Institute of Computer Science The Hebrew University of Jerusalem, Israel

Master of Science Thesis, 1997.

Fluoroscopy-based orthopaedic procedures crucially depend on the ability of the surgeon to mentally recreate the spatio-temporal intraoperative situation from uncorrelated, two-dimensional X-ray images. Significant skill, time, and frequent use of the flouroscope are required, leading to positioning errors and complications in a non-negligible number of cases, and to significant cumulative radiation exposure of the surgeon.

The work described in this thesis is part of an ongoing effort in developing a computer-integrated system for assisting surgeons in closed intramedulary nailing reduction of long bone fractures. The system will provide the surgeon a ``virtual reality'' view of the intraoperative situation: a realistic, three-dimensional image of the the bone fragments and surgical tools that is updated in real time when their position changes. The surgeon will manipulate the bone fragments and surgical tools, following the results on the screen monitor, until the desired geometric and spatial relations are achieved. Fluoroscopic images will only be necessary for validation and calibration.

This thesis describes a software prototype that supports modeling, visualization, and preoperative planning for each individual patient. The system builds 3D geometric models of the healthy and fractured bones from a sequence of 2D images obtained before surgery by Computerized Tomography (CT). Using the visualization module, the surgeon can interactively examine the bone models and identify the upper and lower bone fragments to be joined by the nail. The planning system allows the surgeon to determine the optimal length and diameter of the nail by interactively positioning a nail CAD model chosen from a catalog inside the healthy bone model. The bone fragment models will be used to visualize their relative position during surgery and match the fluorosopic images. While the system is targeted to closed intramedulary nailing, many of its components can be used for other orthopaedic procedures.

Keywords: CT modeling, preoperative planning, medical visualization, orthopaedics