On an anteroposterior pelvis radiograph used to assess developmental dysplasia of the hip, the angle formed between Hilgenreiner's line and a line along the acetabular roof is measured. Beyond infancy, a value consistently greater than how many degrees indicates acetabular dysplasia?

• A 10 degrees
• B 15 degrees
• C 20 degrees
• D 25 degrees ✓

Explanation

The acetabular index measures the slope of the acetabular roof against Hilgenreiner's line. In a normal newborn it may approach 30 degrees and decreases steadily with growth; after infancy a value above about 25 degrees defines acetabular dysplasia and predicts persistence or redislocation. Values of 15 to 20 degrees are normal for older children. Serial measurement guides decisions about pelvic osteotomy when dysplasia persists after closed or open reduction.

Reference: Tachdjian's Pediatric Orthopaedics, 5th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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