Abstract

When treating posterior instability knowledge of risk factors that predispose a patient to develop this condition, possible mechanisms of injury, and how to diagnose it via physical examination and imaging are key. Cases presenting on the different places on the subluxation to dislocation spectrum, caused by either repetitive microtrauma, acute trauma, a cause altogether atraumatic, or some combination there of each require slightly different approaches and for different options to be considered. Diagnostic imaging and provocative examination maneuvers for posterior instability will be discussed at length given their significance to the formulation of an effective treatment plan.

Keywords: epidemiology, history, imaging, mechanism of injury, MRI, physical examination, posterior instability, radiograph, risk factors.

Introduction

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  An injury to the shoulder may result in posterior shoulder instability, which ranges in severity from subluxation to dislocation.

  
  
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  The incidence of unidirectional, posterior instability in young athletes is 10%.

  
  
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  Posterior shoulder instability results from repetitive microtrauma, an acute traumatic event, or may be atraumatic.

  
  
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  The most common presenting complaint is either generalized shoulder pain or deep pain in the posterior shoulder.

  
  
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  Provocative examination maneuvers described for the assessment of posterior shoulder instability include the jerk test, Kim test, posterior stress test, and load and shift test.

  
  
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  Diagnostic imaging required in the evaluation includes plain radiographs and magnetic resonance imaging.

The large range of motion allowed by the shoulder joint predisposes it to injury, particularly at the extremes of motion ( ). An injury may result in posterior shoulder instability, which ranges in severity from subluxation to dislocation. A subluxation occurs when translation of the glenohumeral joint occurs beyond physiologic limits with some glenohumeral contact maintained ( ). In contrast, a dislocation occurs when translation of the glenohumeral joint occurs such that there is no residual contact between the humeral head and the glenoid fossa ( ). The diagnosis of shoulder dislocation requires radiographic evidence of complete disassociation of the humeral head and glenoid or the need for a manual reduction of the joint. Shoulder subluxation has been reported to account for 85% of traumatic, anterior shoulder instability events. However, shoulder subluxation events are often underreported because the diagnosis is not as straightforward as the diagnosis of a shoulder dislocation.

Epidemiology

Posterior shoulder instability most often presents in 15- to 40-year-old athletes ( ). The incidence of unidirectional, posterior instability in young athletes is 10% ( ). The reported incidence of posterior shoulder instability has increased as the understanding of the pathoanatomy and awareness of this diagnosis increased over the past decade ( ). Although unidirectional posterior instability events can present as dislocation, more than 90% of these events are subluxations. More than 50% of patients present with recurrent, rather than first-time, subluxations.

Risk Factors

Patients with seizure disorders, a history of alcoholism, and those who sustain an electrical shock are at risk for a posterior shoulder dislocation ( ). More commonly, the young, athletic population has been identified at risk for developing recurrent posterior shoulder instability that manifests as recurrent shoulder subluxation rather than dislocation ( ). Athletes who have been identified to be at risk for developing posterior instability include weight lifters, football linemen, overhead throwers, rugby players, paddling sport athletes, swimmers, volleyball players, gymnasts, and climbers ( ). More recently, batters have been identified to be at risk for developing episodic subluxation of the lead shoulder during the baseball swing ( ). Other activities that generate repetitive, posteriorly directed forces in the shoulder include archery and riflery, and wheelchair use also predisposes participants to developing posterior shoulder instability ( ).

Anatomic characteristics that predispose patients to recurrent posterior instability include increased glenoid retroversion ( Fig. 2A.1 ) ( ). A prospective evaluation of young athletes with posterior instability revealed that the most significant risk factor for posterior instability is increased glenoid retroversion. In their cohort, the median version in the noninjured participants was −7.7 degrees compared with −17.6 degrees in the participants with posterior instability ( ).

Axial T2-weighted magnetic resonance arthrogram image of the glenohumeral joint demonstrating excessive retroversion secondary to glenoid dysplasia.

Mechanism of Injury

Posterior shoulder instability results from repetitive microtrauma or an acute traumatic event, or it may be atraumatic ( ). Patients who participate in activities in which the shoulder is repetitively posteriorly loaded in a flexed and internally rotated position are at risk for developing posterior shoulder instability. Over time, the cumulative microtrauma results in attenuation and tearing of the posterior capsulolabral complex and the posterior band of inferior glenohumeral ligament (PIGHL), which results in posterior instability ( ).

An acute onset of posterior shoulder instability often results from a specific traumatic event. The classic traumatic event that results in acute, traumatic unidirectional posterior instability involves a posteriorly directed force that is applied to an adducted, internally rotated, and forward flexed upper extremity ( ). This results in shearing force of the humeral head along the glenoid that results in detachment of the capsulolabral complex. Acute, traumatic events generally predispose patients to recurrent instability ( ). Similar to traumatic, anterior shoulder instability, the initial instability event in traumatic, posterior instability is most commonly a subluxation event rather than a dislocation ( ).

Atraumatic posterior instability generally occurs in patients with generalized laxity ( ). Initially, instability symptoms are brought on by activities that posteriorly load the shoulder. As the tissues become more attenuated, these patients begin to have symptoms with activities of daily living.

Pathoanatomy

Posterior shoulder instability has been associated with injury to the osseous and soft tissue stabilizers. The congruity and stability of the shoulder joint depend on the soft tissue stabilizers because of the significant mismatch between the radius of curvature of the glenoid and humeral head (Lugo et al, 2008; ). The maximal area of the humeral head that articulates with the glenoid is 30%. Although the stability from the glenoid and humeral head alone is inadequate, the osseous anatomy of the shoulder plays a critical role in the overall stability of the shoulder. Increased glenoid retroversion has been demonstrated to predispose patients to loss of containment and resulting atraumatic posteroinferior instability ( ). Glenoid bone loss and glenoid dysplasia have also been associated with shoulder instability ( ). Operative intervention for posterior shoulder instability that does not address glenoid bone loss or dysplasia is at risk for an unsatisfactory result ( ).

