A 50-year-old man with a both-column acetabular fracture undergoes CT evaluation. Although the femoral head appears medially displaced with the fractured fragments, the articular surface of the fragments remains smoothly congruent with the head, and the ilium is separated from the weight bearing segment. This finding is termed:
- A Spur sign
- B Gull wing sign
- C Secondary congruence ✓
- D Marginal impaction
Correct answer: C. Secondary congruence
Explanation
In a both-column fracture all acetabular fragments separate from the intact ilium, and the head may drift medially with the fragments while the joint surface itself stays congruent. This state is called secondary congruence and, when maintained, can allow acceptable function even though the fracture looks severe. The spur sign refers to the bare iliac fragment seen on the obturator oblique view, and gull wing describes impaction of the medial dome in elderly patients.
Reference: Rockwood and Green's Fractures in Adults, 9th ed.
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