Posterior Shoulder Instability

The Problem

Posterior shoulder instability encompasses a number of clinical conditions ranging from traumatic posterior dislocation, unidirectional posterior instability, and posterior instability as part of a multidirectional instability pattern. Similar to anterior instability initial treatment involves non-surgical modalities to strengthen and stabilize the shoulder. Surgical management addresses clearly identified bone and soft tissue structural causes for ongoing instability in the appropriately indicated patient.

Clinical Presentation

Since posterior shoulder instability encompasses a number of clinical conditions patients may vary in their presentations. An acute posterior shoulder dislocation may present following a seizure or electrocution, requiring a manipulation in order to be reduced, leading potentially to unidirectional posterior instability.

Unidirectional posterior instability is most commonly caused by minor or repetitive microtrauma. This is commonly seen in athletes who have their shoulders driven posteriorly as seen in American football lineman, rugby, weight lifting, and gymnastics. It is also described in rifle use from associated gun recoil. These patients will often describe activity specific instability and posterior shoulder pain. This often progresses to symptoms with everyday life such as pushing open a door. Associated ligamentous laxity and scapular dyskinesia can compound the condition.

Posterior instability as part of a multidirectional instability is often seen in a younger age group and is associated with habitual dislocations. These patients have often been able to ‘pop’ their shoulder in and out with a painless clunk. They may now be presenting because of the development of pain or worsening of the instability. Although largely a muscle patterning disorder, the presence of structural abnormalities, especially capsular laxity and new onset posterior labral tearing, can contribute to worsening symptoms.

Diagnostic Workup

A clear timeline of events from first symptoms to current presentation is extremely important to categorize the patient into the various clinical presentations. This helps identify potential structural abnormalities as well as focus treatment. A patient’s age, handedness, and activity levels both within and outside the workplace are important for the treatment algorithm. As with any instability history, the frequency of both pain and instability episodes should be sought as well as the least amount of activity required to cause symptoms.

Physical examination should begin by noting body habitus and resting scapular position. Inspect for muscle atrophy associated with concomitant nerve or rotator cuff injury. Posterior labral tears can be associated with labral cysts extending into the spinoglenoid notch which can compress the suprascapular nerve causing muscle atrophy and weakness. Inspect full range of movement looking for any scapular dyskinesia or muscle patterning abnormalities. Palpate the shoulder’s bony landmarks as well as the posterior joint line, which is often tender. Test for generalized ligamentous laxity followed by specific shoulder laxity with comparison to the unaffected shoulder. Look for a sulcus sign, anterior apprehension and relocation, but specifically for a posterior instability with the load and shift test and Jerk test. It is important to note the patient’s behavior during the physical exam and distinguish the truly apprehensive patient from a voluntary dislocator. Surgery for habitual dislocators is generally associated with poorer outcomes.

Imaging of the shoulder will often include anteroposterior (AP), scapular Y and axillary plain X-rays which are usually normal but may identify bony abnormalities such as a reverse Hills-Sachs, posterior bony Bankart lesion, or glenoid retroversion or dysplasia. Computerized tomography (CT) with 3-dimensional imaging is best at analyzing suspected abnormalities seen on plain films. A magnetic resonance image (MRI) is the most sensitive test to identify the posterior labral pathology associated with posterior instability. Its sensitivity is increased with the use of intra-articular contrast. A MR arthrogram will identify labral pathology and capsular pathology, such as a reverse humeral avulsion glenohumeral ligament (HAGL) lesion and capsular redundancy. Concomitant injury to the rotator cuff and posterior labral cyst pathology will be visualized as well.

Non–Operative Management

Non-operative management is usually the first mode of treatment. It may also be considered in athletes who will require surgical stabilization but are midseason and need to play through their episodes. Patients should begin a program of at least 4-6 months duration with both activity modification and physical therapy. Therapy focuses on strengthening of the muscular stabilizers of the shoulder, scapular stabilization, as well as proprioceptive exercises. Non-operative management is more likely to be successful in those with muscular patterning abnormalities. However, those with traumatic causes are likely to fail non-operative management and will often require surgical intervention if symptoms persist.

Indications for Surgery

Patients should have an identified osseous or soft tissue lesion. They should have failed non-operative treatment with ongoing posterior pain and instability episodes. The pattern of instability should ideally be unidirectional posterior. Similar to anterior instability, procedures can be thought of as soft tissue procedures (mainly arthroscopic surgery) and osseous procedures (mainly open surgery). Unlike anterior instability where values of glenoid bone loss help dictate the need for osseous procedures of the glenoid or humeral head, no such consensus exists in posterior instability. Fortunately the majority of patients who have posterior labral tears and posterior capsular laxity are indicated for soft tissue procedures to address these deficiencies without need to address minor bony deficiencies.