The soft tissue stabilizers of the shoulder include static and dynamic soft tissue stabilizers (Lugo et al, 2008; ). The static stabilizers include the labrum, joint capsule, and glenohumeral ligaments. The glenoid labrum is a rim of fibrocartilaginous tissue that is attached to the periphery of the glenoid effectively increasing its depth by 50%, thereby increasing the contact area at the glenohumeral articulation. The labrum also allows for a negative-pressure suction phenomenon to occur that contributes to the overall stability of the shoulder joint. Nondisplaced posterior labral lesions, which are known as Kim lesions, are also associated with posterior instability ( Fig. 2A.2 ) ( ). These tend to occur in athletes who have repetitive microtrauma and who subject the shoulder to repetitive loads with the arm in adduction and internal rotation, such as swimmers. The labrum is attached to the posterior capsule, and the detached labrum is often found in continuity with the capsule ( ). Additional pathology of the capsulolabral complex that is associated with posterior instability includes a redundant capsule, a tear in the posterior capsule, reverse humeral avulsion of the glenohumeral ligament (HAGL), and fraying of the posterior labrum ( ).

Arthroscopic image of a posterior labrum lesion.

The glenohumeral ligaments primarily function by limiting shoulder motion at the extremes of shoulder motion. In contrast to the anterior capsule and the anterior glenohumeral ligaments, the posterior capsule and the PIGHL are relatively thin ( ). The PIGHL primarily resists posterior translation when the shoulder is placed in the posterior loading position, which consists of internal rotation and forward flexion ( ). Although the PIGHL is the primary resistor to posterior translation, the middle glenohumeral ligament (MGHL) resists posterior translation of the shoulder in midrange shoulder abduction and the superior glenohumeral ligament (SGHL) resist posterior translation in midrange adduction ( ). Injury to or attenuation of the PIGHL results in posterior shoulder instability.

A reverse humeral avulsion of the glenohumeral ligament (RHAGL) lesion has also been identified as a source of posterior shoulder instability ( ). The majority (62%) of these lesions are associated with pathologic findings that may lead to missed RHAGL lesions, resulting in persistent instability. Therefore assessment of magnetic resonance imaging (MRI) for posterior shoulder instability must be carefully scrutinized with a high index of suspicion for this lesion. RHAGL lesions can be partial, complete, or floating, where the glenohumeral ligament is detached from the humerus and glenoid. It is important to note that the presence of a glenoid-based PIGHL lesion (reverse Bankart lesion) does not preclude the presence of a concomitant secondary disruption (RHAGL or capsular tear; Fig. 2A.3 ).

(A) Arthroscopic image of a reverse Bankart lesion in a 21-year-old wrestler with posterior shoulder instability. (B) Further arthroscopic evaluation of this patient’s glenohumeral joint revealed a capsular rent. (C) Arthroscopic image after repair of the combined reverse Bankart lesion and the capsular rent.

The dynamic soft tissue stabilizers include the rotator cuff and the scapulothoracic muscles (Lugo et al, 2008; ). The primary role of the rotator cuff on shoulder stability is to compress the humeral head against the glenoid and to maintain the humeral head in a relatively central position on the glenoid thereby limiting shear stress. The rotator cuff is the most important dynamic stabilizer in preventing posterior shoulder instability ( ). The subscapularis muscle is the primary muscle of the rotator cuff that dynamically resists posterior translation of the humeral head ( ). Injury to or attenuation of the rotator cuff, particularly the subscapularis, may result in posterior shoulder instability ( ).

Concomitant pathology associated with posterior instability events include reverse Hill-Sachs lesions and injury to any of the static and dynamic stabilizers ( ). Reverse Hill-Sachs lesions are humeral head compression fractures that result from impaction of the humeral head on the rim of the glenoid that occurs during a dislocation event. Hill-Sachs lesions that are larger than 1.5 cm ³ are associated with recurrent instability ( ).

History

Because of the high incidence of posterior shoulder instability in young athletes, especially collision athletes and weight lifters, this condition should be considered as part of the differential in athletes presenting with shoulder pain and any suspicion of instability. The history of posterior shoulder instability is often vague, and the onset may not be associated with a specific traumatic event ( ). The most common presenting complaint is either generalized shoulder pain or deep pain in the posterior shoulder ( ). The pain is often associated with decreased strength and endurance ( ). The historical context will depend on the underlying etiology of the posterior instability. Commonly, a young athlete will report a gradual onset of pain and limitation in performance. In acute, traumatic posterior shoulder instability, the athlete will identify a specific event that resulted in a posteriorly directed force applied to an adducted, internally rotated, and forward flexed shoulder. It is often difficult to determine how much underlying repetitive microtrauma preceded this event. In cases of atraumatic posterior shoulder instability, the patient often may present with generalized laxity. Voluntary atraumatic posterior shoulder instability can be positional or voluntary ( ). Voluntary instability that is positional is reproduced by placing the arm in a provocative position (flexion, adduction, and internal rotation). In contrast, voluntary instability that is muscular is more consistent with a muscular imbalance or generalized ligamentous laxity and is reproducible irrespective of the position of the shoulder. A patient who can demonstrate posterior subluxation with muscle contraction (posterior cuff) with the arm at the side may have an underlying psychiatric disorder. Extreme caution is advised in this scenario for any surgical treatment. Care should be taken to elicit history of contralateral instability or similar symptoms, as bilateral involvement can be common.

