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Skeletal Manifestations of Pediatric Nonaccidental Injury
Prevalence, Epidemiology, and Definitions
Nonaccidental injury (NAI; child abuse) is a widespread social problem of special concern to pediatricians. It is present worldwide but has different manifestations in differing cultures with increased awareness in Western societies. The presentation varies from neglect, thermal injury, sexual abuse, bruising to physical neurocranial and skeletal injury. The true prevalence is hard to obtain because it frequently occurs behind closed doors, is unobserved, and confessions are rare. When abuse is suspected, legal issues of parental rights and family preservation may interfere with diagnosis. In the United States, about 1500 children die each year as a result of child abuse. Boys and girls are affected equally. Most cases occur before the age of 6 years with a predominance in premobile infants. Accidental injuries are rare in children younger than 1 year of age and occur occasionally only. Risk factors include prematurity, low birth weight, physical disability, and low socioeconomic level. The perpetrator is most commonly a family member.
Caffey first described the association of unexplained subdural hematomas and long-bone fractures in infants in 1946. In 1953, Silverman recognized that skeletal injuries were the result of repetitive nonaccidental trauma. In 1962, Kempe and colleagues presented radiographic skeletal manifestations of child abuse and introduced the term battered child syndrome, now referred to as nonaccidental injury. NAI means an injury that is not explained by a naturally occurring accidental event matching the explanation from the child's caregivers. It does not imply intent and is usually due to a caregiver becoming frustrated by the demands of a baby and reacting with unacceptable force. Sometimes this has fatal consequences, especially if there is associated head or abdominal injury. Early detection of skeletal injury may prevent further events cumulating in death due to head injury or permanent neurodisability.
Imaging
Radiologic imaging provides objective evidence in physical abuse. Established investigative protocols include routine skeletal survey, ophthalmic imaging, and neurocranial imaging.
Radiologists, pediatricians, and pathologists need to work in cooperation to optimize services.
The goals of imaging in NAI are as follows:
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Identify and diagnose (unsuspected) NAI in a clinical setting
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Provide objective forensic evidence to support or refute NAI
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Exclude true accidental trauma, predisposing medical disease or normal variants that mimic NAI
The fractures encountered in NAI are often highly specific. This chapter concentrates on the radiology of the bony injuries, but neurocranial and abdominal injuries may be associated features. The most important skeletal findings in child abuse are discussed, as well as differential diagnostic considerations and imaging strategies.
Fracture Pattern
NAI usually presents through the pediatrician when the history of injury does not explain the injury identified. A radiologist may identify typical fractures on imaging studies performed for other reasons (rib fractures on chest radiograph to exclude sepsis). The essential role of radiology is to prevent escalating injury that may ultimately be fatal or disabling.
An incorrect diagnosis of NAI may have significant consequences for the child and family. In each individual case, the presented history must be correlated with predisposing disorders, including prematurity, skeletal dysplasia, and metabolic disease to differentiate NAI from other diagnoses.
The characteristic distribution of fractures in NAI is well established. In infancy, skull fractures, rib fractures, and metaphyseal injuries predominate. In the mobile child, diaphyseal fractures of long bones are suspicious if the history does not match the injury. Specific skeletal injuries can be classified according to index of suspicion of NAI and the child's age.
There is a high level of suspicion in association with classic metaphyseal lesions (CMLs) and posterior rib fractures. Clavicular fractures in older children and subperiosteal new bone formation in infants are common findings with low specificity. Multiple fractures of different ages with an inconsistent history are highly suggestive of NAI, provided that bone disorder is excluded ( Table 39-1 ).
TABLE 39–1
Specificity of Radiologic Findings for Nonaccidental Injury in Premobile Infants
| High |
| Classic metaphyseal lesions (CML) |
| Fractures of different ages or mechanisms—spiral shaft fractures |
| Multiple or bilateral fractures |
| Rib fractures, especially posterior |
| Moderate Specificity |
| Epiphyseal separations |
| Vertebral body injury |
| Hand/foot fractures |
| Skull fractures (especially complex fractures) |
| Common but Low Specificity |
| Subperiosteal new bone formation |
| Clavicle, elbow, or long-bone shaft fractures in older children |
Pathology
Radiographic Evaluation
In all cases of suspected NAI in children younger than about 2 years of age, a skeletal survey is mandatory. A babygram (a single radiograph or several films of the entire infant) is unsatisfactory. The initial survey ( Table 39-2 ) includes anteroposterior and lateral views of the skull and spine, and anteroposterior views of the extremities, including hands and feet. Oblique views of the thorax increase the screening sensitivity for rib fractures. Additional views of any suspected abnormality must be obtained.
