Arthroscopic Repair of Posterior Shoulder Instability

Steven B. Cohen, Sam G. Tejwani and James P. Bradley

• Posterior instability when compared with anterior instability of the shoulder is relatively uncommon. To diagnose posterior instability, the clinician must take a thorough history and perform a thorough physical examination, in addition to maintaining a high index of suspicion. Nearly 70% of patients will improve with an appropriate rehabilitation protocol. Indications for arthroscopic posterior stabilization include patients with continued disabling isolated posterior subluxation after a rehabilitation program, subluxation with a posterior labral tear, multidirectional instability with a primary posterior component, and voluntary positional posterior instability. Arthroscopic techniques have proven to be 80% to 90% effective at midterm follow-up. Throwing athletes and power athletes are generally able to return to full competition within 9 to 12 months postsurgery. Nonathletes are generally able to return to full activity within 6 to 9 months postsurgery.

Important Points

• Good success rates can be gained by a prolonged course of physical therapy with avoidance of activities in the provocative position.

• Patients with recurrent posterior instability resulting from chronic, repetitive microtrauma or generalized ligamentous laxity tend to respond best to a rehabilitation program.

• Patients in whom conservative measures have failed should be considered for surgical reconstruction.

• Arthroscopic techniques have proven to be 80% to 90% effective at midterm follow-up.

Clinical and Surgical Pearls

• The lateral decubitus position for arthroscopy allows better access to both the anterior and the posterior aspects of the shoulder.

• Placing the shoulder in 10 pounds of traction in the position of 45 degrees of abduction and 20 degrees of forward flexion in effect displaces the humeral head anteriorly and inferiorly, bringing the posterior labrum into clear view.

• The posterior portal is placed approximately 1 cm inferior and 1 cm lateral to the standard posterior portal in patients with demonstrable posterior instability on examination with the patient under anesthesia (EUA).

• We recommend performing rotator interval closure in patients with an inferior component to their instability, as defined by a 2+ or greater sulcus sign that does not improve in external rotation.

Clinical and Surgical Pitfalls

• The use of suture anchors for capsulolabral reconstruction is preferred over suture capsulorraphy alone because it results in a more stable repair.

• Difficulty in the placement of suture anchors can be encountered if the posterior portal is located too far superior or medial in the posterior capsule.

• A spinal needle can be used in positioning the auxiliary portal at the 7-o’clock position on the glenoid and approximately 1 cm lateral to the glenoid rim on the posterior capsule for approach to the posteroinferior glenoid at a 30- to 45-degree angle in the sagittal plane.

Posterior instability, when compared with anterior instability of the shoulder, is relatively uncommon. Reports in the literature state that posterior shoulder instability represents approximately 2% to 10% of shoulder instability cases.1,4,16 Initial attempts to clarify the distinctions of posterior instability were made in 1952 when McLaughlin recognized that differences exist between “fixed and recurrent subluxations of the shoulder,” suggesting that the etiology and treatment of the two are distinctly different.⁴ More than 20 years later, Hawkins reiterated the difference between true dislocations and subluxations and noted that true recurrent posterior dislocations are rare compared with recurrent posterior subluxation (RPS) episodes.⁵ Since that time, additional knowledge has been gained regarding the differences between unidirectional versus multidirectional, traumatic versus atraumatic, acute versus chronic, and voluntary versus involuntary posterior instability. In many respects each of these may represent a distinct form of posterior instability with its own underlying predispositions, anatomic abnormalities, and treatment algorithms.^6–8 Our collective understanding of posterior shoulder instability continues to evolve.

Pathoanatomy

Our understanding of the spectrum of posterior instability has evolved more recently through the study of shoulder injuries in athletes, patients with generalized ligamentous laxity, and patients with posttraumatic injuries. These athletes typically have posterior shoulder instability secondary to repetitive microtrauma, which can occur in multiple arm positions and under a variety of loading conditions. RPS has been observed in overhead throwers, baseball hitters, golfers, tennis players, butterfly and freestyle swimmers, paddling sport athletes, weightlifters, rugby players, and football lineman, among others.9,10 The more common cause of RPS is repetitive microtrauma, most commonly resulting from posterior capsular attenuation and posterior labral tears. Regardless of the type of athlete, patients with RPS often have somewhat ambiguous complaints of diffuse pain and shoulder fatigue without a distinct complaint of instability, often making it tricky to expose the underlying diagnosis and thus the associated pathology.

