Visualization and analysis of the deforming piglet femur and hip following experimentally induced avascular necrosis of the femoral head.

Childhood avascular necrosis (AVN) of the femoral head leads to its progressive deformation and compensatory changes of the adjacent acetabulum. To simulate this disease for laboratory study, we used an AVN model of the hip in a skeletally immature piglet. The 3-D visualization and analysis of this piglet's deforming femur and hip form the basis for this paper. In particular, the data for this analysis were generated via serial CT images of bilateral femurs and acetabula of a piglet at regular time intervals following experimental unilateral induction of femoral head AVN. The contralateral femur and acetabulum served as the control. We applied a shape analysis technique that effectively captured not only the temporal shape changes of the femurs and acetabula, but also their codependencies. The resulting computational framework not only confirmed the widely accepted deformational changes of the femoral head following AVN; it also revealed the underappreciated compensatory changes of the surrounding acetabulum. The 3-D visualization of these dynamically changing structures provided a visual understanding of the shape changes associated with the AVN and control models. By quantitatively mapping the deformation trajectory of these shapes over time, we created an objective tool for clinical decision making.