How can one differentiate calcific tendonitis of the shoulder from an avulsion fracture of the shoulder?

Differentiating Shoulder Calcific Tendonitis from Avulsion Fracture

Standard shoulder radiographs (AP views in internal and external rotation plus axillary or scapula-Y view) are the definitive initial imaging to distinguish between calcific tendonitis and avulsion fracture, with calcific deposits appearing as fluffy, cloud-like opacities within the tendon substance versus the sharp, corticated bone fragment with a donor site defect seen in avulsion fractures. 1

Imaging Approach

Initial Radiographic Evaluation

• Obtain a minimum 3-view shoulder radiograph series including AP views in internal and external rotation plus either axillary or scapula-Y view, as this is the preferred initial diagnostic modality for acute shoulder pain and can delineate most shoulder fractures and calcific deposits 1
• The axillary or scapula-Y views are vital because AP views alone can miss critical pathology 1

Key Radiographic Distinguishing Features

Calcific Tendonitis:

• Appears as calcium deposits within the rotator cuff tendons, most commonly the supraspinatus (66.7% of cases), followed by infraspinatus (42.8%) and subscapularis (21.1%) 2
• The calcification has a fluffy, cloud-like appearance without cortical margins 3
• Located within the tendon substance itself, typically near the greater tuberosity insertion 4
• No disruption of the underlying bone cortex or donor defect 3

Avulsion Fracture:

• Shows a corticated bone fragment separated from its origin (typically the greater tuberosity for rotator cuff avulsions) 1
• Clear donor site defect visible on the bone surface 1
• Sharp, well-defined margins with trabecular bone pattern visible within the fragment
• Associated soft tissue swelling and potential displacement 1

Clinical Context Matters

History and Presentation

• Calcific tendonitis typically occurs in the fifth and sixth decades among sedentary workers, with acute severe pain during the resorptive phase (lasting 3 weeks to 6 months) but may have a chronic formative phase lasting 1-6 years that is often asymptomatic 4
• Avulsion fractures occur acutely following trauma with immediate onset of pain and functional limitation 1

Physical Examination Findings

• Tenderness directly over the greater tuberosity generally differentiates calcific tendinitis from other conditions 5
• Pain in calcific tendonitis is typically not activity-dependent, whereas fracture pain worsens with movement and loading 5

Common Diagnostic Pitfall

The critical pitfall is that acute calcific tendinitis can mimic fracture of the greater tuberosity on initial radiographs, particularly in younger patients presenting after trauma 3. A 7-year-old boy presenting with acute painful shoulder after a fall had initial radiographs that mimicked a greater tuberosity fracture, but subsequent investigation confirmed calcific tendinitis with complete resolution 3.

Advanced Imaging When Radiographs Are Indeterminate

CT Without Contrast

• Use CT when radiographs are indeterminate for comprehensive fracture characterization, as it is advantageous in identifying subtle nondisplaced fractures and characterizing fracture morphology 1
• CT can affect clinical management in up to 41% of patients with proximal humeral fractures 1

MRI Without Contrast

• Consider MRI when radiographs are noncontributory and you need to evaluate for associated rotator cuff pathology, as 30% of calcific tendonitis patients have concurrent rotator cuff tears 2
• MRI allows better evaluation of coexisting pathology including osseous contusions, tendon infiltration by calcium deposits (present in 84.4% of cases), and rotator cuff integrity 4, 2