What are the causes of frozen shoulder?

Causes of Frozen Shoulder

Frozen shoulder develops from two main pathways: primary (idiopathic) causes with unknown etiology but strong metabolic associations, and secondary causes triggered by shoulder immobilization, trauma, or neurological injury. 1, 2, 3

Primary (Idiopathic) Frozen Shoulder

Metabolic and Endocrine Disorders:

• Diabetes mellitus is the strongest metabolic risk factor, with diabetic patients showing significantly increased susceptibility to frozen shoulder development 4, 5
• Hypothyroidism is closely linked to frozen shoulder development 5
• Dupuytren's syndrome is associated with frozen shoulder pathology 4
• Advanced glycation end-products accumulate in the shoulder synovium, particularly in diabetic patients 5

Emerging Pathophysiological Mechanisms:

• GABAergic system dysfunction may play a decisive role, potentially linking type 1 diabetes, autoimmune endocrine disorders, and frozen shoulder through shared pathophysiological mechanisms 4
• Psycho-emotional stress factors combined with pathogenic immune challenges may trigger primary frozen shoulder 4
• Low-grade chronic inflammation and insulin resistance contribute to disease development 4

Secondary Frozen Shoulder: Direct Causative Factors

Immobilization (Most Critical Modifiable Cause):

• Shoulder immobilization with arm slings and wraps directly promotes frozen shoulder development 2, 6
• Post-surgical immobilization, especially after breast cancer surgery with axillary dissection, causes frozen shoulder in 1.5-50% of cases 2, 6
• Prolonged immobilization from any cause creates the environment for capsular contracture 2

Neurological Injury:

• Stroke patients have up to 72% incidence of shoulder pain within the first year, with adhesive capsulitis being a common complication 1, 2, 6
• Patients with combined motor, sensory, and visuoperceptual deficits show shoulder-hand-pain syndrome rates as high as 67% 1, 2
• Shoulder subluxation and motor weakness are strong predictive factors for frozen shoulder in post-stroke patients 1
• Improper handling during rehabilitation, particularly overhead pulley exercises encouraging uncontrolled abduction, worsens shoulder complications 1, 6

Shoulder Trauma and Injury:

• Shoulder tissue injury including effusion, tendinopathy, or rotator cuff tears is found in approximately one-third of acute stroke patients and contributes to frozen shoulder 1
• Rotator cuff tears requiring extended periods of limited mobility trigger secondary frozen shoulder 2
• Direct shoulder trauma leading to prolonged immobilization initiates the pathological cascade 2

Post-Surgical Causes:

• Coronary artery bypass grafting (CABG) can lead to frozen shoulder, particularly in diabetic patients 7
• Head and neck cancer treatments cause cervical and shoulder range of motion restrictions 6
• Any surgery requiring shoulder immobilization increases risk 2

Underlying Pathophysiology

Inflammatory-Fibrotic Cascade:

• The pathological process begins with synovial inflammation followed by capsular fibrosis 8, 5
• Inflammatory cytokines, immune cells, and fibrotic growth factors accumulate in the synovium and joint capsule 5
• The immune cell landscape switches from macrophages to T cells as disease progresses 5
• Type-III collagen deposition occurs in affected tissues 5

Anatomical Structures Involved:

• The rotator interval and axillary recess are the primary anatomical structures involved in capsular thickening and contracture 1
• Imbalance between matrix metalloproteinases and tissue inhibitors of metalloproteases promotes fibrosis 5

Critical Risk Factor: Sedentary Lifestyle

• Today's sedentary lifestyle is associated with increased frozen shoulder prevalence 4

Common Pitfall to Avoid

Do not confuse frozen shoulder with rotator cuff pathology: Rotator cuff tears show focal weakness with specific resistance testing and preserved passive motion, whereas frozen shoulder demonstrates equal restriction in both active and passive motion with no focal weakness on resistance testing 1