Physical Examination

The physical examination of a shoulder with suspected posterior shoulder instability should include a comprehensive and systematic evaluation of the shoulder given that the nonspecific symptoms of instability, including generalized pain and decreased strength and endurance, can be attributed to a wide range of etiologies ( ). Examination should begin with a general impression of the function of the patient’s musculoskeletal; system, inspection, palpation, range of motion, neurovascular examination, rotator cuff evaluation, and assessment of stability ( ). Assessment for generalized laxity in the musculoskeletal system is determined by using the Beighton hypermobility scale ( ). It is critical to examine the contralateral shoulder for comparison, paying attention to obvious signs of muscle atrophy, instability, asymmetry, swelling, abnormal motion, and scapular dyskinesia ( ). In posterior shoulder instability, palpation can reveal tenderness at the posterior joint line ( ). Range of motion is often within normal limits with the exception of the overhead thrower population, which is predisposed to having increased external rotation while developing a glenohumeral internal rotation deficit ( ).

Provocative examination maneuvers described for the assessment of posterior shoulder instability include the jerk test, Kim test, posterior stress test, and load and shift test ( ). The jerk test is performed with the patient in a sitting position ( ). The examiner stabilizes the scapula with one hand and uses the other hand to abduct and internally rotate the shoulder by 90 degrees. In this position, the examiner applies an axial load to the abducted and internally rotated arm while simultaneously applying a horizontal adduction force. This test result is positive if it produces a sharp pain. The pain may be accompanied by a posterior clunk or click; however, a test result is positive if it produces a sharp pain irrespective of a clunk or click.

The Kim test was described for detecting posterior labral lesions of the shoulder ( ). This test is performed with the arm in 90 degrees of abduction. With the patient in a sitting position, the examiner holds the elbow and the lateral aspect of the proximal arm, applies an axial loading force, and elevates the distal arm to 45 degrees while applying an inferior and posterior force to the proximal arm. This test result is positive if this maneuver produces a sudden onset of pain, plus or minus a palpable clunk. It is important to perform this test in a chair with back support and with an assistant to provide counterpressure during axial loading.

The load and shift test can be performed with the patient supine or seated. The examiner holds the arm in 50 to 70 degrees of abduction in the scapular plane ( ). With the other hand, the examiner applies a compressive load to the humeral head within the glenoid and then applies posterior and anterior forces ( Fig. 2A.4 ). The amount of translation that occurs can be graded using the McFarland grading system: grade I is translation limited to the glenoid fossa and grade II is translation that occurs to or beyond the glenoid rim ( ).

The load and shift test can be performed with the patient seated or supine. The examiner holds the arm in 20 degrees of forward flexion and abduction. With the other hand, the examiner applies a load to the humeral head while applying posterior and anterior forces.

The posterior apprehension sign can be elicited in the seated or supine position ( ). The examiner uses one hand to stabilize the scapula and the second hand to apply a force to the arm while it is held in 90 degrees of forward flexion, adduction, and internal rotation ( Fig. 2A.5 ). The test result is positive if this maneuver produces pain or apprehension.

The posterior apprehension sign can be elicited in the seated or supine position. The examiner uses one hand to stabilize the scapula and the second hand to apply a force to the arm while it is held in 90 degrees of forward flexion, adduction, and internal rotation. The test result is positive if this maneuver produces pain or apprehension.

Imaging

Routine plain radiographs should include anteroposterior, scapular Y, and axillary lateral views ( ). Although the plain radiographs are generally normal, the axillary lateral view provides the most relevant information for diagnosing posterior shoulder instability ( ). The axillary view can reveal reverse Hill-Sachs lesions, glenoid dysplasia, excessive glenoid retroversion, and sometimes even translation of the humeral head relative to the glenoid ( ). Computed tomography should be obtained to evaluate glenoid version and bone loss in suspicious cases ( Fig. 2A.6 ) ( ). MR without contrast performed with an MRI scanner that has at least a 1.5-Telsa magnet should be obtained to evaluate the soft tissue static and dynamic stabilizers ( ). MR arthrograms have been demonstrated to have a higher sensitivity for detecting labral tears ( Fig. 2A.7 ) and RHAGL lesions compared with MRI without contrast and can be helpful in chronic situations ( ). Obtaining an MRI or MRA is critical for identifying soft tissue pathology that is contributing to the instability and for surgical planning.

Axial computed tomography image of the left shoulder demonstrating excessive retroversion.

Axial T2-weighted magnetic resonance arthrogram image of the glenohumeral joint demonstrating a posterior labrum lesion.

Abstract

Techniques for posterior shoulder instability repair and reverse humeral avulsion of the glenohumeral ligament (HAGL) lesion repair have advanced from traditional open techniques to all arthroscopic techniques with superior outcomes. The use of low-profile, knotless anchors allows for a seamless repair while minimizing the risk of knot impingement. Current techniques of repair have resulted in excellent outcomes, with more than two thirds of athletes returning to their preinjury level of function and greater than 80% of patients reporting good to excellent clinical outcomes.

Keywords: HAGL lesion, humeral avulsion of the glenohumeral ligament, labrum repair, outcomes, posterior glenohumeral instability, posterior labral tear, recurrent posterior subluxation.

Surgical Repair and Technique

Arthroscopic Posterior Labral Repair

See Video 2B.1 .

• Video 2B.1
  

  Posterior Labral Repair

Patient Positioning and Room Setup

We prefer to perform the procedure with the patient in the lateral decubitus position. This position allows the arm to be placed in gentle abduction (45 degrees) and slight forward flexion (20 degrees) with 10 to 15 lb of traction, giving excellent access to the posterior joint and capsule. After induction of general anesthesia and placement of an interscalene nerve block, the patient is transferred into the lateral decubitus position and held in place with an inflatable beanbag. Care is taken to ensure that all bony prominences are well padded, and an axillary gel roll is appropriately positioned under the dependent axilla to prevent an iatrogenic brachial plexopathy. Wide preparation and draping are performed to make sure that easy access to the shoulder both anteriorly and posteriorly is possible. We often angle the bed 45 degrees away from anesthesia machine/anesthesiologist work space and place the visualization tower across the surgical field and at eye level to the surgeon ( Fig. 2B.1 ).

Patient is placed in the lateral decubitus position. The arm is abducted 45 degrees, is forward flexed 20 degrees, and is put under 15 to 20 lb of traction.

