Introduction

Reducing the surgeons' cumulative radiation exposure and improving the positioning accuracy during orthopaedic surgeries are key issues in computer-assisted orthopaedic surgery. Over the past years, we have developed FRACAS, a computer-integrated system for assisting surgeons in closed long bone fracture reduction. The FRACAS system replaces uncorrelated static fluoroscopic images with a virtual reality display of three-dimensional bone models created from preoperative CT and tracked intraoperatively in real-time.

Two issues that require special attention are distal locking and surgeon training for system acceptance. Due to nail bending, distal locking requires automatic recognition of nail holes and an adjustable drill guide to ensure that the holes are drilled in the right position. Surgeon training devices are useful to familiarize surgeons with real-time 3D displays and multiple views, to understand optical tracking requirements, and to study ergonomic issues.

Materials and methods

We have developed two devices and related software for in-vitro experimentation and training for computer-aided closed medullary nailing: one is a fracture reduction simulator and the other is an adjustable drill guide for distal locking.

The simulator consists of two adjustable bone fragment holders mounted on a radio-lucent basis, whose positions are followed by an optical tracking device. Each bone fragment holder is a spring-loaded lockable spherical joint to which distal and proximal bone fragments are attached. The holder of the distal fragment also translates, simulating the action of the muscles on the bones. The device allows surgeons to practice bone alignment and distal nailing based on two and three-dimensional images. It allows us to perform ergonomy and accuracy experiments, and to determine the best position of the LED pins.

The adjustable drill guide is a radio-lucent, five-degree of freedom device for assisting the surgeon in drilling the holes for distal locking screws. The guide attaches to the nail's head like the proximal targeting fixture. The drill is tracked in real time, and its position with respect to the nail holes is determined by image processing and registration software. The axes of the nail holes are automatically identified in the fluoroscopic images, and registered to the bone model. The surgeon can then adjust the position and orientation of the drill guide until its axis and the axis of the nail are identical.

The surgeon practices aligning the nail holes extracted and the drill guide hole axes extracted from fluoroscopic images following their spatial view on the computer screen. The guide, whose position and orientation is tracked in real time, can also be used independently as a targeting device.

Results

Both devices have been integrated to the current FRACAS system. Preliminary experiments show improvement in the acceptance of the computer-aided system and allow for accuracy evaluation of image-based methods.

Reference

``FRACAS: A System for Computer-Aided Image-Guided Long Bone Fracture Surgery'' L. Joskowicz, C. Milgrom, A. Simkin, L. Tockus, Z. Yaniv, Journal of Computer-Aided Surgery}, Vol. 3(6), May 1999, pp 271-288

Keywords: Computer-assisted orthopaedic surgery, closed medullary nailing, fracture reduction, distal locking, targeting device, training simulator.

Proc. 14th Int. Congress on Computer-Assisted Radiology and Surgery , CARS'2000, H.U. Lemke et. al. eds, Elsevier 2000.