Non-Accidental Injury

Non-Accidental Injury (NAI) is physical abuse of a child, often by a caregiver.

• Epidemiology:
  • Peak age: under 2 years (especially under 1 year).
  • Boys slightly more affected.
  • Mortality: 10-30% in severe cases (shaken baby syndrome).
• Risk Factors:
  • Young, single parents.
  • Substance abuse, mental health issues.
  • Previous history of NAI in family.
  • Colicky or difficult child.
  • Low socioeconomic status (although occurs in all groups).
• Importance for Orthopaedic Surgeons:
  • Fractures are the second most common manifestation of NAI (after bruising).
  • Early recognition can save lives.

Mechanisms of Injury in NAI

• Shaking: Causes subdural hematoma, retinal hemorrhages. In infants, the head is large and the neck muscles are weak.
• Gripping/Squeezing: Causes posterior rib fractures (thumbs on spine, fingers on ribs).
• Twisting/Pulling: Causes metaphyseal corner fractures (avulsion at the chondro-osseous junction).
• Direct Blows: Long bone shaft fractures, skull fractures.

Why Metaphyseal Corner Fractures are Specific

• The metaphysis is weaker than the shaft.
• Twisting or pulling forces cause avulsion at the periosteal-bone junction.
• This mechanism rarely occurs in accidental falls.

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A fracture is rarely the first abusive injury - it is often the one that finally reaches an orthopaedic surgeon. The topic notes that any bruise in a non-mobile infant is suspicious; this section develops why, and gives the two clinical rules that turn that instinct into a defensible referral.

The sentinel injury. A sentinel injury is a minor but unexplained injury - most often a bruise, but also an intra-oral injury or a frenulum tear - in a young, pre-mobile infant, noticed by a caregiver or clinician before a later, more serious abusive event. These are the missed early warnings: in a case-control study, a prior sentinel injury was reported in a substantial minority of infants with definite abuse but in none of the non-abused controls, the lesion was a bruise in the large majority, most occurred before three months of age, and a medical provider had often been aware of the injury at the time without acting on it. The lesson is that a "trivial" bruise in a very young infant is a chance to intervene before the fracture or the head injury - not a finding to dismiss.

"Those who don't cruise rarely bruise." Accidental bruising tracks motor development. Independently mobile (cruising/walking) toddlers bruise over bony prominences - shins, knees, forehead - from everyday falls. Bruising in an infant who cannot yet cruise has no innocent mechanical explanation and must be explained or referred. Bruises over soft, protected, non-bony sites (the trunk, ear, neck, cheeks, eyelids, genitalia) are the abusive pattern at any age.

The TEN-4-FACESp clinical decision rule operationalises this for bruising in children under four years and infants. It flags bruising as high-concern when it involves any of these regions or features:

Applied to bruising in young children the rule is highly sensitive and reasonably specific for abusive injury, which makes it a screening prompt to escalate - not a diagnosis. A positive TEN-4-FACESp bruise, like a sentinel injury, mandates the full safeguarding pathway and a skeletal survey; it does not on its own prove abuse, and a negative rule does not exclude it.

HIGH SPECIFICITY (When present, NAI is highly likely):

• Metaphyseal Corner Fractures (Bucket-Handle): Classic. Caused by twisting/pulling.
• Posterior Rib Fractures: Caused by squeezing (thumbs on back).
• Scapula Fractures: Very unusual in children (requires significant force).
• Spinous Process Fractures: Direct blow or hyperflexion.
• Sternum Fractures: Direct blow.

MODERATE SPECIFICITY:

• Multiple Fractures at Different Healing Stages: Indicates repeated trauma.
• Bilateral Fractures: Statistically unlikely from single accident.
• Complex Skull Fractures: Multiple fracture lines, depressed.

LOW SPECIFICITY (Common in accidental trauma):

• Clavicle Fractures: Common in birth and falls.
• Long Bone Shaft Fractures: Can be accidental or non-accidental.
• Linear Skull Fractures: Common in falls.
• Toddler's Fractures: Common accidental injury.

Why is my child being investigated? When a child has an injury that doctors cannot easily explain, they have a legal and ethical duty to make sure the child is safe. This does not mean they are accusing you of anything - it means they are being thorough.

What investigations will be done?

• X-rays of the whole body (skeletal survey) to check for other injuries.
• A scan of the brain if there is any concern.
• An eye examination to look for signs of bleeding.
• Blood tests to rule out medical conditions.

What happens next? A team of doctors, social workers, and sometimes police will review the findings. Their goal is to ensure your child is safe.

What are your rights? You have the right to legal representation. Cooperating with the investigation is in your child's best interest.

The whole reason a skeletal survey is repeated, and the reason "multiple fractures at different healing stages" is a moderate-specificity flag, is that healing fractures can be approximately aged on radiographs. The orthopaedic surgeon is repeatedly asked - in clinic, in MDT, and in court - "how old is this fracture?" The honest, defensible answer is a range, never a precise day. (The underlying biology of callus formation is developed in the fracture-healing topic; here the focus is the radiological timeline and its medico-legal limits.)

