instability with bony deficiencies with a preoperative positive jerk test

• Patients with poor soft tissues and capsular deficiency

• Competitive athletes who wish to return to contact sports and want the least chance of recurrence

• Revision cases after a previous failed arthroscopic procedure

• Surgeon arthroscopic skill level and comfort level with open technique

• Patients with recurrent posttraumatic subluxation and those with involuntary, recurrent, atraumatic subluxation

• Patients with voluntary positional posterior subluxation and a negative past medical history for psychiatric disorders or behavior problems

Preoperative history, examination, and radiographic findings

The path to the correct diagnosis and treatment for the problem begins with a thorough history. If instability occurred after a traumatic event, it is important to learn the position of the arm and direction of force at the time of injury. Patients with posterior instability may describe having their arm in a forward flexed, adducted, and internally rotated position. This may result in a posterior labral detachment or attenuate the capsule allowing later posterior subluxation when performing other activities or sports.

The complaints of patients with RPI may consist of a combination of pain and instability symptoms. In patients that have an atraumatic history, it is important to evaluate for a volitional component and any history or signs of underlying collagen disorder such as Marfan syndrome or Ehlers-Danlos. Patients may have joint laxity or a specific translation for a particular direction or rotation but can be asymptomatic, such as those individuals considered loose jointed. Patients with posterior instability may just complain of pain without symptoms of instability when the arm is placed in the provocative position of shoulder flexion, adduction, and internal rotation.

The pathogenesis associated with RPI can involve the labrum, rotator interval, scapular winging and dyskinesias, capsular redundancy, and problems with the bony anatomy of the glenohumeral joint. Posteroinferior capsuloligamentous hyperlaxity can be due to traumatic (acquired) or congenital causes (e.g., collagen disorders). In most cases, the capsular laxity is the primary cause of recurrent posterior instability; subsequently, posterior instability is often observed in overhead athletes who have recurrent microtrauma when their arms are placed in provocative positions of shoulder flexion, adduction, and internal rotation. Injury to the posterior capsule also can occur in offensive lineman, weight lifters, and boxers with an impact loading mechanism, or with pitchers, tennis players, or swimmers who develop instability symptoms in the follow-through phases of their respective sports. Consequently, treatment options must include rebalancing of the capsular tension and addressing any bony deficiencies. Bony problems may include abnormal joint surface orientation or an osteochondral fracture of the humeral head or glenoid cavity. Instability may result from a change in the orientation of the glenoid to the humerus due to scapular winging and dyskinesias. Some bony causes associated with instability are anterior humeral defects (reverse Hill-Sachs lesions), increased proximal humerus retroversion, and glenoid abnormalities (hypoplasia and/or increased retroversion). It is controversial as to how much impact increased glenoid retroversion has with recurrent posterior instability.⁷^–⁹

In general, patients with symptoms of RPI can be classified according to degree of instability, frequency, direction, and cause. As previously stated, in RPI the degree of instability is a subluxation event and the frequency is recurrent. The direction can be posterior unidirectional or multidirectional defined by the major directional component of instability (i.e., posteroinferior).¹⁰ The cause of RPI can be traumatic or atraumatic, and these groups can be subdivided into patients with voluntary and involuntary subluxation events.

Rare, posterior traumatic dislocations of the glenohumeral joint are associated with seizures, electrocution, and falls with the arm in a forward-flexed, adducted, and internally rotated position. A traumatic inciting event for RPI can come in the form of a blow to the front of the shoulder or an axial loading injury to the arm while the shoulder is flexed. A traumatic event can lead to voluntary and involuntary forms of RPI.

Patients that can voluntarily reproduce their symptoms must be separated into two basic categories: voluntary dislocators and willful, habitual dislocators. Those patients with voluntary RPI describe a subgroup of patients with an underlying conscious or unconscious ability to subluxate their glenohumeral joint. Electromyographic evaluation of these patients demonstrated unopposed activation of the posterior short rotators and posterior deltoid.¹¹ The repeated posterior subluxation events can change initial normal anatomy of the glenohumeral joint and stretch the posterior capsuloligamentous restraints. Vice versa, a patient with voluntary RPI also can develop an involuntary component. Some patients can voluntarily reproduce their posterior instability and have no psychogenic gain from it. Most of these patients do not choose surgical treatment because they do not have enough discomfort to warrant surgery and the increased risk of recurrence.