Surgical Technique

The abnormalities that need to be potentially addressed are posterior labral tears, reverse bony Bankart lesions, reverse HAGL lesions, or reverse Hill-Sachs lesions. Most patients will have a glenoid soft tissue lesion, i.e. labral tear, with or without an osseous lesion. Associated capsular laxity may need to be addressed as well.

Glenoid injuries

Posterior labral tear and capsular laxity

The patient can be positioned in either a lateral decubitus or beach chair position. We prefer a lateral position for labral pathology as traction allows better access for capsular and labral work. The patient is given a regional nerve block and under sedation or general anesthetic a standard shoulder arthroscopy is performed with a posterior viewing portal (Figure 1). An anterior portal is utilized to examine and probe the labrum.

Figure 1.

After a diagnostic arthroscopy is completed preparation is made to repair. An accessory posterior portal, a so called 7 o’clock portal, is made 2 cm lateral and 2 cm inferior to the posterior viewing portal. It is important to position this portal so as to give a good line for proposed anchor placement onto the posterior glenoid rim. Additional portals such as the Port of Wilmington are helpful to gain appropriate line of anchor insertion for the superior portion of the posterior labrum. It is helpful to use a large bore cannula to allow passage of various suture passers and retrievers. To complete the repair you can either view through the anterior portal or remain in the posterior viewing portal. Our preference is anterior portal viewing.

Mobilize the labral and capsule tissue with an elevator to aid reduction and exposure (Figure 2). Prepare the glenoid rim in a similar technique as that described for a Bankart repair with a rasp and burr to provide a bony footprint (Figure 3). We prefer to use knotless anchors avoiding potentially harmful knot stacks. A curved penetrating device which allows suture passage is used (Figure 4). We want to superiorly translate the capsule to reduce the redundancy so we aim to bite tissue quite inferior to the intended anchor site, passing through the capsule and exiting at the glenoid rim collecting the labrum with the pass (Figure 5, Figure 6, Figure 7, Figure 8).

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Figure 6.

Figure 7.

Figure 8.

Repeat this step for the remainder of the length of the tear spacing the anchors 1 cm apart as you move superiorly along the glenoid. (Figure 9, Figure 10, Figure 11). A minimum of three anchors should be placed. The posterior capsular portals can be imbricated when closing as well to further address posterior capsular laxity. This is done by backing out the cannula from the posterior portal and inserting either a spinal needle or suture lasso through the cannula penetrating the capsule while the scope is viewing from the anterior portal. A suture (PDS or # 2 permanent suture) is passed, or a shuttle stitch, and can be placed. The lasso or needle is backed out of the cannula while the suture or nitinol wire remains in the joint. A grasping device is then used to penetrate the capsule on the other side of the arthroscopic portal and brought out the cannula. Arthroscopic knot tying is performed while viewing through the anterior portal.

Figure 9.

Figure 10.

Figure 11.

Posterior bone deficiency, glenoid retroversion

For posterior bone deficiency, arthroscopic techniques are described, but commonly this is performed open. The iliac crest is used as a donor site with a tricortical graft harvested, or allograft can be used. With the patient in a lateral decubitus position a vertical incision is made superior and in line to the posterior axillary crease. The deltoid is split in line with its fibres. The underlying infraspinatus and teres minor is exposed and the neurovascular plane between these two muscles is utilized to identify the posterior shoulder capsule. A t-shape capsulotomy is performed for later capsulorrhaphy. The bone block is introduced onto the glenoid rim and secured with two screws. Capsule repair with inferior over superior limb.

A similar approach is made for glenoid retroversion with greater than 20 degrees being an indication. An opening wedge osteotomy is performed 1 cm from the glenoid surface. It is completed across three quarters of the width of the glenoid neck and care is taken not to fracture through anteriorly. A bone graft, which maintains the pre-planned correction, is then fixed in place with screws or a small plate.

Humeral injuries

Reverse Hill–Sachs

Similar to a large Hill-Sachs in anterior shoulder instability, a reverse Hill-Sachs can be treated by transferring soft tissue or bone into the defect. The original McLaughlin procedure involved transferring the subscapularis into the anterior defect. This was modified by Neer who advocated transferring the lesser tuberosity into the defect. The defect can be filled in this manner or with the use of a humeral head allograft or a partial resurfacing via a subscapularis split. As with a Hill-Sachs deformity, massive defects, especially in the setting of chronic locked dislocations, may require a hemiarthroplasty.

