Shoulder Instability (Posterior)

Posterior shoulder instability accounts for up to 24% of all young and active patients who are surgically treated for shoulder instability. Clinical symptoms of posterior shoulder instability show a wide spectrum which ranges from reported traumatic posterior dislocation to recurrent painful subluxations or just pain or discomfort during movement without subjectively perceived instability. The ABC classification distinguishes three groups of posterior shoulder instability based on the nature of pathology (first time, dynamic or static) and two different subtypes based on the pathomechanical principle. Different clinical tests are at surgeon’s disposal, including the Beighton Score for hyperlaxity, the scapula assistance test for pathological muscle patterning, or the Jerk and Kim test for structural damage. If a structural lesion is present, a magnetic resonance imaging presents the gold standard to localize and quantify the deficiency. Nonoperative treatment should be the first option for patients with first-time posterior subluxation or dislocation (A1), functional dynamic posterior shoulder instability (B1), and constitutional static posterior shoulder instability (C1), while operation becomes necessary when an important structural lesion is present.