Why Frozen Shoulder Develops
Frozen shoulder (adhesive capsulitis) occurs due to fibrotic inflammatory changes in the glenohumeral joint capsule, triggered by a combination of systemic metabolic disorders, shoulder immobilization, and neurological injury, though the precise etiology remains incompletely understood. 1, 2, 3
Primary Risk Factors
Age and Sex
- Peak incidence occurs between ages 40-65 years, with individuals under 40 rarely developing the condition. 1
- Women comprise approximately 70% of cases, though the mechanistic role of sex hormones in disease development remains unclear. 4
Metabolic and Endocrine Disorders
- Diabetes mellitus represents one of the strongest risk factors for adhesive capsulitis, with insulin resistance potentially contributing to capsular fibrosis through chronic low-grade inflammation. 2, 5
- Thyroid disorders (both hypothyroidism and hyperthyroidism) significantly increase risk, suggesting endocrine dysregulation plays a pathogenic role. 2, 1
- Patients with polyarticular hand osteoarthritis face elevated risk as part of generalized osteoarthritis patterns. 1
Post-Trauma and Immobilization
- Shoulder immobilization following any shoulder surgery or injury directly triggers frozen shoulder development, emphasizing the critical importance of early mobilization. 1
- Failure to initiate formal physical therapy within 6-8 weeks post-injury or post-surgery may result in permanent shoulder dysfunction. 1, 6
Neurological Injury
- Up to 67% of stroke patients with combined motor, sensory, and visuoperceptual deficits develop shoulder-hand-pain syndrome, which frequently progresses to adhesive capsulitis. 1, 7, 6
- Improper handling during rehabilitation—particularly aggressive overhead pulley exercises—significantly increases risk in hemiplegic patients. 1, 7, 6
- Inadequate protection of the hemiplegic limb increases trauma risk and subsequent capsulitis development. 7
Oncologic Associations
- Breast cancer treatment is identified as a significant risk factor, with oncology-related therapies (surgery, radiation, chemotherapy) associated with higher incidence. 6
Pathophysiologic Mechanisms
Capsular Changes
- The condition represents fibrosis of the glenohumeral joint capsule with chronic inflammatory response, primarily affecting the rotator interval and axillary recess. 3, 7
- Capsular thickening and contracture develop progressively, with the coracohumeral ligament showing characteristic thickening on imaging. 2, 8
Emerging Hypotheses
- Recent evidence suggests the GABAergic system may play a decisive role, potentially linking type 1 diabetes, autoimmune endocrine disorders, and frozen shoulder through shared pathophysiologic mechanisms. 5
- The combined presence of psycho-emotional stress factors and pathogenic immune challenges may represent primary causative factors. 5
Clinical Implications
Pattern of Motion Loss
- External (lateral) rotation is the most severely affected motion and correlates strongly with the onset of shoulder pain, serving as a key diagnostic feature. 7, 6
- Equal restriction of both active and passive range of motion in all planes distinguishes adhesive capsulitis from rotator cuff pathology. 7, 6
Natural History Reconsidered
- Traditional teaching suggested spontaneous resolution within 1-2 years without treatment, but recent evidence demonstrates persistent functional limitations if left untreated, challenging the "benign neglect" approach. 2
Critical Pitfalls to Avoid
- Do not delay physical therapy beyond 6-8 weeks post-injury or immobilization, as this window is critical for preventing permanent dysfunction. 1, 6
- Avoid aggressive overhead pulley exercises in at-risk populations (post-stroke, post-cancer treatment), as these worsen the condition rather than improve it. 1, 7, 6
- Recognize that multiple shoulder pathologies can coexist—rotator cuff tears, calcific tendinitis, and subacromial bursitis must be actively excluded through imaging and examination. 6