A Surface Modelling System for the Study of Scoliosis

The trunk deformity associated with scoliosis is considered by many patients and physicians as more important than the spinal deformity itself. For this reason it is important to access the three-dimensional characteristics of the surface deformity. A surface modelling system has been developed to study this surface deformity. This system is comprised of software modules running on an IBM RISC6000 engineering workstation. This system displays a realistic model of the trunk which can be rotated and viewed from any orientation. The surface modeller contains three major components; systems for determining the boundary of the trunk data, for modelling the trunk using triangles and for display and manipulation of trunk images. Triangles were chosen for their computational simplicity which minimizes the time to construct and move the 3-D image of the trunk. Boundary generation from discrete data points is ill-defined and subjective. Any surface model of the trunk requires the boundary to be defined. Otherwise, triangles would be placed in regions which are not part of the trunk surface. A boundary determination routine has been developed which provides a best estimate of the trunk boundary and then permits the user to interactively eliminate unwanted artifacts. The surface modelling routine uses a modified form of McLain’s algorithm to define the triangles which constitute the surface model. This algorithm was modified to greatly increase its speed and a novel method is used to eliminate triangles which fall outside the boundary. The display provides a realistic three dimensional image of the trunk which appears illuminated from ambient light and spot light sources. Multiple views of the trunk or different trunk images can be shown for comparison purposes. This permits the clinician to compare changes which occur over time in trunk deformity. The software system can simultaneously show a model of the spine or photo image in conjunction with the trunk surface model. This helps relate surface deformity to the underlying spinal misalignment.