Reverse humeral avulsion glenohumeral ligament

This is very rarely seen and poorly reported on in the literature. Similar to its counterpart in anterior instability, a reverse HAGL can be repaired with open or arthroscopic techniques with suture anchors back to its insertion site on the humerus. However, in comparison to HAGL lesions, reverse HAGL lesions are reliably and more easily addressed with arthroscopy. Humeral avulsion glenohumeral ligament lesions associated with anterior instability are better addressed with open techniques as the location of the tear from the humeral neck makes it difficult to reliably repair it anatomically.

Pearls and Pitfalls of Technique

Setup

The setup for posterior labral repair is critical. Use of the anterior portal for viewing and working via the posterior portals means the surgeon will feel most comfortable and orientated if standing at the head of the bed looking directly down on the shoulder. Standing in a traditional position posterior to the shoulder makes the procedure more difficult and disorientating. It is imperative that before the patient is draped that the table is positioned so the anesthetic equipment doesn’t impose on your working space. Commonly for shoulder arthroscopy the anesthetic equipment and personnel will be at the head of the bed but this will compromise your access for this case. Use of multiple monitors as you change your working position from the posterior aspect of the shoulder to the superior aspect are also very helpful.

Portal position

The position of your accessory posterior portal (7 o’clock portal) is also critical. You should take time to confirm its position with a needle. It needs to accommodate a cannula which will allow for curved suture penetrators to pass down. It should allow these instruments to grasp the capsule and labrum. They should also allow an angle for anchor insertion. This is usually achieved by having the portal lateral and closer to the humeral head than the glenoid to give you the correct line. This is especially important with knotless anchor fixation, which is less tolerant of slight deviations in angle, resulting in anchor or anchor shaft breakage as well as potential articular cartilage injury, as the anchors undermine the cartilage as it is inserted more parallel to the glenoid. The most precise technique involves the use of a long needle that allows a cannulated switching stick to be introduced over it. Cannula dilators should then be used successively to open the portal in a controlled fashion.

Equipment

Tissue penetrators of varying angles should be available as the angle of penetration changes as you move along the posterior glenoid rim. Standard arthroscopy equipment such as shuttling and retrieving devices will be required. A third scrub assistant can be helpful for applying traction especially for the most inferior anchor placement. This person can also be responsible for holding cannulas so they are not continually pulled out of the joint on instrument exchange. Lateral decubitus position offers enhanced views of the posterior labrum not as easily achieved with the beach chair position.

Technique

When elevating the labrum and preparing the glenoid neck, use a tissue grasper at completion to confirm you have adequately mobilized the labrum and capsule. Viewing from the posterior or anterolateral portals can help confirm you have debrided the posterior glenoid rim to bleeding bone. Work inferior to superior and if part of a more circumferential tear, complete your posterior repair first.

Before passing a tissue penetrator through labrum and capsule, picture where you want the entry point on the capsule to be and the likely exit point at the glenoid given the curve on your specific device. This should help avoid making multiple passes and multiple penetrations potentially weakening or tearing the tissue.

Potential Complications

To avoid patient positioning-related complications, you should be comfortable placing the patient in the lateral position with adequate padding of all limbs and the chest to prevent compressive neuropathies. Traction on the arm should rarely exceed 10 pounds.

The most common complications seen are iatrogenic chondral injuries. These occur from disorientation when moving instruments within the joint. This includes insertion of cannulas when switching sticks are not pointed away from the glenoid. They may also be caused from drilling at the wrong angle for anchor placement and also inserting an anchor at the wrong angle leading to subchondral elevation. Anchor breakage can also occur if the anchor is inserted at a different angle to the drill hole, which can lead to a loose foreign body in the joint. Injury to the axillary nerve is rare but the nerve is at risk if too much capsule is captured in the axillary pouch with inferior tissue penetration. The goal is to stay within 1 cm of the glenoid rim at the inferior aspect of the glenoid to prevent axillary nerve injury.

Failure of repair can occur if the labrum fails to heal, either through poor surgical technique or poor tissue quality. Aggressive post-operative rehabilitation or non-compliance with restrictions can also lead to failure. Not identifying all of the pathological lesions within the shoulder and not addressing these sufficiently are other causes for failure. Post-operative stiffness is uncommon with posterior stabilization.

Post–operative Rehabilitation

Phase I (Weeks 0-6)

Sling immobilization at all times (in flexion, abduction, and 0 degrees of rotation): keeps stress off posterior repair except for showering and rehab under guidance of physical therapist (PT). Goal is to avoid internal rotation.