TABLE 39–2
Suggested Protocol for Skeletal Survey (Not a Babygram)
| Skull |
| Anteroposterior and lateral views (Towne's view for occipital injury) Skull radiographs should be taken even if a standard head CT has been performed. |
| Body |
| Frontal chest (including clavicles); whole chest, left and right oblique views of ribs Anteroposterior view of abdomen with pelvis and hips |
| Spine |
| Lateral whole spine—cervical and thoracolumbar (anteroposterior on chest or abdomen) |
| Limbs |
| Anteroposterior views of humeri and forearms Anteroposterior views of femurs, tibia-fibulas; dedicated views of both hands and both feet If joint-centered anteroposterior views of limbs are performed, ensure overlap has no midshaft omissions. |
| Supplemental Views |
| Lateral views of any suspected shaft fracture |
| Lateral coned views of the elbows/wrists/knees/ankles may show metaphyseal injuries in greater detail than anteroposterior views of the whole limbs. |
A follow-up chest radiograph should always be performed as a minimum (see later discussion on rib fractures). Specific follow-up views of areas selected by the radiologist may assist in dating fractures or eliminating normal variants. A full repeat skeletal survey performed 2 weeks later gives further information while balancing the forensic process against radiation burden.
Digital imaging systems are replacing film technology, although some systems do not provide high detail radiography. Kleinman and colleagues concluded that less attention is being paid to technical elements specific to digital imaging, which affects image quality. Regular quality control is needed to maintain imaging standard digital algorithms.
Skeletal scintigraphy is reserved for specific situations. It must be performed with high-resolution collimation and meticulous symmetric positioning of the limbs with imaging in comparable posture. The lower limbs should be imaged separately from the torso, especially if the bladder is full of radionuclide. It is sensitive in detecting rib and diaphyseal fractures but has a low sensitivity for skull fractures and metaphyseal fractures. Metaphyseal fractures may be obscured by the normal high uptake at the growth plate.
Scintigraphy may assist as follows:
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To resolve a doubtful fracture or variant on a radiograph
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To detect additional rib fractures before they are visible radiographically
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To demonstrate additional injuries in a child with a single fracture on a conventional imaging
Dating of Fractures
Precise dating is impossible; we may define only a likely time range for an injury. This is narrowest with a recent fracture and widest in a late remodeling injury.
The rate of healing depends on the child's age, being most rapid in the neonate.
Dating is best achieved by a radiologist experienced in reviewing healing on serial radiographs of children of different ages under fracture clinic review, or serial radiographs of rib fractures. A truthful clinical history may narrow the wide radiologic age range.
Radiologic Findings
Fractures of the Extremities
Classic Metaphyseal Lesion/Fracture
The incidence of CMLs ( Fig. 39-1A-D ) in NAI in infants is variously reported from 11% to 28%. These fractures are often multiple and found in various stages of healing. CMLs are more common in the lower limbs than in the upper limbs, and less frequently at the proximal joints than distal. They are often bilateral and symmetric but may be isolated.
The CML was first described radiologically by Caffey in 1974. It is referred to as a corner or bucket-handle fracture and is a distinctive feature of NAI. Kleinman and colleagues reevaluated this in 1986 using histopathologic and radiographic studies confirming that it represents a transmetaphyseal disruption through the immature primary spongiosa. The corner fracture and bucket-handle fracture are the same pathology but may have different appearances according to the orientation of the incident X-ray beam and the size of the avulsed fragment. CMLs may be identifiable on only one of many views of a joint. Localized views of a joint give a better profile than a single whole limb view.
Periosteal reaction in healing CMLs is variable and depends on the extent of subperiosteal bleeding. CMLs may heal with or without periosteal reaction. This makes dating difficult.
The metaphyseal lesions in NAI must be distinguished from normal variants such as metaphyseal beaks and spurs. Similarly normal irregularity in the distal ulna or medial proximal tibial cortex may cause confusion.
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