Posterior Instability: Arthroscopic Labral Repair/Capsulorrhaphy

Benjamin B. Rothrauff

Justin W. Arner,

James P. Bradley

INTRODUCTION

Posterior shoulder instability has become increasingly recognized as a distinct and important subcategory of shoulder instability with a higher incidence than historically reported. While posterior shoulder instability incidence has historically been cited as 10% to 12% of shoulder instability events,¹ posterior capsulolabral damage at the time of arthroscopy for shoulder instability has been found to equal or even exceed anterior capsulolabral pathology.² Underestimation of the incidence of posterior shoulder instability is in part due to its often subtle signs and symptoms on presentation. Unlike anterior instability, which is generally associated with a traumatic event and a resulting chief complaint of instability, posterior glenohumeral instability is more often caused by repetitive microtrauma to the posteroinferior capsulolabral complex, producing vague and variable complaints, generalized shoulder fatigue, and pain without a specific injury.³ Management of patients with posterior shoulder instability can be challenging due to this difficulty with diagnosis, a variety of surgical techniques available, and lack of consensus regarding management when posterior bone loss is present. While nonoperative management is the first line of treatment, patients with symptoms refractory to conservative measures quite consistently benefit from operative intervention. Posterior glenohumeral stabilization has evolved from open to arthroscopic and anatomic techniques, which have demonstrated reliable and good clinical outcomes, high patient satisfaction, high rate of return to sport, and low complication rates.⁴^,⁵ This chapter details our preferred arthroscopic capsulolabral repair for posterior shoulder instability.

INDICATIONS

Indications for arthroscopic capsulolabral repair for posterior shoulder instability are patient specific, as many patients can be managed successfully without surgery, depending on their activities and goals. A sufficient trial of rehabilitation includes avoidance of aggravating activities, restoration of a full range of motion (ROM), and shoulder strengthening with particular emphasis on the rotator cuff, posterior deltoid, and periscapular musculature. While there remains no consensus on what constitutes failure of conservative treatment, a period of 6 months of physical therapy before consideration of surgical treatment has been proposed.⁶ While rehabilitation can often diminish the functional disability and pain associated with posterior shoulder instability, recurrent subluxation seen in this pathology may persist. A large labral tear or flap tear on magnetic resonance imaging (MRI) or arthrogram (MRA), chondrolabral retroversion of greater than 10°, reverse humeral avulsion of the glenohumeral ligament (HAGL) or discrete posterior capsular tear, or a reverse osseous Bankart lesion, may decrease the likelihood of success with conservative measures, prompting the surgeon and patient to sooner consider surgical intervention. Regardless, if symptoms persist despite a sufficient trial of rehabilitation, operative repair may be offered.

CONTRAINDICATIONS

Contraindications to isolated arthroscopic posterior capsulolabral stabilization also continue to evolve, as emerging studies identify risk factors for failure of arthroscopic repair. Current contraindications to an all-arthroscopic repair include a large engaging reverse Hill-Sachs lesion requiring subscapularis transfer or an osteochondral allograft, a large reverse bony Bankart lesion, excessive glenoid retroversion (type C glenoid), significant osteoarthritis, failure of prior arthroscopic stabilization (relative contraindication), patients with muscular voluntary instability and underlying psychogenic disorders, and patients unable or unwilling to comply with postoperative limitations. In those with extensive glenoid bone loss or poor soft tissue quality, a posterior bone block augmentation, typically iliac crest autograft or distal tibia allograft, can be considered. Ongoing research seeks to elucidate what constitutes critical bone loss that necessitates posterior bone block augmentation.⁷

PREOPERATIVE PREPARATION

History

While posterior shoulder injuries can present with obvious traumatic or locked posterior shoulder instability, athletes most frequently have pathology secondary to repetitive microtrauma leading to recurrent posterior subluxation (RPS). RPS tends to affect a subset of athletes, including overhead throwers, such as baseball hitters, golfers, tennis players, butterfly and freestyle swimmers, paddling sport athletes, weightlifters, military service members, and contact athletes such as rugby players and American football lineman.³ Repetitive microtrauma inherent in these sporting activities can produce posterior capsular attenuation and posterior labral tears ultimately resulting in symptomatic RPS. Regardless of sport, patients with RPS often have vague and ambiguous complaints of diffuse pain and shoulder fatigue without a distinct complaint of instability, making this diagnosis difficult and in contrast to the more primary complaint of instability accompanying anterior shoulder instability.