Weeks 0-3

Range of Motion (ROM): None.

Weeks 3-6

• Begin passive ROM: Restrict motion to 90 degrees of forward flexion, 90 degrees of abduction, and 45 degrees of internal rotation

• Therapeutic exercise:

  Elbow/wrist/hand ROM

  Grip strengthening

Starting week 3:

• Begin passive ROM activities: Codman’s, anterior capsule mobilization

• Heat/ice before and after PT sessions

Phase II (Weeks 6-12)

• Sling immobilization for comfort only

• ROM: Begin active assisted range of motion (AAROM)/active range of motion (AROM)

  Goals: 135 degrees of forward flexion, 120 degrees of abduction, full external rotation

• Therapeutic exercise:

  Continue with phase I exercises

  Begin active-assisted exercises – deltoid/rotator cuff isometrics

Starting week 8:

• Begin resistive exercises for rotator cuff/scapular stabilizers/biceps and triceps. (Keep all strengthening exercises below the horizontal plane during this phase: utilize exercise arcs that protect the posterior capsule from stress.)

• Modalities per PT discretion

Phase III (Weeks 12-16)

• ROM: Progress to full AROM without discomfort

• Therapeutic exercise – advance phase II exercises:

  Emphasize glenohumeral stabilization, external rotation, and latissimus eccentrics

  Begin upper extremity (UE) ergometer/endurance activities

• Modalities per PT discretion

Phase IV (Months 4-6)

• ROM: Full without discomfort

• Therapeutic exercise – continue with strengthening:

  Sport/work specific rehabilitation – plyometric and throwing/racquet program

  Continue with endurance activities

  Return to sports at 6 months if approved

• Modalities per PT discretion

Outcomes/Evidence in the Literature

Chalmers, PN, Hammond, J, Juhan, T, Romeo, AA. “Revision posterior shoulder stabilization”. J Shoulder Elbow Surg. vol. 22. 2013. pp. 1209-20.

Hegedus, EJ, Goode, AP, Cook, CE, Michener, L, Myer, CA, Myer, DM, Wright, AA. “Which physical examination tests provide clinicians with the most value when examining the shoulder? Update of a systematic review with meta-analysis of individual tests”. Br J Sports Med. vol. 46. 2012. pp. 964-78. (Review3)

Lenart, BA, Sherman, SL, Mall, NA, Gochanour, E, Twigg, SL, Nicholson, GP. “Arthroscopic repair for posterior shoulder instability”. Arthroscopy. vol. 28. 2012. pp. 1337-43.

Bahk, MS, Karzel, RP, Snyder, SJ. “Arthroscopic posterior stabilization and anterior capsular plication for recurrent posterior glenohumeral instability”. Arthroscopy. vol. 26. 2010. pp. 1172-80.

Pennington, WT, Sytsma, MA, Gibbons, DJ, Bartz, BA, Dodd, M, Daun, J, Klinger, J. “Arthroscopic posterior labral repair in athletes: Outcome analysis at 2-year follow-up”. Arthroscopy. vol. 26. 2010. pp. 1162-71.

Bokor, DJ, Fritsch, BA. “Posterior shoulder instability secondary to reverse humeral avulsion of the glenohumeral ligament”. J Shoulder Elbow Surg. vol. 19. 2010. pp. 853-8.

Engelsma, Y, Willems, WJ. “Arthroscopic stabilization of posterior shoulder instability”. Knee Surg Sports Traumatol Arthrosc. vol. 18. 2010. pp. 1762-6.

Munro, W, Healy, R. “The validity and accuracy of clinical tests used to detect labral pathology of the shoulder–a systematic review”. Man Ther. vol. 14. 2009. pp. 119-30. (Review.)

Saupe, N, White, LM, Bleakney, R, Schweitzer, ME, Recht, MP, Jost, B, Zanetti, M. “Acute traumatic posterior shoulder dislocation: MR findings”. Radiology. vol. 248. 2008. pp. 185-93.

Savoie, FH, Holt, MS, Field, LD, Ramsey, JR. “Arthroscopic management of posterior instability: evolution of technique and results”. Arthroscopy. vol. 24. 2008. pp. 389-96.

Summary

Posterior shoulder instability presents commonly after repetitive microtrauma to the shoulder. It is usually insidious in its onset but may present following a specific traumatic event. Various soft tissue and osseous lesions have been described and are associated with posterior instability. Non-operative management is initially indicated followed by arthroscopic repair if symptoms persist. Patient selection along with careful identification and treatment of all pathology will lead to predictable surgical outcomes.

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