[Static posterior humeral subluxation without osteoarthritis (posterior shoulder instability type C1) : Where does it...

Type C1 posterior shoulder instability represents a pre-arthritic condition characterized by chronic, static posterior subluxation of the humeral head. Its multifactorial etiology includes increased glenoid retroversion, altered posterior acromial morphology, reduced humeral retrotorsion, abnormal scapulothoracic alignment, and muscular imbalances.

Clinically, the condition predominantly manifests as atraumatic shoulder pain, typically without overt instability symptoms. Diagnosis is based on a comprehensive clinical history, targeted physical examination, and the use of advanced imaging modalities, which allow reliable detection of posterior humeral head decentering, posterior glenoid rim deficiencies, reduced posterior acromial coverage, and labral hypertrophy.

Therapeutically, heterogeneous treatment approaches with very limited evidence exist, and no curative standard has been established. Conservative management focuses on neuromuscular control and strengthening of the rotator cuff. Surgical options include arthroscopic soft-tissue stabilization, cartilage repair procedures, and bony interventions such as osteotomies and bony augmentations of the insufficient posterior glenoid rim. However, current evidence predominantly demonstrates temporary symptom relief, without clear proof of sustained humeral head recentering.