Acute posterior dislocations typically occur as a result of a direct blow to the anterior shoulder or indirect forces that couple shoulder flexion, internal rotation, and adduction.⁸ The most common indirect causes are accidental electric shock and convulsive seizures, although these are relatively uncommon in the general population. However, recurrent or locked posterior shoulder dislocations from macrotrauma are exceedingly rare in the athletic population.^4,5 The treating physician, because of incomplete radiographic studies and a failure to recognize the posterior shoulder prominence and mechanical block to external rotation, may overlook up to 80% of locked posterior dislocations. Additional pathologic conditions to look for include the following:

• Reverse Hill-Sachs lesion

• Reverse bony Bankart lesion

• Posterior capsular laxity

• Excessive humeral head retroversion or chondrolabral retroversion

• Glenoid hypoplasia

Diagnosis

To diagnose posterior instability, the clinician must take a thorough history and perform a thorough physical examination in addition to maintaining a high index of suspicion. A history of a posterior dislocation requiring formal reduction is more obvious; however patients with RPS may have more subtle findings. The majority of patients with RPS primarily report pain with specific activities, particularly in the provocative position (90 degrees of forward flexion, adduction, and internal rotation),⁸ more often than instability. Knowledge of the athlete’s sport, position, and training regimen is critical in deducing the pathogenesis and specific pathology associated with RPS. Pollock and Bigliani noted that two thirds of athletes who ultimately required surgery had presenting symptoms of difficulty using the shoulder outside of sports, particularly with arm above the horizontal.⁷ An inquiry should also be made regarding mechanical symptoms; one study found that 90% of patients with symptomatic RPS noted clicking or crepitation with motion.¹¹ Often this crepitus can be reproduced during examination and is caused by discrete posterior capsulolabral pathology.

Clinical Examination

• Inspection for skin dimpling, atrophy, and scapular motion

• Active and passive range of motion

• Palpation for tenderness (especially posterior glenohumeral joint)

• Strength testing

• Evaluation for impingement

• Assessment for generalized ligamentous laxity (9-point Beighton scale)

• Stability testing

– Load and shift test for anterior and posterior translation (Fig. 9-1)

Figure 9-1 The load and shift test is performed by placing the thumb and index or long finger around the humeral head, which is then shifted anteriorly and posteriorly.

– Sulcus sign (both in neutral and external rotation) for inferior translation

– Sulcus sign graded as 3+ that remains 2+ in external rotation is pathognomonic for multidirectional instability (MDI)

• Specific tests

– Jerk test (Fig. 9-2)

Figure 9-2 The jerk test for posterior instability. A, The arm is forward flexed and internally rotated. B, Posteriorly directed force subluxes the shoulder. Slow abduction of the arm results in a palpable jerk as the joint is reduced. This test has also been performed in reverse by moving the arm from an abducted position forward.

– Kim test (Fig. 9-3)

Figure 9-3 The Kim test for the detection of posteroinferior labral lesions is performed by applying axial compression to the 90-degree abducted arm (A), which is then elevated and forward flexed in a diagonal direction (B), resulting in pain and a possible clunk.

– Circumduction test

– Active compression or O’Brien test

Radiographs

• Plain radiographs including an axillary view, anteroposterior view, and scapular-Y view

– Reverse Hill-Sachs lesions (Fig. 9-4) of the humeral head

Figure 9-4 A reverse (anterior) Hill-Sachs lesion as demonstrated on an axillary radiograph.

Lesser tuberosity fracture

– Glenoid pathology (retroversion, rim fractures, and hypoplasia)

Additional West Point axillary view can be useful

– Bony humeral avulsion of the glenohumeral ligaments (HAGL)

• Magnetic resonance arthrography (MRA)

– Labrum (Fig. 9-5)

Figure 9-5 Axial magnetic resonance scan through the glenohumeral joint obtained with the intra-articular administration of contrast material demonstrating a capacious posterior capsule.

