Arthroscopic repair of posterior shoulder instability

Introduction

Posterior shoulder instability is relatively uncommon when compared with anterior instability with an incidence range from 2% to 10% of shoulder instability cases. History and physical examination findings have improved diagnostic accuracy for this problem; however, greater physician knowledge and education are still needed. Surgical treatment has progressed from open suture only procedures to precise and patient-specific arthroscopic knotless anatomic suture anchor repair. Further knowledge regarding risk factors for posterior shoulder instability and failure of its surgical treatment is still necessary.

History

Although posterior shoulder injuries range from traumatic to locked posterior shoulder instability, athletes most frequently have pathology secondary to repetitive microtrauma leading to recurrent posterior subluxation (RPS). RPS commonly occurs in overhead throwers, baseball hitters, golfers, tennis players, butterfly and freestyle swimmers, paddling sport athletes, weightlifters, rugby players, and football lineman, among others. The more common cause of RPS is repetitive microtrauma, typically resulting from posterior capsular attenuation and posterior labral tears. Regardless of the type of athlete, patients with RPS often have somewhat vague and ambiguous complaints of diffuse pain and shoulder fatigue without a distinct complaint of instability, making this diagnosis difficult.

Throwers have a different mechanism of posterior shoulder injury which includes an avulsion of the posterior capsulolabral complex (PCLC) or a labral flap tear. Multiple mechanisms leading to these injuries can occur in throwers, including deceleration and eccentric load events leading to repetitive microtrauma. Another mechanism occurs when patients initially have a tight posterior inferior capsule (GIRD: glenohumeral internal rotation deficient), which leads to repetitive microtrauma after ball release, and thus progressive tearing occurs. Another common pathology seen in throwers is a tear beginning at the posterior superior labrum (2b superior labral anterior-posterior [SLAP]) which progresses inferiorly, comparable with a tension band, leading to a split in the labrum ( Fig. 9.1 ). A more dynamic pathology involves an imbalance of a weak or contracted pectoralis major muscle, which allows the latissimus to pull the humeral head posteroinferiorly. Mechanical symptoms or pain during follow-through is the typical complaint in this population. Like other athletes, instability is not the predominant issue. In those with a dynamic muscle imbalance, pain is typically seen at or just before ball release. ^,

Despite being less common, traumatic injury does occur, typically from a direct blow to the anterior shoulder or indirect forces that couple shoulder flexion, internal rotation, and adduction. The classic teaching for the most common indirect causes is accidental electric shock and convulsive seizures, although these are relatively uncommon in the general population. Recurrent or locked posterior shoulder dislocations from macrotrauma are rare in the athletic population. Typically, secondary to incomplete radiographic studies and a failure to recognize posterior shoulder prominence and mechanical block to external rotation, locked posterior dislocation may be overlooked in up to 80% of situations, particularly in the emergency department. Concomitant pathologies are common with posterior shoulder instability and include reverse Hill-Sachs lesions, reverse bony Bankart lesions, capsular ligament avulsions, excessive humeral or glenoid retroversion, glenoid hypoplasia, or glenoid bone loss.

Signs and symptoms

To appropriately diagnose posterior shoulder 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 typically 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), more often than instability. Bernhardson et al. compared groups of anterior and posterior instability and found that those with posterior shoulder instability typically had no identifiable injury, with pain as the primary complaint.

Knowledge of the athlete’s sport, position, and training regimen is critical in deducing the pathogenesis and specific pathology associated with RPS. An inquiry should also be made regarding mechanical symptoms, specifically clicking, clunking, or crepitation with motion. Often this crepitus can be reproduced during examination and is caused by discrete posterior capsulolabral pathology .