Willful, habitual voluntary dislocators often have an associated underlying psychogenic disorder. Rowe classified these patients as habitual dislocators and believed that the treatment for these patients should focus on a possible underlying psychogenic disorder.¹² In habitual posterior instability cases, there is an underlying muscle imbalance that allows for willful, voluntary dislocation of the glenohumeral joint when the arm is adducted. These patients are considered poor surgical candidates, and surgery is contraindicated in this group.

Involuntary posterior instability is usually associated with chronic overuse activities that force the humeral head posteriorly and can lead to microtrauma, attenuation of the posterior capsule, and RPI. Examples of these activities include the following: volleyball (motions of the lead arm), overhead throwing (follow-through phase), swimming (pull-through phase), weightlifting (i.e., push-ups, bench press), the backhand stroke in tennis, gymnastics (parallel bars), and straight-arm pass-blocking in American football offensive linemen. The etiology of recurrent posterior instability incorporates the direction of instability (unidirectional versus multidirectional) and scapulothoracic dysfunction, as well as soft-tissue (posterior capsular insufficiency) and bone structural abnormalities (posterior glenoid erosion, anterior humeral head defects).

In these patients, it is important to inquire into the frequency of symptoms, position of the arm with subluxation, and the direction and severity of symptoms. Some patients may complain of insidious pain that can occur later, especially in overhead sports as muscles fatigue in later phases of activities. Muscle fatigue can accentuate dynamic instability. Patients with posterior instability present with complaints of pain alone more frequently than those with anterior instability. Another difference between posterior and anterior instability is that the mechanical symptoms of locking and catching are less common with posterior instability. Additionally, it is critically important to assess if the patient has a volitional posterior instability component.

Examination findings

Posterior instability is associated with subtle examination findings that require an assessment of the active and passive range of motion of both shoulders. First the active and passive range of motion is observed and documented. Usually, patients with posterior instability have normal and symmetric range of motion. Occasionally, palpation of the posterior glenohumeral joint line may be tender or crepitus may be appreciated with internal rotation of the arm. Only in rare circumstances is the strength of the posterior rotator cuff affected by posterior instability. When examining the posterior aspect of the patient’s shoulder, it is important to inspect the patient for any signs of atrophy of the infraspinatus or teres minor.

The nonaffected shoulder and other joints in the body should be examined as well to check for range of motion and generalized ligamentous laxity. Some common physical exams include assessing whether or not the patient can hyperextend the knees and elbows and asking the patient to oppose his or her thumb to his or her ipsilateral forearm. The presence of a sulcus sign (>2 cm of distance from the greater tuberosity to the acromion) is a nonspecific test for multidirectional instability associated with symptoms of pain and symptoms of inferior instability. If the sulcus sign does not decrease with external rotation, the surgeon should consider addressing the laxity in the rotator interval.

The scapula also should be examined to help differentiate scapular winging from posterior instability. In some cases of posterior instability, a compensatory winging can occur, consequently anteverting the glenoid and dynamically increasing bony stability. In addition, it is important to assess scapulohumeral and scapulothoracic motion. Specific posterior instability tests include the following: the posterior capsule stress test, the modified load-and-shift test, and the jerk test (Table 27-1)

Table 27-1 Physical Exam Tests

	Description	Tips
Posterior apprehension	The shoulder is held in 90 degrees of flexion and the humerus is adducted in line with the body with slight internal rotation. A posterior force is directed along the axis of the humerus. A test is positive if the patient has a sensation of posterior subluxation.	The test should reproduce the pain the patient experiences with activity and should be felt posteriorly.
Posterior drawer	With the patient supine, the elbow is flexed to 120 degrees and arm is in 20 to 30 degrees of forward flexion. Various degrees of abduction can be used. The examiner stabilizes the scapula, flexes and internally rotates the arm, and applies a posteriorly directed force to the humeral head in an attempt to translate it over the posterior glenoid rim. Subluxation beyond the glenoid rim that reproduces those symptoms is a positive test.	Make sure the scapula is stabilized for the exam. Always compare the shoulder to the uninjured side to help differentiate between physiologic laxity from patholaxity.
Load-and-shift	With the patient upright, the arm is placed into slight abduction and forward flexion and neutral rotation. The examiner then grasps the proximal humerus and applies a slight axial load, followed by anterior and posterior translational forces. Significant translation can indicate possible instability.	The authors recommend translating both sides alternatively two to three times to help differentiate physiologic laxity from patholaxity.
Jerk	An axial force is applied on the arm in 90 degrees of abduction and internal rotation. The arm is horizontally adducted while maintaining the axial load along the humerus. The arm is then extended to cause the humeral head to reduce back into the glenoid.	This relocation is the same “clunk” that occurs with voluntary instability and indicates a more severe degree of patholaxity.