Portal Placement

All bony landmarks are marked with a marking pen (the acromion, coracoid process, and acromioclavicular joint). The anterior portal is typically placed in the rotator interval in a trajectory that is diagonal from the coracoid process to the anterolateral edge of the acromion. The posterior portal is created slightly lateral to a traditional posterior arthroscopy portal to allow tangential access to the posterior glenoid for anchor placement. The posterior portal is created first after insufflation of the joint with 30 mL of normal saline, and the anterior portal is created via an “inside-out” technique. Once portals are created a clear cannula is placed in the anterior portal with a traditional dilation technique. Either a 6-mm or 7-mm cannula can be used for the anterior portal.

Diagnostic Arthroscopy

A 30-degree arthroscope placed through a posterior viewing portal is used to perform an initial diagnostic arthroscopy. The joint is checked for concomitant pathology such as superior labral tears, rotator cuff tears, and osteochondral injury. Debridement of the joint can be carried out with a 4.5-mm shaver through the anterior portal as needed. Following an initial diagnostic arthroscopy, the camera is placed into the anterior cannula and the inflow cannula is placed on the side port on the cannula. A switching stick is placed in the posterior portal, which is dilated to 8 mm. An 8.25-mm cannula (Arthrex, Naples, FL) is then placed in the posterior portal. The 30-degree arthroscope can be switched for a 70-degree arthroscope, which allows slightly better visualization of the posterior and inferior capsule and posterior inferior band of the inferior glenohumeral ligament. Surgeons are encouraged to use both 30- and 70-degree arthroscopy cameras to obtain the best visualization possible during capsular and labral repair.

Glenoid and Labrum Preparation

A meticulous glenoid preparation is paramount to the success of the repair. An elevator is initially placed through the posterior portal and the labrum is sharply elevated off the glenoid. The labrum is mobilized as with anterior labral tears until the underside of the capsule edge of the glenoid rim is visualized. Care is taken during labral elevation and mobilization to not transect the labrum, and adequate trajectory through the posterior portal is critical in achieving this goal. If the angle is difficult, the elevator can be brought in through the anterior portal, and the labrum visualized posteriorly. Once adequate mobilization is achieved, a hooded bur is utilized to prepare the glenoid rim. Great care should be used to ensure that the labrum is protected during the bony debridement. A shaver is then utilized to remove any remaining soft tissue debris from the glenoid rim, followed by rasping to create a fresh, bleeding surface conducive to soft tissue healing ( Fig. 2B.2 ).

Complete mobilization of the labrum and glenoid preparation are achieved with a combination of an elevator, rasp, shaver, and bur.

Suture Passing and Labral Repair

We have evolved our technique to a knotless anchor system (2.4-mm biocomposite short PushLock anchors (Arthrex) with 1.3-mm flat braided SutureTape (Arthrex) as our primary fixation method. Knotless fixation superior to the equator of the glenoid may minimize the risk of humeral head chondral injury as well as articular-sided rotator cuff knot abrasion. Furthermore, SutureTape has fixation strength that is superior to FiberWire (Arthrex) and its low profile allows it to lie flat against the labrum, minimizing tear-through and providing excellent reduction without humeral abrasion. The first step in labral repair is predicated on the surgeon’s understanding of the patient-specific pathology and how much strain the patient routinely puts on their shoulder as part of their lifestyle. Patients presenting with symptoms consistent with recurrent posterior subluxation (RPS) and insidious shoulder pain without gross macroinstability may benefit from a primary labral repair without significant capsular plication/advancement (e.g., throwing athletes). Patients with macroinstability or dislocation who participate in high-demand contact sports (e.g., offensive linemen) may require labral repair with plication of the posterior capsule.

For the standard posterior labral repair, we prefer to place anchors from approximately the 6 o’clock to the 11 o’clock position on the glenoid. To achieve positioning of the inferiormost anchor an accessory posterior portal may need to be created 45 degrees tangential to the glenoid. This portal is typically created slightly inferior and lateral to the posterior working portal. While viewing from the anterior portal, we use a spinal needle to localize the correct site of entry for the accessory posterior portal. Once the correct location and trajectory are identified for anchor placement, an accessory 5-mm cannula is introduced into the joint using a traditional Seldinger technique. Great care should be taken on cannula introduction to avoid damage to the axillary nerve, which lies at risk in this area. The anchors are all placed from inferior to superior after suture passage.

A curved suture hook (Spectrum, Linvatec, Edison, NJ) loaded with a No. 0 monofilament suture is placed through the posterior working cannula with the arthroscope placed in the anterior cannula. A bite of capsulolabral tissue is taken slightly inferior and lateral to the level of desired anchor location (to achieve capsular plication and advancement) ( Fig. 2B.3 ), and the suture is delivered through the labrum against the glenoid articular margin. The monofilament suture is shuttled through the posterior working cannula, and a loop of SutureTape is placed in a knot of the monofilament suture. The goal is to create a “cinch” stitch akin to a luggage tag that will reduce the labrum and provide optimum suture security around the tissue. The loop of SutureTape is then shuttled back through the posterior working cannula, and the tail ends of the suture are delivered through the loop created in the tape. The two tails of the SutureTape are pulled and the cinch stitch is reduced to the labrum ( Fig. 2B.4 ). A knot pusher can be used to help reduce the knot to the labral tissue if needed, when there is concern that the tissue is of poor quality. This creates 2.6 mm of SutureTape, because the tape is essentially doubled over to create a stable fixation construct around the labrum and capsular complex. The ends of the tape are delivered through the accessory cannula for anchor placement. The drill guide is then placed through the accessory posterior cannula, and a pilot hole drilled in the desired location. The suture ends are shuttled through the eyelet of the knotless anchor, the anchor is slid to the level of the glenoid, and slight tension is applied to the limbs to reduce the labrum. The anchor is impacted into place within the pilot hole, and the labrum and capsule are reduced to the glenoid margin. Additional anchors can be placed in an identical fashion as needed. Anchors in the 8 o’clock to 11 o’clock position are generally placed through the standard posterior portal, which provides a better angle of approach in this zone ( Fig. 2B.5 ).