Kim classification is used to specifically describe posterior labral tear morphology ¹²

Type I, incomplete detachment

Type II (the “Kim lesion”), a concealed complete detachment

Type III, chondrolabral erosion

Type IV, flap tear of the posteroinferior labrum

– Capsule, biceps tendon, subscapularis integrity

– Soft tissue reverse HAGL lesion

– Posterior labrum periosteal sleeve avulsion (POLPSA)

• Dynamic MRA

– Demonstrate labral peel-back in the abduction and external rotation (ABER) position, consistent with posterosuperior labral tear (or type VIII superior labral anterior-posterior [SLAP] tear)¹³

• Computed tomography (CT)

– Glenoid version, locked posterior dislocation (Fig. 9-6)

Figure 9-6 Axial computed tomographic scan demonstrating a locked posterior dislocation with large reverse Hill-Sachs lesion and destruction of a significant portion of the articular surface.

Treatment

Many patients with RPS can be managed successfully without surgery. Numerous authors have proposed a period of no less than 6 months of physical therapy before consideration of surgical treatment.5,14 Effective rehabilitation includes avoidance of aggravating activities, restoration of a full range of motion, and shoulder strengthening. Strengthening of the rotator cuff, posterior deltoid, and periscapular musculature is critical. The premise of such directed physical therapy is to enable the dynamic muscular stabilizers to offset the deficient static capsulolabral restraints. Nearly 70% of patients improve after an appropriate rehabilitation protocol. The recurrent subluxation, however, is generally not eliminated, but the functional disability is diminished enough that it does not prevent activities.¹⁵ If the disability fails to improve with an extended 6-month period of directed rehabilitation, or in select cases of posterior instability resulting from a macrotraumatic event, surgical intervention should be considered.

Indications and Contraindications

Patients failing extensive physical therapy protocols should receive surgical consideration. Interval plication and suture capsulorrhaphy techniques have improved arthroscopic results, making them comparable to open procedures.10,16–18 Advantages of arthroscopic techniques over traditional open techniques include less disruption of normal shoulder anatomy; better visualization of intra-articular landmarks; the ability to perform concomitant SLAP repairs, capsular tear or rent repairs, and anterior and posterior stabilization procedures; and complete visualization of both the intra-articular and subacromial spaces. The surgeon’s transition from open to arthroscopic techniques can be difficult. Arthroscopic techniques require the surgeon to be familiar with anchor placement, suture management, and arthroscopic knot tying. A thorough understanding of arthroscopic anatomy is vital to the success of arthroscopic stabilization procedures. Open techniques require larger incisions, a deltoid-splitting approach, and either splitting the bipennate infraspinatus muscle or developing the interval between the infraspinatus and the teres minor. On the other hand, open techniques allow complete visualization of the posterior capsule and offer the opportunity to perform a reliable capsular shift and/or posterior labral repair.

Indications for arthroscopic posterior stabilizations include patients with continued disabling isolated RPS after a rehabilitation program, RPS with a posterior labral tear, MDI with a primary posterior component, and voluntary positional posterior instability. Relative indications include patients with an antecedent macrotraumatic injury. Contraindications include patients not having completed a reasonable rehabilitation program, a surgeon preference for traditional open techniques, a large engaging reverse Hill-Sachs lesion requiring subscapularis transfer or an osteochondral allograft, a large reverse bony Bankart lesion, patients with muscular voluntary instability and underlying psychogenic disorders, and patients unable or unwilling to comply with postoperative limitations. Relative contraindications may include chronic instability resulting in compromised capsulolabral tissue, and patients who have undergone previous open surgery. Because successful results have been achieved with arthroscopic treatment of posterior labral tears in contact athletes,10,19 arthroscopic reconstruction is not contraindicated in this population.⁹ As arthroscopic techniques continue to evolve, the surgical indications will likely broaden.

Only gold members can continue reading. Log In or Register to continue