Rickets
Rickets is a very common cause of osteopenia and may be recognized by its effect on the physis. The physis is frayed and the white line of the zone of provisional calcification is lost. In severe cases, the physis is cupped. With better nutrition, the zone of provisional calcification recovers, but physeal irregularity remains for a period of time.
Osteopenia is commonly present in premature children and other hospitalized children. Premature children can sustain multiple fractures including classic CMLs. Chronic renal or liver disease can also cause deficient bone mineral density and rickets. These patients may also sustain lesions that would ordinarily be suspicious of abuse. Injuries in these patients require a detailed clinical and social history to differentiate injuries sustained as a result of normal daily care from abuse.
Fractures in the hospital are not uncommon and difficulty arises when, soon after discharge, the patient returns to the emergency room with fractures, frequently located in the long bones. Chronically ill patients while in the hospital may not be handled as often as they are at home and accidents inevitably are common. However, chronically ill patients are also at increased risk for abuse [
39]. Dating the fracture as accurately as possible is very important. A fracture showing advanced callus is not likely to have been sustained at home if the patient has been home less than 2 weeks. However, soft tissue swelling seen at the site of a fracture with no evidence of subperiosteal new bone formation is more suspicious, depending on the time since discharge. In any case, a posteromedial rib fracture should not occur as it is associated with a very specific mechanism unlikely to be duplicated as a result of daily care.
When faced with a case with multiple fractures, an effort should be made to roughly date each fracture. An assiduous search should be made for those higher-specificity fractures such as CMLs. If posteromedial rib fractures are suspected but not conclusively seen on plain film, multidetector-row CT can be very helpful and diagnostic.
Osteogenesis Imperfecta
Osteogenesis imperfecta (OI) is a rare disease writ large when the differential diagnosis of child abuse is considered. The cardinal feature of OI is increased bone fragility and, as such, must be considered when considering an infant with multiple fractures.
OI is classified according to the classification of Sillence et al. [
59,
60], which for many years included only four types divided on both clinical and radiographic grounds. The Sillence classification describes a spectrum of disease rather than a strict system based on objective scientific identities. Type 1 is the most mild and patients have normal stature with little or no deformity. Type 2 is lethal in the perinatal period with beaded ribs, compressed deformed long bones, and minimal skull mineralization. Type 3 is of moderate severity with deformity generally present at birth. Type 4 is of mild to moderate severity with variable short stature and deformity. While with Types 2 and 3 the diagnosis is rarely in doubt, Types 1 and 4 engender considerable difficulties since both can be quite mild with little or no deformity present in infancy.
Types 1 to 4 are all caused by mutations in either the COL1A1 or COL1A2 gene, which encode for formation of the procollagen alpha-1 or alpha-2 chain. Two alpha-1 and one alpha-2 chains form the triple helix of collagen 1, which is the major contributor to the normal collagen matrix in bone.
Biochemical or mutation analysis is capable of identifying approximately 90% to 95% of patients with Types 1 to 4. The number is steadily increasing. However, recent descriptions of several new types of OI have changed the landscape.
Type 5 is typified by grossly hypertrophic callus about fractures and curious ossification of the interosseous membrane in the forearm [
19]. It is usually moderate in severity, although some variability can be observed. It is not a mutation in collagen 1 and is not identifiable by either mutation or biochemical testing aimed at collagen 1.
Type 6 is moderate in severity and indistinguishable from Type 4 clinically [
20]. It is not identifiable by mutation or collagen biochemical analysis. On microscopy of biopsied bone, it is indicated by a characteristic mineralization defect in bone.
Two new types classified as Types 7 and 8 are caused by abnormal posttranslational modification of the collagen molecule and are not identifiable by the traditional OI mutation or biochemical analysis. Both of these types manifest severe phenotypes with severe bone fragility. Metaphyseal changes and bulbous “popcorn” epiphyses, in which irregular dense calcifications are present, have been described [
5]. Given the severity of these types, they should not cause confusion when considered with respect of child abuse.
The complexity and variability present in OI make differentiation from abuse very challenging and both mutation and biochemical collagen analysis are frequently performed. Since the tests are only about 90% to 95% sensitive, the results can be unsatisfying and lead to confusion when trying to differentiate abuse from OI. However, several important points may be made.
While rib fractures can occur, it is generally in the more severe types. Fractures are usually lateral and are uncommon posteromedially. Posteromedial rib fractures even in a child with OI should be taken very seriously and, except in moderate to severe cases of OI, or in the face of severe osteopenia are highly suspicious for abuse because of the typical mechanism needed to produce those fractures. In severe OI, no mechanism is needed to explain a fracture, but in mild cases the mechanism of injury reigns supreme and must be considered.
CMLs are also highly suspicious. In epiphyseal cartilage, collagen 2 predominates. At the physeal level, collagen 1 is not present [
48] and is produced in the metaphyses [
56]. As such, the most fragile portion of the bones of a patient afflicted with OI is not the physes but the midshaft, where fractures are more frequent. CML-type injuries are extraordinarily rare in OI and are even more rare, if they occur at all, in children younger than 1 year [
4]. For a CML to occur, in the face of trauma, the physis and zone of provisional calcification need to have greater weakness when compared to the diaphyses and this is not usually the case in OI. There have been no reports in the literature describing an infant with OI sustaining a true CML.
Even beyond the limits of biochemical and mutational testing, it is clear there are certain types of fractures that remain highly specific for abuse and are extremely suspicious when encountered in an infant. It should be recognized OI is, in the end, a rare disease and it is rarer still to be one of the 5% to 10% of patients with negative biochemical and mutational testing. Therefore, while OI is not ruled out as the result of negative laboratory analysis, any fracture must be considered very carefully if the patient is an infant and an appropriate history is not provided.