A curved suture hook is used to pass a monofilament shuttling suture next to the desired anchor location (note the osteochondral lesion on the posterior humeral head).

A luggage tag loop (“cinch stitch”) made with SutureTape (Arthrex, Naples, FL) is secured down to the labrum.

This image provided courtesy of Arthrex, Inc.

Anchors securing the labrum from the 8 o’clock to the 11 o’clock position (the osteochondral lesion has also been debrided and a microfracture can be performed if clinically indicated).

Posterior Portal Closure

The posterior portal is closed using a No. 1 polydioxanone suture (PDS). The cannula is withdrawn to a level just external to the capsule. A suture passer is then used to pierce the capsule adjacent to the portal, and the PDS suture is introduced into the joint. A penetrating suture grasper is used to pierce the capsule on the opposite side of the portal, and the suture is retrieved. A sliding Weston knot is then used to close down the capsule. Additional sutures can be placed in a wider fashion if additional plication is required by the patient’s needs as predetermined from the preoperative plan.

Rotator interval closure is not routinely performed as part of our technique for posterior instability repair. Indications for rotator interval closure are pathology specific to the rotator interval (capsular tear, injury to the superior glenohumeral/coracohumeral ligament complex) and excessive laxity in patients with multidirectional instability (sulcus sign, etc.). There is concern in the throwing athlete that excessive tightening of the rotator interval may serve to decrease glenohumeral external rotation and could compromise the ability to return to competitive throwing, despite its positive effects on restricting pathologic posterior glenohumeral translation.

Arthroscopic Reverse Hagl Lesion Repair

Patient Positioning, Setup, and Portal Placement

As with posterior labral repair, patients undergoing reverse HAGL lesion repair are optimally treated in the lateral decubitus position. The positioning, room setup, and portal placement are identical to those for primary posterior labral repair.

Diagnostic Arthroscopy

Diagnostic arthroscopy is carried out similarly to that for posterior labral repair. In evaluation of the HAGL lesion, viewing with a 70-degree arthroscope from the anterior portal greatly aids in visualization of both the lesion and the humeral attachment site of the ligament. The reverse HAGL lesion can be identified from the presence of a patulous posterior inferior capsule and the loss of the normal humeral attachment of the posterior inferior glenohumeral ligament ( Fig. 2B.6 ). Either one working posterior portal or an accessory portal can be created in a fashion similar to that already described for labrum repair. Because the posterior capsule is fairly patulous, we have found that a single posterior portal typically gives us adequate access and excellent mobility. The humeral head can be rotated as needed by manipulation of the arm while it is in traction to expose the bare area of the humerus and the normal attachment site of the lesion.

Arthroscopic view from the anterior portal viewing posteroinferiorly of an avulsed reverse HAGL lesion.

Reverse HAGL Repair

After identification of the lesion the posterior humeral head is prepared to optimize the surface for bone to soft tissue healing ( Fig. 2B.7 ). Working from the posterior portal, we use a rasp or bur to freshen the surface of the humeral head and soft tissues to create a bleeding surface amenable to healing.

Preparation of the humeral attachment site for reverse HAGL lesion repair with a bony rasp.

Depending on the size of the lesion, either one or two anchors can be placed within the previously prepared humeral bed. Bone quality determines whether screw-in (rotator cuff style) anchors (4.5-mm double-loaded) or drill-in glenoid style anchors (ranging in size from 2.0 to 3.7 mm [SutureTak, Arthrex]) are placed percutaneously (through a 7 o’clock portal), through an accessory cannula, or through the posterior working portal. We prefer a double-loaded suture anchor to optimize reattachment of the ligament through a broad repair site. For smaller patients, one anchor may suffice; however, for the average size patient two anchors placed in a diagonal fashion adequately covers the defect. A double-loaded suture anchor is then placed into the humeral head at the level of the posteroinferior glenohumeral ligament attachment site ( Fig. 2B.8A ).

(A) Double-loaded anchor placed into the humeral insertion site; sutures are withdrawn out an 8.25-mm cannula docked superficial to the capsule. (B) Ligament is reduced and secured to the anatomic insertion site with a sliding locking knot.

After placement of the anchor(s), the posterior cannula is withdrawn slightly just posterior to or “outside” and extraarticular to the posterior capsule, and the sutures are retrieved with a penetrating suture grasper in a mattress-stitch configuration. Each suture is passed individually to create two mattress stitches at the superior and inferior aspects of the ligament attachment site. While viewing intraarticularly from the anterior portal, we use a sliding locking knot to reduce the ligament and secure it to the humeral head ( Fig. 2B.8B ). The knots are then all tied in successive fashion to complete the repair.

Operative Outcomes

Abstract

Although less common than anterior instability, posterior glenohumeral instability can just as debilitating and challenging to treat. Posterior injuries typically occur in adduction and internal rotation with the primary initial treatment being physical therapy. If conservative means are unsuccessful and posterior instability is recurrent, operative intervention, both arthroscopic and open, is indicated. Open posterior stabilization may allow for a more extensive capsulorrhaphy. In cases of excessive glenoid retroversion, posterior glenoid osteotomy may be effective. Large, engaging reverse Hill-Sachs lesions may call for open osteochondral allograft transplantation. Postoperative management regimens after these procedures are performed are presented as well.

Keywords: glenoid osteotomy, McLaughlin procedure, open posterior capsulorrhaphy, osteochondral allograft transplantation, reverse Hill-Sachs lesions.

Introduction

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  Posterior glenohumeral instability is much less common than anterior instability.

  
  
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  Injuries typically occur with an adducted, internally rotated shoulder.

  
  
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  Physical therapy is the primary initial treatment in most cases.