Despite a similar presentation of signs and symptoms, throwers have a unique mechanism of posterior shoulder injury that involves an avulsion of the posterior capsulolabral complex or a labral flap tear. RPS in throwers can be caused by several mechanisms with a common pathway involving deceleration and eccentric loading during the throwing cycle, leading to repetitive microtrauma. Throwers commonly have a tight posterior inferior capsule (GIRD, glenohumeral internal rotation deficient), which leads to repetitive microtrauma after ball release, and thus progressive tearing occurs. Similarly, throwers are prone to develop superior labrum anterior posterior (SLAP IIb) tears with continued stress on the tension band causing posterior extension along the labrum resulting in RPS. A more dynamic pathology involves an imbalance of a weak or contracted pectoralis major muscle, which allows the latissimus to pull the humeral head posteroinferiorly. Mechanical symptoms or pain during follow-through is the typical complaint in this patient cohort. Like other athletes, instability is not the predominant issue. In those with a dynamic muscle imbalance, pain is typically seen at or just before ball release.⁸

Physical Examination

A comprehensive physical examination is crucial given the breadth of presenting complaints and pathology associated with posterior shoulder instability. Examination should proceed in an organized stepwise fashion, starting with a global assessment of the patient’s kinetic chain, including proximal and distal kinetic chain segments. An assessment of scapulothoracic motion is important, as scapular winging can function as a compensatory mechanism to prevent posterior subluxation of the humeral head in patients with posterior instability by anteverting the glenoid.

Examination of the shoulder should include inspection, palpation, ROM, strength testing, and provocative testing, with reference to the contralateral side. Inspection begins with gross assessment of muscular atrophy, shoulder asymmetry, and scapular dysrhythmia. More specifically, a posterior subacromial “dimple” or skin-tether is associated with posterior positional shoulder instability. Tenderness or crepitus with palpation of the posterior joint line may indicate capsulolabral tearing, synovitis, and/or posterior rotator cuff tendonitis from recurrent episodes of posterior instability.

Shoulder ROM should be assessed bilaterally, including forward flexion, abduction in the scapular plane, external rotation with the arm at the side, and internal rotation with the arm behind
the back, best accomplished with the patient standing. Internal and external rotation of the glenohumeral joint should also be assessed in the supine position with the shoulder abducted to 90° and the scapula stabilized by the examination table. The summation of total internal and external rotation measurements constitutes the total arc of motion, which is essential to evaluate in the throwing athlete. A 25° difference in internal rotation between sides is suggestive of GIRD, and objective parameters of GIRD have been described as greater than 8° deficit in total arc of motion, glenohumeral rotation deficit greater than 20°, and/or more than 5° increase in external rotation compared with the contralateral side.⁹ It is particularly important to assess for total arc of motion and GIRD in throwing athletes, as contraction of the posteroinferior capsule alters the center of rotation of the humeral head to a more posterosuperior location in the position of abduction and external rotation, therefore increasing the risk of posterosuperior pathology. Pathologic GIRD has been associated with microinstability from rotator-interval laxity, which can lead to posterosuperior labral tears and progression of SLAP tears to type VIII SLAP tears with resultant posterior shoulder instability.⁹

Strength testing of both shoulders is performed with a focus on the rotator cuff musculature. Subtle rotator cuff weakness is not uncommon in patients with RPS, as the rotator cuff provides dynamic stability to the posterior shoulder. Supraspinatus strength is assessed with the arm in 90° abduction in the scapular plane with downward force applied to the arm. The strength of the posterior rotator cuff muscles, including the infraspinatus and teres minor, is, respectively, evaluated by resisted external rotation with the elbow flexed to 90° and the shoulder adducted at the side or abducted to 90°. Subscapularis strength is assessed by resisted internal rotation via the lift-off, belly press, and bear hug tests.

Tests for evaluation of posterior glenohumeral instability are described in Table 41-1 and include the load and shift, Kim, jerk, and posterior stress tests. A combination of maneuvers makes up the “Pitt 3 Pack,” as described in Table 41-2, and include the dynamic posterior instability test (D-PIT), Whipple, and O’Brien tests (Figure 41-1). The D-PIT alone was found to be 94.4% sensitive and 95% specific for a posterior labral tear.¹⁰ Generalized ligamentous laxity should also be assessed using the Beighton scale, as this may contribute to multidirectional instability (MDI). Positive impingement signs on examination are often associated with scapular dyskinesia or secondary impingement syndrome from repetitive stress to the posterior rotator cuff muscles. Inferior instability can be assessed by the sulcus sign (with a grade of 3+ that remains 2+ in external rotation being pathognomonic for MDI) and the Gagey test.

