May Be Caused by

 Common

Ankylosing spondylitis

Arthritis

Avascular necrosis

Fracture

Gout

Hill-Sachs defect

Infectious arthritis

Rheumatoid arthritis

Sickle cell disease

Steroid medication

 Uncommon

Erb palsy with disuse

Glenohumeral dysplasia

Hemophilia

Multicentric reticulohistiocytosis

Neuroarthropathy

Periarthrosis humeroscapularis

Pigmented villonodular synovitis

Rickets

Rotator cuff tear with atrophy and upward subluxation

Syringomyelia

Traumatic arteriovenous fistula

Tuberculosis