The radiographic features of healing appear in a predictable sequence, but with wide and overlapping windows that depend on the bone, the fracture type and the child's age:

Key NAI-specific caveats:

• A fresh fracture has no periosteal reaction. The absence of healing means the injury is recent (broadly within the last week or so) - which is exactly why a negative initial survey is repeated at 10-14 days, when occult rib and metaphyseal fractures declare themselves with periosteal new bone.
• Classic metaphyseal lesions and rib fractures date poorly. Corner/bucket-handle metaphyseal fractures show little or no periosteal reaction and are notoriously hard to age; rib fractures are frequently invisible acutely and only become apparent as callus forms - reinforcing the value of the repeat survey and oblique rib views.
• Fractures of clearly different ages = repeated episodes. A non-healing fracture alongside a remodelling one cannot have occurred in a single event, which is the radiological basis of the "different healing stages" red flag.
• Bruises cannot be dated by colour. Despite courtroom tradition, the colour of a bruise does not reliably indicate its age; only the presence of yellow has any (weak) discriminating value, and multiple bruises of "different ages" by colour should not be presented as proof of repeated assault.
• Avoid over-precision in reports. State a defensible range and acknowledge the uncertainty; over-precise dating ("this fracture is exactly 12 days old") is a frequent and successful target for medico-legal challenge.

Clinical tip: Investigate mimics thoroughly, but a negative medical workup does not exclude abuse - and a confirmed medical condition (e.g. OI) does not exclude coexisting inflicted injury. Report if the clinical picture is suspicious.

Fracture Management in NAI Context:

• Priority is Child Safety: Fracture treatment is secondary to ensuring the child is protected.
• Conservative Treatment Preferred: Most NAI fractures can be treated non-operatively.

• Mandatory Reporting: Legal obligation. You are protected from liability if acting in good faith.
• Documentation: Your notes may be subpoenaed. Be factual, objective, and comprehensive.
• Avoid Speculation: Document what you observe, not your opinion on who caused it.
• Chain of Custody: If specimens or photographs are taken, maintain proper procedures.
• Expert Witness: You may be called as a witness. Be prepared to explain findings objectively.

• Recognition: Identify suspicious fracture patterns.
• Reporting: Notify appropriate authorities.
• Documentation: Meticulous records.
• Treatment: Treat fractures appropriately (usually conservative).
• Court Attendance: May be required as a factual or expert witness.
• Ongoing Monitoring: If child returns with new injuries, re-escalate.

Global epidemiology

• Child maltreatment is reported worldwide; physical abuse disproportionately affects infants, with the highest fracture and fatal-head-injury rates in the first year of life.
• Fractures are a common manifestation of physical abuse and are second only to bruising; up to a third of physically abused children have a fracture, and the proportion is highest in non-ambulant infants.
• Risk is increased by young/sole caregivers, parental substance misuse and mental illness, intimate-partner violence, social isolation and prematurity/disability of the child - but abuse occurs across all socioeconomic groups and no profile is diagnostic.

Side-by-side guideline comparison

Practice variation: high- vs limited-resource settings

• High-resource: dedicated child-protection paediatric teams, on-site paediatric radiology, ophthalmology and forensic input, statutory multi-agency pathways.
• Limited-resource: skeletal survey may be substituted by targeted/limited radiography; ophthalmology and CT/MRI may be unavailable; reporting frameworks and social-care infrastructure vary widely. The clinical threshold for suspicion and the duty to protect the child remain the same regardless of available investigations.
• Reporting is mandatory by law in many countries (e.g. across the US, Australia, parts of Europe and Asia) and professionally expected elsewhere; clinicians must know the local pathway, but the duty to act on reasonable suspicion is universal.

• Vitamin D deficiency as a cause of fractures: A recurring courtroom argument. Subclinical vitamin D insufficiency is common and does not, by itself, produce the fracture patterns of abuse; radiographic rickets is required before metabolic bone disease can plausibly explain fractures. This remains a contested medico-legal area.
• "Temporary brittle bone disease": A proposed entity used in some defences to explain multiple infant fractures. It is not accepted as a validated diagnosis in mainstream paediatric and radiological practice and lacks a reproducible evidence base.
• The biomechanics of abusive head trauma: The relative contribution of shaking versus impact, and the specificity of the "triad" (subdural haemorrhage, retinal haemorrhage, encephalopathy), remain debated. Current consensus is that the triad raises strong suspicion but is interpreted alongside the whole clinical and radiological picture rather than as standalone proof.
• Dating of fractures and bruises: Radiological fracture dating is broad (ranges, not precise days) and bruise colour does not reliably date injury; over-precise dating in reports is a frequent source of challenge.
• Whole-skeleton imaging in older children: The yield of routine skeletal survey falls sharply after 2 years, so imaging in the 2-5 year group is selective and guideline-dependent rather than uniform.