Primary Causes of Frozen Shoulder (Adhesive Capsulitis)
Frozen shoulder develops through two primary pathways: idiopathic (primary) cases of unknown etiology, and secondary cases triggered by identifiable risk factors including diabetes mellitus, thyroid dysfunction, shoulder immobilization, and stroke. 1
Etiological Classification
Primary (Idiopathic) Frozen Shoulder
- The underlying cause remains unknown despite extensive investigation 1
- Represents spontaneous onset without clear precipitating factors 2
- Characterized by inflammatory cytokines and immune cell infiltration initially, progressing to fibrotic changes with type-III collagen deposition 2
Secondary Frozen Shoulder: Key Causative Factors
Metabolic and Endocrine Disorders
- Diabetes mellitus is the most common systemic association, with frozen shoulder frequently occurring in diabetic patients 3, 1
- Thyroid dysfunction (particularly hypothyroidism) demonstrates close pathophysiological links to frozen shoulder development 3, 2
- Advanced glycation end-products accumulate in the synovium of frozen shoulder patients, particularly those with diabetes 2
Immobilization-Related Causes
- Shoulder immobilization is a direct promoter of frozen shoulder development 4, 5
- Post-surgical immobilization, especially after breast cancer surgery with axillary dissection (prevalence 1.5-50%) 5
- Use of arm slings and wraps that restrict shoulder movement 4, 5
Neurological Conditions
- Stroke patients have up to 72% incidence of shoulder pain in the first year, with adhesive capsulitis being a common complication 6, 5
- Patients with combined motor, sensory, and visuoperceptual deficits show shoulder-hand-pain syndrome rates as high as 67% 6
Trauma and Injury
- Shoulder trauma leading to prolonged immobilization 6
- Rotator cuff tears requiring extended periods of limited mobility 6
Pathophysiological Mechanisms
Inflammatory Phase
- Initial pathology involves inflammatory cytokines and immune cell infiltration (macrophages transitioning to T cells) 2
- Activated fibroblasts regulate both inflammatory and fibrotic processes 2
Fibrotic Phase
- Progressive fibrosis with type-III collagen accumulation in joint capsule 2
- Imbalance between matrix metalloproteinases and tissue inhibitors of metalloproteases promotes fibrosis 2
Clinical Pitfall to Recognize
The GABAergic system may play a decisive role in frozen shoulder development, potentially linking type 1 diabetes, endocrinological autoimmune disorders, and frozen shoulder through shared pathophysiological mechanisms involving psycho-emotional stress and pathogenic immune challenges 7. This emerging hypothesis suggests frozen shoulder may represent a neuroimmune disorder rather than purely mechanical pathology.