EARLY DIAGNOSIS OF GROWTH DISORDERS USING MR IMAGING

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Specialized cartilaginous structures at the ends of bones, the epiphysis and growth plate (physis), are the site of normal bone growth in children. Limb deformity results from damage to this growth cartilage. Prompt treatment of epiphyseal and physeal injuries can prevent or minimize abnormal bone growth. Because damage to the growth cartilage is not directly detectable radiographically, growth disturbances are discovered only months after injury, when bony abnormalities develop. The hypothesis to be evaluated is that Magnetic Resonance (MR) allows earlier and more accurate evaluation of growth disorders by showing alterations in the composition and vascularity of the growth cartilage. A corollary is that the likelihood of growth disturbance can be predicted by analyzing the pattern of injury to the growth cartilage. First, MR characteristics of the normal anatomy and development of the cartilaginous epiphysis and physis (including signal characteristics, and measurements of T2 relaxation times) will be correlated with histochemistry. The cartilaginous abnormalities due to direct injury to the physis will be studied in two animal models to test the following hypothesis: a) In transverse fractures, extension of the fracture to the epiphyseal side of the physis is detectable by MR and greatly increases the likelihood of growth arrest; b) In vertical fractures, development of a transphyseal vascularity and disorganization of the cartilage results in growth arrest. Abnormalities due to indirect injury to the growth cartilage will be studied in an animal model of epiphyseal ischemia to determine whether abnormal blood flow in the vascular channels of the unossified epiphysis (detectable by contrast- enhanced MR) results in ischemic damage to the epiphyseal and physeal cartilage and eventually in abnormal ossification. A cohort study of children with physeal fractures will be performed to evaluate the role of MR imaging in predicting bony bridge formation based on the early evidence of damage to the physeal cartilage. The ultimate goals of this research are; a) to develop methods of early detection of damage to the growth cartilage which will allow earlier therapy and prevention of deformity, b) to gain a better understanding of skeletal growth disturbances by seeing the evolution of cartilaginous injury in vivo, and c) to validate models which may serve for future research on new therapies for growth arrest.