  
  
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  Operative intervention is indicated in recurrent posterior instability.

  
  
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  Operative options include arthroscopic and open procedures.

  
  
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  Open posterior stabilization may allow for a more extensive capsulorrhaphy.

  
  
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  Posterior glenoid osteotomy may be required for posterior instability in the setting of excessive glenoid retroversion.

  
  
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  Open posterior approach and osteochondral allograft transplantation may be necessary for a large, engaging reverse Hill-Sachs lesion.

Posterior glenohumeral instability occurs much less commonly than either anterior or multidirectional instability. Patients may have undefined and vague symptoms, such as posterior shoulder discomfort, pain, inability to participate in their sports, and repeated subluxation events. Further complexity exists because no single pathologic lesion occurs in all cases of posterior shoulder instability. Posterior shoulder subluxation is often accompanied by various lesions, which may result in instability in multiple directions rather than a single isolated direction. Historically, posterior instability has been reported to occur in approximately 2% to 5% of all cases of shoulder instability ( ). However, the reported incidence of posterior instability in the competitive athletic population is increasing, most likely as a result of greater awareness of the associated pathophysiology and the ability to more reliably diagnose and treat patients with operative procedures ( ). Traumatic posterior shoulder instability that develops after athletic or low-energy trauma represents a unique presentation within the spectrum of cases of posterior instability. Several later studies in specific athletic populations, including active duty military, have reported much higher rates of posterior and bidirectional instability than previously cited. , in their series of 231 military patients who had operative stabilization for glenohumeral instability, reported more than 24% with isolated posterior instability and more than 18% with combined anterior and posterior instability.

One of the challenges of accurately diagnosing patients with posterior instability is that they typically do not complain of positional apprehension as those with anterior instability commonly do. The patient with posterior instability can frequently position the arm and demonstrate a subluxation pattern associated with the arm moving from abduction to forward elevation to adduction. Symptoms may be undefined and vague or patients may complain of an inability to participate or decreased performance in their respective sports. Activities that stress the posterior capsule and labrum, such as pushups, bench press, and blocking in football, can exacerbate the symptoms. Because of this common activity in football, isolated posterior shoulder instability has been increasingly recognized as a clinical problem in collision or contact athletes ( ). The initial mechanism of injury is typically a posteriorly directed force on a forward-flexed, adducted, and internally rotated arm. Although a frank dislocation can occur, posterior shoulder subluxation is more common with athletic injuries. Trauma is usually the precipitating factor in this group, but many patients may have a significant element of joint laxity in both shoulders and, possibly, in other joints as well, predisposing them to subluxation. It was once believed that patients with generalized laxity and complaints of shoulder instability were not candidates for operative management. In the more common current view, glenohumeral instability is a complex concept, with joint laxity a contributing factor, and often an initial traumatic event may result in symptomatic instability. A more thorough discussion of the presenting symptoms, diagnosis, and imaging is found in the previous section of this chapter.

The initial treatment for most patients with recurrent posterior instability is physical therapy. Rehabilitation and strengthening of the dynamic stabilizers of the shoulder joint are the primary focus. This treatment includes primarily strengthening of the external rotators and specifically the infraspinatus ( ). When nonoperative treatment is unsuccessful and recurrent symptoms preclude return to sports or affect daily activities, operative stabilization may be employed. Typically, operative stabilization for posterior glenohumeral instability is indicated for chronic recurrent posterior dislocation of the shoulder that is unresponsive to conservative measures. , more than two decades ago, described posterior shoulder instability as one of the most complex shoulder problems confronting surgeons. The advancement of shoulder arthroscopy over the past 30 years has allowed many procedures that were traditionally performed open to now be addressed arthroscopically, including the treatment of posterior glenohumeral instability. The use of arthroscopic techniques to address posterior labral pathology and capsular redundancy is described in detail in previous sections. The focus of this section is on open operative stabilization of posterior instability.

When surgery is being considered, two factors must be evaluated: (1) the posterior labrum and posterior capsular redundancy and (2) anatomic or structural factors that may contribute to posterior instability, such as increased glenoid retroversion and reverse Hill-Sachs defect of the humeral head. If a posterior labral tear and/or posterior joint laxity is present without anatomic abnormalities, posterior labral repair and capsulorrhaphy may be all that are required. Historically, this was accomplished via an open posterior approach as described later. However, with greater understanding as well as advances in equipment and experience, the use of arthroscopic techniques has become the standard ( ). The arthroscopic technique has several advantages over open stabilization. The joint can be more thoroughly evaluated arthroscopically. Concomitant pathology, including superior and anterior labral tears, rotator cuff tears, and biceps tendinopathy, can be addressed concomitantly via arthroscopic techniques. The incisions are more cosmetically acceptable, and postoperative pain is less severe with arthroscopic techniques in comparison with traditional open surgery. The arthroscopic techniques are described in detail in previous sections.

Open Posterior Capsulorrhaphy

Operative Approach

See Video 2C.1 .

• Video 2C.1
  

  Open Posterior Capsulolabral Repair and Reconstruction

For the posterior capsulorrhaphy, the posterior approach is made via a vertical incision starting at the posterior spine of the scapula and centered over the posterior glenohumeral articulation. Fasciocutaneous flaps are developed, and then the posterior deltoid is split in line with its fibers, ideally along the raphe between the middle and posterior components to expose the posterior rotator cuff ( Fig. 2C.1 ). In a large patient it may be necessary to detach a portion of the deltoid from the scapular spine posteriorly to gain exposure; the detachment can be repaired during the closure. Care is taken to make sure the deltoid is not split more than 5 cm inferiorly to the spine of the acromion to prevent potential damage to the axillary nerve. The axillary nerve exits the quadrangular space, which is bound by the long and lateral heads of the triceps muscles and between the teres major and minor muscles. The axillary nerve must be protected when the deltoid is reflected off the scapular spine during the more extensive approach described later.

