| Femoral head osteonecrosis is a debilitating orthopaedic condition resulting from loss of adequate blood flow to bone in the femoral head, with ischemic bone cell death progressing to fracture/collapse of the weakened necrotic bone and progressive hip joint degeneration. Current treatment methods are frequently insufficient to save the native femoral head, and poor long-term outcomes following total hip arthroplasty have prompted an ongoing search for new interventional therapies. The emu, a biped which undergoes human-like femoral head collapse, holds exciting promise as an animal model in which to investigate new treatments. Because of the novelty of using this species as a human disease model, detailed investigations of pertinent issues of homology, such as joint loading and rate of bone formation were undertaken. Additionally, specific challenges of creating segmental osteonecrotic lesions in the emu femoral head were also investigated.Interspecies homology issues were studied on both the microscopic and macroscopic size scales. Microscopic evaluation of rates of emu cancellous bone mineralization by fluorescent labeling suggested that emus have faster rates of bone formation than do established mammalian models of femoral head osteonecrosis. Macroscopic study of emu gait and whole-limb modeling allowed for calculation of emu hip contact forces. Forces in the emu hip were found to be slightly larger than human hip contact forces, but with a similar distribution over the femoral head.Specifically within the context of inducing segmental femoral head osteonecrosis in the emu, two main characteristics were explored: ability to control lesion size and ability to control lesion location. Lesion size was investigated using large-scale 2D and 3D quantitative histology analysis. Histology information was correlated with output from a thermal finite element model of liquid nitrogen cryoinsult, to facilitate predictions of necrotic lesion size following cryoinsult with specified input parameters. Structural finite element analysis and development of a specialty drill guide for intraoperative usage were used to study the effects of specifically located osteonecrotic lesions. Based on this body of work, the emu model of femoral head osteonecrosis is now much better posed as a vehicle for systematic studies of this important orthopaedic disorder. |
