Evaluating long bone fractures in children: A biomechanical approach with illustrative cases

The following should be considered when evaluating a child with a long bone fracture: What are the biodynamics of the injury event, the energies generated by the event, and how could certain factors of the injury environment contribute to the likelihood of injury? What injuries are expected, and what is the likelihood that the event generated the specific load required to cause each and all of the injuries? Did the energy of the event exceed the injury threshold, or was there a biological abnormality such as decreased bone density that resulted in a lowering of the actual threshold for injury? Is there evidence of bone weakness or disease? Is the fracture morphology consistent with the direction, magnitude, and rate of loading of the described mechanism? Is the fracture pattern unusual, and one that requires an extremely unusual loading condition, as is the case with a CML? What is the child's developmental capabilities and could the child have generated the necessary energy, independent of "outside" forces, to cause the observed injury? Does the fracture reflect a high-energy fracture? Did the event generate enough energy to cause a high-energy fracture? Or is the fracture a small cortical defect, or hairline crack, reflecting a smaller amount of energy required for propagation of the fracture type? What regions of the bone have been injured and what are the structural components that affect the ultimate pattern of fracture that is being observed? Were there structural factors that contributed to the likelihood of fracture? Mechanisms of injury generate specific forces called loads that have the potential to cause structural damage. If the mechanism results in forces that exceed the injury threshold of a long bone, then a fracture is generated. The fracture morphology is a direct reflection of the degree and direction of the forces and the ability of the tissue to resist those forces. Mechanisms that generate greater amounts of energy with greater magnitudes of force may result in a completed fracture with the fracture type depending on the resultant combination of forces and moments. The fracture may be angulated or displaced, again reflecting a greater magnitude of force that has propagated the fracture. Fracture patterns such as classic metaphyseal lesions reflect unusual types of loading forces. When fracture morphology seems inconsistent with the history, or reflects a high-energy fracture pattern, or an unusual type of loading, it is paramount to determine how and if the explained mechanism generated the necessary forces to create the observed injury. If an inconsistency exists, further investigation to evaluate for abusive trauma is warranted. When evaluating fractures in children, it is critical that the clinician determine if the injury and stated mechanism are consistent. Observations of the resultant damage (fracture, and other injuries if present) and historical details of the scenario provide necessary input for reconstruction from a biomechanical, physics-based consideration of the injury, and evaluation of injury plausibility. Approaching childhood injuries from a biomechanical point of view allows for a better understanding of the type and magnitude of forces to which a child is being subjected. This in turn helps to better define the level of risk involved and the means necessary to ensure the future safety of the child. The response and intervention must equal the injury risk that biomechanics helps clarify scientifically. If the trauma is minimized, underestimated, or misinterpreted, the intervention needed to protect the child may fall short.