Posterior Instability of the Shoulder

Abstract

Posterior shoulder instability is representing less than 5% of all shoulder dislocations. The clinical presentation is not as clear as anterior instability, it can manifest in many forms, and pain is the most common complaint. Recent progress in the understanding of posterior instability has helped to more clearly define the possible treatment.

Traumatic posterior dislocations must be clearly differentiated from posterior subluxations (or recurrent posterior instability) because the anatomical lesions and therapeutic options of the two differ markedly.

Although they may seem complicated, these classifications are essential because they determine whether surgical treatment is needed. Anatomical posterior lesions may present as isolated labral lesions or be associated with true avulsion of the posterior capsular periosteum (reverse/posterior Bankart lesions), capsular laxity which is frequently posteroinferior, bone lesions such as posterior glenoid fractures or defects, or an anterior humeral head impression defect (McLaughlin lesion).

Kim et al. showed and classified different types of labral lesions in patients with posterior instability of the shoulder. The loss of chondrolabral containment is due to cumulative microtraumas on the posterior glenoid labrum by a mechanism of “rim loading.” The posterior labrum loses its normal height and becomes flat, with progressive retroversion of the chondrolabral glenoid. The “Kim lesion” corresponds to a superficial tear between the posterior labrum and the glenoid cartilage, without complete detachment of the labrum. Palpation of the lesion identifies fluctuation of the posterior labrum and reveals a loose attachment of the deep portion of this structure. The triad of indications for a Kim lesion includes a marginal crack or erosion, chondrolabral retroversion, and incomplete unidentified avulsion.

A full medical history and physical examination associated with specific imaging tests are necessary to determine the exact pathogenesis and the appropriate treatment options in these cases. An examination should include not only laxity tests but also specific instability tests of the shoulder. Pain is a typical primary complaint of posterior shoulder instability. Two sensitive and specific physical tests are the “Jerk Test” and “Kim Test,” which are based on provoking pain by compression of the labral lesion. The Kim Test is more sensitive for inferior labral lesions, while the Jerk Test is more sensitive for posterior labral lesions. A radiographic examination includes standard X-rays and an MRA or CT arthrography which improves visualization of labral lesions. Lesions of the posterior labrum may be classified using the classification by Kim et al. Posterior labral lesions, to include reverse Bankart lesions, Kim lesions, and POLPSA lesions, are best defined with MR arthrography. The treatment of posterior instability may include osseous surgical procedures (glenoid osteotomy and bone block, rotational osteotomy of the proximal humerus, posterior bone block, bone graft of anterior humeral defects, arthroscopic or open surgical treatment, etc.) and isolated or associated capsuloligamentary procedures (posterior capsulolabral repair (reverse Bankart procedure), posterior capsulorrhaphy alone or associated with bicipital tendon transfer (Boyd), or posterior capsular plicature (posterior Putti-Platt procedure)). More recently, advances in arthroscopic techniques have provided better understanding of the pathogenic mechanisms of these lesions and allowed the development of diverse capsulolabral repair techniques.