Operative view of posterior aspect of right shoulder demonstrating anatomic landmarks marked on the skin. The posterolateral acromion, scapular spine, posterior deltoid, and glenohumeral articulation are identified.

A continuous fascial sheet that spreads across the posterior rotator cuff muscles can make it difficult to expose the intervals between muscles ( Fig. 2C.2 ). The spine of the scapula separates the supraspinatus from the infraspinatus, but their tendons converge as they pass laterally to insert on the greater tuberosity ( Fig. 2C.3 ). The boundary between the tendons is nearly indistinguishable at their insertions. Therefore, separate the supraspinatus and infraspinatus, a line can be drawn from the scapular spine to the posterior aspect of the greater tuberosity, which splits the two muscles and their respective tendons. The innervation of both muscles is via the suprascapular nerve. The nerve courses from anterior to posterior after traversing the suprascapular notch underneath the suprascapular ligament. It then runs along the superior surface of the scapula in the supraspinatus fossa, after which it wraps around the spinoglenoid notch to innervate the infraspinatus. When the posterior glenoid is exposed during the osteotomy described later, the suprascapular nerve and vessels must be identified and protected as they exit the spinoglenoid notch.

The skin is incised exposing the fascia over the posterior deltoid muscle.

The deltoid is split between the middle and posterior segments and retracted to expose the posterior rotator cuff muscles, specifically the infraspinatus and teres minor.

The boundary between the infraspinatus and teres minor may be even more difficult to identify because the two muscle bellies blend together over the body of the scapula. However, at the point of insertion of the teres minor on the humerus, there is usually a distinct bony prominence. This may be traced more medially to split the two muscles. This interval can be developed medially without significant risk of damaging either the suprascapular or axillary nerve. To access the posterior capsule, the infraspinatus and teres minor are carefully reflected off the underlying capsule. A sharp self-retaining retractor then can be used to develop and maintain this interval.

The posterior capsule is then opened in a T-shaped configuration with the vertical limb based laterally and the horizontal limb in the middle of the palpable glenoid face ( Fig. 2C.4 ). Unlike in the Bankart procedure, in which a humeral head retractor can be placed into the joint and hinged on the posterior lip of the glenoid to partially expose the glenoid articular surface, the posterior glenoid anatomy typically precludes similar exposure. However, if a posterior labral injury is present, the capsulotomy should allow adequate exposure to repair the labral injury. The posterior labrum is typically less robust than the anterior labrum. The redundant posterior capsule is separated inferiorly from the teres minor and pulled superiorly. The inferior leaflet is sewn to the lateral capsule, in a “pants over vest” pattern to eliminate the redundancy ( Fig. 2C.5 ). The rotator cuff muscles and deltoid are allowed to resume their normal position when the retractors are removed. The skin is closed in standard fashion.

The interval between the infraspinatus and teres minor muscles is developed to expose the patulous posterior shoulder capsule. The capsule is split in a T shape with the vertical limb lateral and the horizontal limb at the lower portion of the posterior glenoid. The upper leaflet (single arrow) and the lower or inferior leaflet (double arrows) are demonstrated.

(A and B) Diagrammatic representation of the posterior capsulotomy and capsulorrhaphy. The lower leaflet is translated superiorly over the upper leaflet to eliminate the redundancy.

Glenoid Osteotomy

If excessive glenoid retroversion or a large reverse Hill-Sachs is present, a posterior capsulorrhaphy may be inadequate to address the posterior instability. Normal glenoid version in most studies has been reported close to 0 degrees, sometimes with slight anteversion but more often slight retroversion with values typically less than 10 degrees in either direction ( ). The normal version can show great variability, and several studies have shown differences in measurements based on techniques utilized to determine version. Irrespective of the variation in glenoid version, it is clear that increased retroversion can lead to recurrent posterior instability owing to the posterior inclination of the glenoid articular surface. In cases of increased retroversion, a capsulorrhaphy alone may not be effective in maintaining joint stability.

The operative approach for a posterior glenoid osteotomy requires a more extensile exposure. Good visualization of the glenoid neck, including the suprascapular nerve and the glenoid articular surface, is paramount to being able to safely and effectively osteotomize the glenoid. Preoperative three-dimensional (3D) computed tomography (CT) is useful for assessing the true glenoid version and expected amount of posterior opening required to restore stability. Because of the tremendous variation in glenoid version for all shoulders, the procedure is typically considered only in patients who have posterior instability with glenoid retroversion greater than 20 degrees. The CT scan should also be carefully assessed for glenoid dysplasia. Glenoid dysplasia, glenoid hypoplasia, and posterior glenoid rim deficiency are all terms for a spectrum of abnormalities involving bone deficiency of the posteroinferior glenoid rim combined with hypertrophy of the adjacent cartilage. at Duke University found a 14% incidence of glenoid dysplasia in 103 consecutive magnetic resonance imaging (MRI) sessions performed for shoulder pathology. They also noted a higher incidence of posterior labral tears in shoulders with moderate or severe glenoid dysplasia than in shoulders with no or mild dysplasia. Although associated with posterior instability, glenoid dysplasia appears to be an entity distinct from excessive glenoid retroversion, wherein the glenoid bone and the articular surface are angulated posteriorly in relation to the long axis of the scapular body.

The operative approach begins with a curvilinear incision stretching across the scapular spine and curving inferolaterally over the glenohumeral articulation ( Fig. 2C.6 ). Fasciocutaneous flaps are developed to expose the deltoid. The deltoid is sharply released off the scapular spine, with care to ensure that a cuff of tendon is left to allow subsequent repair. The deltoid is released laterally all the way to the posterolateral corner of the scapular spine, and the muscle belly is reflected inferolaterally ( Fig. 2C.7 ). The deltoid innervation, the axillary nerve, is protected as it exits inferior to the teres minor in the quadrangular space. The posterior rotator cuff is exposed in its entirety. However, to obtain better visualization superiorly, the posterior corner of the scapular spine is osteotomized. This bone is later utilized to provide bone graft and maintain the opening wedge glenoid osteotomy as described by .

