On skeletal survey imaging, which radiological finding is most specific for non-accidental injury (NAI) in a 6-month-old infant?

Explanation

## Non-Accidental Injury (NAI) — Skeletal Imaging Findings **Key Point:** **Metaphyseal corner (bucket-handle) fractures** are the most specific radiological sign of NAI in infants and young children. These fractures result from violent shaking or twisting of the extremities and are virtually pathognomonic for abuse. ### Metaphyseal Corner Fractures — Mechanism & Specificity **High-Yield:** Metaphyseal corner fractures occur at the **junction of the metaphysis and epiphysis** when the limb is forcefully pulled, twisted, or shaken. The infant's weak metaphyseal bone is avulsed by the periosteal attachment, leaving a characteristic small triangular or crescent-shaped fragment. | Feature | Detail | |---------|--------| | **Location** | Metaphyseal margins of long bones (femur, tibia, humerus) | | **Appearance** | Small triangular or crescent-shaped fragments ("corner" or "bucket-handle") | | **Specificity for NAI** | ~95% (almost never accidental) | | **Age group** | <2 years (peak 6–18 months) | | **Mechanism** | Violent shaking, pulling, or twisting of limbs | | **Associated findings** | Rib fractures (especially posterior), subdural hematoma, retinal hemorrhages | ### Skeletal Findings in NAI — Spectrum of Specificity | Finding | Specificity for NAI | Notes | |---------|-------------------|-------| | **Metaphyseal corner fractures** | ~95% (Highest) | Pathognomonic; virtually never accidental | | **Posterior rib fractures** | ~80–90% | Caused by squeezing; accidental rib fractures are rare in infants | | **Subdural hematoma** | Moderate | Often accompanies NAI but can occur in accidental trauma | | **Retinal hemorrhages** | Moderate | Seen in abusive head trauma; rare in accidental falls | | **Subperiosteal new bone** | Low | Can occur with metabolic disease, infection, or healing from any trauma | | **Generalized osteopenia** | Very low | Suggests metabolic disease (rickets, osteogenesis imperfecta), not NAI | | **Linear skull fractures** | Very low | Common in accidental falls; crossing suture lines does NOT indicate abuse | **Clinical Pearl:** When a metaphyseal corner fracture is identified in an infant, **child protective services must be notified immediately**. This finding, especially when multiple fractures of different ages are present, is a red flag for systematic abuse. **Mnemonic: FRACTURES in NAI** — **F**emur metaphyseal, **R**ib (posterior), **A**ccidental story doesn't fit, **C**orner/bucket-handle, **T**wisting injury, **U**nder 2 years, **R**etinal hemorrhages, **E**pidural/subdural, **S**ubdural hematoma. ### Why Other Findings Are Less Specific - **Linear skull fractures:** Common in accidental falls, especially crossing suture lines. Depressed or complex fractures are more concerning. - **Subperiosteal new bone formation:** Can be seen in healing from any trauma (accidental or non-accidental), metabolic bone disease (rickets), or infection (syphilis, osteomyelitis). - **Generalized osteopenia:** Suggests metabolic disease (vitamin D deficiency rickets, osteogenesis imperfecta, hypophosphatasia), not abuse. [cite:Caffey's Pediatric Diagnostic Imaging 13e Ch 2; Radiology 2009 Vol 251 No 1]