From Bushnell BD et al: Bony instability of the shoulder. Arthroscopy 24(9):1061–1073, 2008.

Lying supine, the posterior capsule stress test is performed by internally rotating and flexing the patient’s arm to 90 degrees. Next, an axial load is applied on the humerus by pushing the arm posteriorly. In this maneuver, the examiner’s one hand applies a posterior stress to the arm while the other is placed on the posterior aspect of the glenohumeral joint. The test is positive if there is a palpable subluxation of the humeral head over the glenoid rim. This may be uncomfortable for the patient, but pain is not always a specific finding.

The modified load-and-shift test also should be performed with the patient lying in a supine position with the affected arm at the edge of the examination table. The humeral head and proximal humerus are held by the examiner’s one hand while the other one stabilizes the scapula. With the arm held in the plane of the scapula and in neutral rotation, the humeral head is compressed into the center of the glenoid and an anterior and posterior stress is applied.¹⁰ The degree of glenohumeral translation is then graded by the amount of humeral head motion in relation to the glenoid rim. The following is the grading scale: Grade 0 equates to minimal translation, Grade 1 equates to humeral head translation just to the glenoid rim, Grade 2 equates to humeral head motion over the glenoid rim with spontaneous reduction, and Grade 3 equates to humeral head dislocation over the glenoid rim that does not spontaneously reduce.

Radiographic findings

Plain radiographs of the shoulder should include a true anteroposterior view of the glenohumeral joint in neutral, internal, and external rotation; a lateral transscapular view of the scapula or “Y” view; and an axillary view. The impression fracture of the humeral head at the level of the lesser tuberosity, which is characteristically found in patients with a locked posterior dislocation, is rarely seen with recurrent posterior instability. These radiographs can help determine if the glenohumeral joint is located, and if there are any glenoid rim or humeral head fractures. A stress axillary view can be obtained to demonstrate the instability, but this information is usually gained from the history and physical. Dynamic radiographs can help confirm the diagnosis in patients with a volitional component. Most patients with recurrent posterior instability do not have bony abnormalities.

Two other helpful tests are computed tomography (CT) and an MR arthrogram (MRA). A CT is critical to assess the version and morphology of the glenoid and amount of bone loss in revision cases. A CT study can help delineate glenoid morphology and the degree of glenoid retroversion by using axial CT images through the mid-glenoid, which corresponds to the first inferior image on which the tip of the coracoid process is no longer visible.¹³ At this level, normal retroversion is between −2 degrees and −8 degrees. CT studies also can help better quantitate the size of anterior humeral head defects and glenoid fractures. An MRA can help better evaluate a possible injury to the labrum and capsule. The addition of intra-articular contrast to the study helps better identify labral and other intra-articular pathology.

Description of technique(s)

Depending on the injury, diagnosis, and a surgeon’s skill level and comfort level, some injuries can be better addressed through an open surgical approach. Open surgical procedures have been the most common form of treatment for posterior instability when nonoperative treatment regimens have failed. Success with open procedures depends on the surgeon’s preoperative evaluation of the multifactorial aspects of posterior instability in order to correct the pertinent pathoanatomy in each patient’s case. The procedures used to address posterior instability can generally be divided into soft-tissue and bony problems. These procedures include posterior capsulorrhaphy/labral repair with or without a bone block, humerus and glenoid osteotomies, posterior infraspinatus capsular tenodesis, posteroinferior capsular shift, and soft tissue augmentation procedures (e.g., PIGHL reconstruction).

Historically, the results of surgery have been poor with a recurrence rate of up to 50% with significant complications.² Some of the procedures that have been used in the past include the following: (1) subscapularis transfers,² (2) biceps tendon transfers,¹⁴ (3) infraspinatus advancement,¹⁵ (4) reverse Bankart repair, (5) reverse Putti-Platt repair,¹⁶ (6) posterior staple capsulorraphy,¹⁷ (7) rotational osteotomy of the humerus,¹⁸ (8) posterior glenoplasty.¹⁹ We mention these procedures mainly out of historical interest.