Operative view of right shoulder prior to extensile posterior shoulder. The anatomic landmarks are identified.

(A and B) Cadaveric dissection of left shoulder with the skin removed demonstrating extensile exposure. The deltoid’s attachment to the scapular spine and posterolateral acromion is shown.

The infraspinatus tendon is now released from its humeral insertion on the greater tuberosity. Developing the interval between supraspinatus and infraspinatus is described previously. The tendon is then reflected medially and separated from the underlying posterior capsule. A capsulotomy is made as described previously. The medial limb of the capsulotomy is extended medially and then reflected from its glenoid insertion. The posterior glenoid is carefully exposed to protect the suprascapular nerve and artery, which emanate from the spinoglenoid notch. It should be noted that in shoulders with significant glenoid retroversion, the posterior angulation results in a shorter neck; therefore the width of the posterior glenoid is decreased, resulting in less bone between the articular surface and the spinoglenoid notch. With the neurovascular structures protected, two threaded guidewires are placed across the glenoid parallel to the articular surface. A humeral head retractor can be inserted into the joint to allow visualization of the articular surface. It is imperative that the guidewires and subsequent osteotomy do not breach the articular surface. Positioning the patient supine on a radiolucent table allows for fluoroscopic assessment and confirmation of guidewire placement.

The glenoid is cut with an oscillating saw along the guidewires 5 to 10 mm medial to the glenoid face and parallel to it while the suprascapular nerve is protected. It is helpful to measure the width of the glenoid on CT preoperatively to estimate the depth of the osteotomy. The surgeon must avoid cutting completely across the glenoid neck. The osteotomy is hinged anteriorly and slowly opened. The degree of correction can be measured on preoperative CT with a goal of restoring the version to neutral—that is, no retroversion. The osteotomy is kept open with a wedge of autograft fashioned from the bone of the posterior scapular previously resected. The osteotomy site is held open with an osteotome, and the graft is impacted into the osteotomy site, flush with the surface of the posterior glenoid. ( Fig. 2C.8 ).

Postoperative CT scan of a left shoulder demonstrating the glenoid osteotomy and version correction.

Once the osteotomy is completed, the posterior capsulorrhaphy is performed as described previously, eliminating the capsular redundancy. The infraspinatus is reattached to its insertion on the humerus. The deltoid is now carefully reattached along the scapular spine and the skin is then closed in routine fashion. Postoperative rehabilitation is the same as for the posterior capsulorrhaphy.

Reverse Hill-Sachs Lesion

With some posterior dislocations the softer humeral head is impacted against the harder posterior glenoid, resulting in an impaction fracture of the anterosuperior humerus, designated a “reverse Hill-Sachs lesion” ( Fig. 2C.9 ). The original description of a Hill-Sachs lesion is a humeral impaction fracture of the posterosuperior humeral head that occurs with an anterior glenohumeral dislocation ( ). A procedure to address a large reverse Hill-Sachs lesion that engages the posterior glenoid may be necessary in some cases. Surgical options include osteochondral allograft transplantation and subscapularis transfer into the humeral defect. The subscapularis tendon transfer (first described by and subsequently called the McLaughlin procedure) is performed through a traditional open anterior deltopectoral approach. Alternatively, the procedure described by for chronic posterior instability, transfer of the lesser tuberosity with the attached subscapularis tendon into the reverse Hill-Sachs lesion, may be used. The osteochondral allograft transplantation is performed through an anterior deltopectoral approach ( Fig. 2C.10 ). Although this surgical approach is not the focus of this section, the related injuries may need to be addressed to eliminate posterior instability.

(A to C) Plain radiograph, axial CT scan, and 3D CT scan showing a reverse Hill-Sachs lesion, the anterior humeral impaction fracture resulting from a posterior dislocation.

(A and B) Postoperative plain radiographs showing osteochondral allograft transplantation into the anterior humeral defect to restore humeral surface integrity.

Postoperative Management

The goal of postoperative rehabilitation is to allow for adequate healing, to restore normal motion and strength, and to allow return to preinjury activities and sports participation. The rehabilitation protocol is broadly separated into four phases: (1) protection, (2) restoration of motion, (3) muscle strengthening, and (4) sport-specific activities. Each of the first three phases is about 4 to 6 weeks in duration, but they should be customized to the individual patient. The last phase may take 1 to 3 months depending on the individual’s sport or activity goals.

Phase 1 (4–6 weeks):

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  Immobilize shoulder in external rotation brace for 4 weeks (can be removed for bathing and exercise; worn on outside of clothes).

  
  
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  Teach postural and positional awareness based on safe zone of stability as determined intraoperatively.

  
  
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  Allow performance of core stability exercises with sling and isometric muscle contraction.

Phase 2 (4–6 weeks):

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  Discontinue sling.

  
  
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  Begin proprioceptive exercises.

  
  
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  Regain scapular and glenohumeral stability.

  
  
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  Perform active-assisted range of motion (ROM) as comfortable (using safe zone as guide).

  
  
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  Avoid combined forward flexion and internal rotation exercises initially.

  
  
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  Progress to and achieve full active ROM before beginning next phase.

Phase 3 (4–6 weeks):

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  Commence minimal weight bearing (below 90 degrees).

  
  
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  Progress to core stability exercises.

  
  
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  Incorporate plyometric training.

  
  
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  Increase proprioception through open and closed chain exercises.

  
  
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  Specifically, the patient is started on a program of resistive exercise with an emphasis on external rotation to strengthen the infraspinatus and teres minor muscles. Forward flexion and internal rotation of the arm in abduction across the body are discouraged until the arm has regained stabilizing strength and there is no apprehension on motion, approximately 6 weeks postoperatively.

Phase 4 (4–12 weeks):

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  Begin strengthening with sport-specific exercises and activities.

  
  
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  Resume activities with the goal of preinjury level or better.