TABLE 41-1 Provocative Tests for Posterior Instability

Test	How to Perform	Interpretation of Results	Sensitivity	Specificity
Load and shift test	Patient in supine position Arm in 90° abduction, neutral rotation Axial load applied with anterior and then posterior force to shoulder Translation of humeral head over glenoid rim is graded from 0 to 3+	Posterior load and shift over the glenoid rim indicative of component of posterior instability Inferior translation often associated with posterior subluxation and can be indicative of MDI	37.5%	89.2%
Sulcus sign	Patient in seated position Arm adducted at side, neutral position Downward traction applied	Sulcus sign represents excessive inferior translation of humeral head Suggests inferior instability, possible involvement of IGHL	28%^a	97%^a
Jerk test	Patient standing or seated position Examiner stands on affected side with elbow in one hand, distal clavicle and scapular spine in the other Arm in flexion and internal rotation Flexed elbow is pushed posteriorly while shoulder girdle pushed anteriorly	Pain and sudden jerk indicate positive test as the subluxated humeral head relocates into the glenoid fossa	73%97%^b	98%
Kim test	Patient in seated position Arm in 90° abduction in scapular plane Examiner holds elbow in one hand, lateral aspect of proximal arm in the other hand While elevating the patient’s arm to 45°, a downward and posterior force is applied to the upper arm	Sudden onset of pain indicates positive test, signifying posteroinferior shoulder instability	94%97%^b	80%
Posterior stress test	Patient in seated position Arm held in 90° forward flexion, adduction, and internal rotation Examiner stabilizes medial border of scapula and applies posteriorly directed force to the arm	Apprehension, subluxation, dislocation, or reproduction of pain indicates positive test	Not reported	Not reported
Circumduction test	Patient standing, examiner behind patient Elbow in full extension, arm in 90° forward elevation and slight adduction Examiner applies posteriorly directed load Arm then circumducted with combination of abduction and extension until head reduces into glenoid fossa	Palpable clunk as humeral head reduces into glenoid fossa indicates positive test If no pain or guarding with positive test, often indicates chronic posterior instability	Not reported	Not reported
Modified dynamic labral shear test	Patient standing Arm in 110° abduction and external rotation in the scapular plane, then moved to 70° abduction in the scapular plane	Posterior joint line pain indicates positive test as the labrum is sheared between the humeral head and the glenoid during an internal impingement motion	72%	98%
IGHL, inferior glenohumeral ligament; MDI, multidirectional instability.
^aSensitivity and specificity for inferior instability; not specifically reported in the literature for posterior instability. ^bSensitivity of Kim test increases to 97% when combined with positive jerk test.

TABLE 41-2 “Pitt 3-Pack” Tests for Posterior Instability

Test	How to Perform	Interpretation of Results	Sensitivity	Specificity
O’Brien active compression test	Patient standing or in seated position Arm in 90° forward flexion 10° adduction and internal rotation (thumb pointed down) with elbow in extension Downward force applied to arm Arm then externally rotated and same downward force applied	Deep pain with the arm in internal rotation position that improves with arm in external rotation indicates positive test, which suggests superior labral pathology	94.4%^a	95%^a
Dynamic posterior instability test (D-PIT)	Patient standing Shoulder placed in approximately 135° forward flexion with the elbow in extension (ball-release position) Examiner provides resistance against the arm while the patient continues the throwing motion	Posterior shoulder pain indicates positive test For the modified D-PIT (mD-PIT), the examiner applied pressure to posterior aspect of humeral head to prevent posteroinferior subluxation, thus improving the patient’s pain
Whipple test	Patient standing or in seated position Arm in 90° forward flexion and adduction with hand opposite contralateral shoulder Examiner applies downward force while patient resists	Pain indicates positive test, suggestive of partial supraspinatus tear or superior labrum tear
^aCombination of three positive tests is 94.4% sensitive and 95% specific for a posterior labral tear.

FIGURE 41-1 The Pitt 3-Pack for posterior instability.

A and B, O’Brien, (C) D-PIT, and (D) Whipple test, with performance and interpretation described in Table 44-2.

Imaging

As with nearly all shoulder pathology, initial workup for posterior instability begins with plan radiograph including an axillary view, anteroposterior (AP) view, AP oblique (Grashey), and scapular Y view. While these images will often be unremarkable, subtle features may often be present. Posterior dislocation or subluxation, posterior glenoid bone loss, a posterior bony Bankart fragment, and glenoid dysplasia may be appreciated on the lateral view radiographs when present. The axillary radiograph is particularly helpful in assessing glenoid retroversion, which is an established risk factor for RPS.⁴ Sagittal plane acromial morphology can be assessed on the scapular Y radiographs, and a posterior acromial height (PAH) >23 mm has been associated with a significantly increased risk of posterior instability.

Advanced imaging, most commonly entailing MRI or MRA, is next performed when there is clinical suspicion of posterior instability. MRI findings associated with posterior instability include posterior labral tear or splitting, type VIII SLAP tear, Kim lesion (incomplete posteroinferior labral tears), posteroinferior glenoid deficiency, reverse bony Bankart lesion, posterior translation of the humeral head relative to the glenoid, reverse Hill-Sachs lesion (McLaughlin lesion), flattening of the posterior labrum, posterior labrocapsular periosteal sleeve avulsion (POLPSA), posterior inferior glenohumeral ligament (PIGHL) tear, reverse humeral avulsion of the glenohumeral ligament (rHAGL), Bennett lesion (mineralization of the PIGHL), a posterior capsular tear or rent, increased posterior capsular area, subscapularis tendon avulsion, glenoid dysplasia (lazy J or delta type), or increased glenoid retroversion.¹¹ MRA has been reported to be the most sensitive diagnostic imaging test for detection of posterior labral and capsular lesions¹¹; however, the authors seldom perform MRA and believe MRI provides the appropriate necessary detail. Computed tomography (CT) scans are less frequently performed but can be helpful in patients with posterior glenoid bone loss and/or reverse Hill-Sachs lesions, as well as in those with significant glenoid retroversion, glenoid dysplasia, or abnormal bony morphology. When evaluating osseous morphology and bony defects, it is helpful to obtain a noncontract CT scan with thin slices, three-dimensional reconstructions, and humeral head subtraction views.

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