A 4-year-old child presents with elbow swelling after a fall on an outstretched hand. Lateral elbow radiograph shows elevation of both the anterior and posterior fat pads, but no obvious fracture line is seen. The most appropriate interpretation is:

• A Occult supracondylar fracture until proven otherwise ✓
• B Normal study, no further imaging needed
• C Radial head subluxation
• D Olecranon bursitis

Explanation

Elevation of the anterior fat pad producing the sail sign, together with a visible posterior fat pad, indicates hemarthrosis distending the joint capsule. In children this finding is highly predictive of an occult supracondylar fracture of the distal humerus even when no fracture line is visible, so the elbow should be immobilised and treated as a fracture. Radial head subluxation (nursemaid's elbow) does not produce a joint effusion, and olecranon bursitis causes superficial soft tissue swelling without intra-articular fat pad displacement.

Reference: Grainger and Allison's Diagnostic Radiology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.