OI has also been called brittle bone disease in the common parlance. A separate term, temporary brittle bone disease (TBBD), refers to a report by Colin Paterson, a Scottish physician, of infants with suspicious fractures who, by his account, were not abused. According to Paterson, TBBD affects children under 6 months of age who sustain fractures during the course of normal handling and care and later no longer fracture [
53,
54]. Paterson became a feature of many court cases in the United Kingdom and other countries in which the defense of TBBD was advanced, many times successfully. He emphasized the fractures occurred without a history of trauma or visible evidence of trauma, such as bruising, and without attendant internal injuries and the caregivers all denied wrongdoing [
46]. His theory has been severely criticized on each of his points [
1,
44]. Many abused children lack bruising, and while bruising is a helpful indicator of trauma, fractures occur frequently in the absence of bruising at any age. In addition, although associated injuries such as solid organ injury and retinal hemorrhages are common, it is by no means the rule. Finally, abusers tend to deny any culpability, some even after being found guilty in a court of law and in the face of overwhelming evidence. Because of his single-minded testimony at trial in support of this diagnosis, which included a lack of appropriate review of the records, among other inadequacies, Paterson was forbidden to act as an expert witness in the United Kingdom [
15]. Later, in 2004, he was “struck out,” meaning his medical licensure was lifted [
14]. In the United States, the TBBD defense cannot be used in many states’ courts of law and has been discredited.
Dr. Marvin Miller, an adherent of the TBBD concept, has advanced a possible theory that proposes a temporary state of increased bony fragility related to decreased fetal movement [
46,
47]. His theory has been criticized for methodologic errors, including an incomplete description of the injuries, a subjective history of decreased fetal movement, and a long delay between bone mineral density measurements and the time of trauma [
25]. In addition, his use of bone mineral density measurements is flawed in itself, as bone mineral density measurement is unreliable in young infants [
16,
44]. The most recent normative values do not include values for those younger than 5 years [
17,
44].
Recent Controversy
Most recently, Keller and Barnes [
28] questioned whether neonatal rickets, mild in nature and related to decreased vitamin D in breast-feeding mothers, can be blamed for fractures occurring early in life. This contention has been criticized by Slovis and Chapman [
61] on several counts, including a lack of observable findings of rickets that would include fraying and cupping of the physis on the published images from the original article. Indeed, one of the images of the distal ulna is claimed to show cupping consistent with rickets, but cupping of the distal ulna is a normal variant not associated with rickets as the sole finding [
18]. Keller and Barnes [
29] have since responded in kind, noting there are, by their account, other findings of rickets on the published images, among other assertions. At this point, the implication of these reports and replies is still unclear, but several points may be made. First, the theory of neonatal rickets as an explanation of CML-type injuries, if true, should only apply in those infants younger than 6 months since, over that age, most children have nutritional sources other than breast milk. Second, it should not apply in those infants younger than 6 months who are not breast fed. Third, a posteromedial rib fracture remains highly specific for abuse. Finally, each radiograph must be assiduously examined for even mild signs of rickets, which would include cupping and fraying of the metaphyses, a frayed bulbous appearance of the anterior ends of the ribs (rachitic rosary), and undermineralization of the bony structures. Note is made, in the majority, newborn bones are generally more sclerotic in appearance, with thick cortices and small medullary cavities, when compared to the bones of toddlers and children.
Miscellaneous Mimics
Mimics of abuse include conditions causing decreased sensation, including spinal dysraphism and congenital insensitivity to pain. In the former case, the diagnosis is usually known, but rarely an infant may present with a lower extremity fracture related to an undiagnosed diastematomyelia or other myelodysplasia. In congenital insensitivity to pain, multiple fractures may occur related to abnormal pain sensation. This rare syndrome can have both dominant and recessive inheritance, and injuries may mirror those seen in abuse [
42,
63]. A diligent neurologic examination and clinical history that uncovers the patient’s lack of pain sensation should provide adequate differentiation from abuse.
Congenital syphilis causes fragmentation of the metaphyses and subperiosteal new bone formation along the diaphyses in newborns [
22]. Both findings can simulate those seen in abuse. Clues to the correct diagnosis are the presence of Wimberger’s sign, seen as metaphyseal lucency in the medial subphyseal portion of the proximal tibia. It is usually bilateral and the defect spares the most recently formed few millimeters of the bone bark [
52] and so should not be misconstrued as a true CML. Other radiographic abnormalities include trophic irregular metaphyseal lucent bands and focal lytic lesions, which represent syphilitic gummas, clearly not present in abuse.
Scurvy [
7], vitamin A intoxication, Caffey’s disease, leukemia, and treatment with prostaglandin E all cause subperiosteal new bone formation [
65], both diffusely and focally, and, to that limited extent, can be confused with abuse, but in each case, the related signs, symptoms, and radiographic changes provide easy differentiation from abuse. However, both copper deficiency and Menke’s kinky hair syndrome, itself an abnormality of copper metabolism, can be difficult to differentiate from abuse. Radiographic findings include osteopenia, subperiosteal new bone formation, and metaphyseal spurs with fractures indistinguishable from CMLs [
21]. Patients may seize and usually manifest psychomotor retardation, although both may not be present in infancy. Wormian bones seen on skull radiographs are usually present and patients usually have sparse depigmented coarse hair [
2]. The neurologic features and sparseness of the hair are the main clues to the correct diagnosis. Copper deficiency was advanced by Paterson with reference to TBBD, but no direct clinical or biologic proof was ever submitted [
54]. Copper deficiency and Menke’s kinky hair syndrome can be confused with child abuse, but neither bears a sufficient resemblance to the unproven and oft-criticized diagnosis TBBD.