Causes / typical injury mechanism: The cause of frozen shoulder is unknown, but it has been associated with diseases such as diabetes mellitus type 1 and thyroid disease. It can follow traumatic injury to the joint, immobilization of the joint, or surgical intervention; however, the primary mechanism is idiopathic.

Classic history and presentation: Adhesive capsulitis typically follows a course of 3 phases. First (2-9 months), there is an insidious onset of pain that eventually becomes severe and disabling. The pain tends to be worse at night and stiffness gradually onsets. Second (4-12 months) is the contracture phase, which is characterized by stiffness and progressive loss of motion that interferes with activities of daily living. Pain typically improves in this phase. Third (5-24 months) is the recovery or "thawing" phase in which the symptoms gradually alleviate and there is an improvement in range of motion (ROM).

Prevalence:

• Age – Primarily affects patients in their 50s and 60s.
• Sex / gender – 70% of patients are women.

Risk factors:

• Type 1 diabetes
• Thyroid disorder
• Prolonged immobilization
• Parkinson disease
• Previous episode of adhesive capsulitis

Pathophysiology: The initial cause is unknown, but the pathophysiology involves an inflammatory response in the glenohumeral joint that results in fibroblast proliferation leading to increased collagen (type III) being laid down. This leads to fibrosis and thickening of the joint capsule and limited motion.

Grade / classification system:  Adhesive capsulitis can be classified as primary, which is idiopathic, and secondary, which is onset due to trauma or immobilization.