What is frozen shoulder, also known as adhesive capsulitis, in individuals over 40 years old with underlying medical conditions such as diabetes, hypothyroidism, and Parkinson's disease?

What is Frozen Shoulder (Adhesive Capsulitis)?

Frozen shoulder is a shoulder condition characterized by equal restriction in both active and passive range of motion in all planes, with external rotation being the most severely affected movement, distinguishing it from rotator cuff pathology where passive motion remains preserved. 1

Core Defining Features

The diagnosis rests on three cardinal characteristics that differentiate frozen shoulder from other shoulder pathologies:

• Equal restriction of active and passive motion in all planes, which is the hallmark finding that separates this from rotator cuff tears 1
• No focal weakness on resistance testing, unlike rotator cuff pathology which demonstrates specific weakness patterns 1
• Absence of swelling or muscle atrophy on physical examination 1

Range of Motion Pattern

Frozen shoulder follows a characteristic "capsular pattern" of motion loss:

• External rotation is the most severely restricted and relates most strongly to the onset of shoulder pain 1, 2
• Abduction is severely limited, particularly in the frozen stage 1, 2
• Internal rotation is the least affected of the three movements 1

This creates the classic hierarchy: external rotation > abduction > internal rotation in terms of restriction severity 1

Anatomical Structures Involved

The pathology primarily affects specific anatomical regions:

• The rotator interval and axillary recess are the primary sites of capsular thickening and contracture 1, 2
• Approximately one-third of cases show associated shoulder tissue injury including effusion, tendinopathy, or rotator cuff tears 1, 2

Clinical Stages and Natural History

Frozen shoulder traditionally progresses through three phases 3, 4:

• Freezing phase: Progressive pain and stiffness develop
• Frozen phase: Pain may plateau while stiffness remains maximal
• Thawing phase: Gradual improvement occurs

However, recent evidence challenges the older belief that this is entirely self-limiting. Many patients experience prolonged symptoms and incomplete recovery if left untreated, with the condition typically persisting 2-3 years, though pain and limited motion may extend beyond this timeframe 4, 5

High-Risk Populations

Certain groups have substantially elevated risk:

• Diabetes mellitus patients have increased prevalence 6, 7
• Hypothyroidism patients show higher incidence 7
• Parkinson's disease patients are at elevated risk (as noted in the expanded question context)
• Post-stroke patients have up to 72% incidence of shoulder pain in the first year, with up to 67% developing shoulder-hand-pain syndrome when combined motor, sensory, and visuoperceptual deficits are present 1, 2
• Breast cancer patients post-axillary dissection have prevalence rates ranging from 1.5-50% 8

Critical Diagnostic Pitfall to Avoid

Do not confuse frozen shoulder with rotator cuff pathology. The key differentiator is that rotator cuff tears demonstrate focal weakness with specific resistance testing and may preserve passive motion, whereas frozen shoulder shows equal restriction in both active and passive motion without focal weakness 1. Additionally, degenerative joint disease, crystal arthropathies, and septic arthritis can mimic the presentation and must be excluded 2.

Imaging Considerations

• Diagnosis is primarily clinical based on history and examination findings 5, 7
• Radiography serves as basic diagnostics to exclude common differential diagnoses such as osteoarthritis or calcific tendinitis 4
• Coracohumeral ligament thickening on MRI yields high specificity when imaging is performed 7
• Imaging is reserved for exclusion of alternative pathology rather than confirming frozen shoulder 5