TECHNICAL POINTS OF COMPUTER ASSISTED INTRAMEDULLARY NAILING

Abstract

Introduction: Computer assisted Orthopaedic surgery (CAOS) has a lot to offer in orthopaedic trauma surgery. Based on real time fluoroscopic images CAOS can optimise the treatment of bone fractures while importantly reducing radiation exposure to both surgeon and patient. We describe our early experience with the use of the Brain LAB Vector Vision trauma software for the treatment of femoral shaft fractures with intramedullary nailing and distal cross bolting.

Materials and Method: At the beginning of the procedure two minimally invasive reference arrays are attached to the proximal and distal femur. Seven fluoroscopic images are acquired and automatically transferred to the navigation unit. These images are used to identify the shaft axis of both fragments, the neck axis and the posterior condylar axis to control alignment and rotation. Segmentation of the distal fragment is also performed to facilitate real time movement of the fragments during reduction. Two more fluoroscopic images are acquired once the nail is inserted to plan and navigate the interlocking screws. The software displays a real-time position of the drill guide during screw navigation. AO titanium femoral nails were used in all cases.

Results: Like all new introductions of CAOS technology there are problems to solve and tips that improve the technique. Specifically, proximal pin fixation needs to be rigid and is best put in to the greater trochanter to prevent obstruction of the nail. Real time fracture reduction has been easily achieved. Distal cross bolting requires at the present stage a further two fluoroscopic images when the nail is inserted. Navigation of the drill bit is accurate, but care needs to be taken because of the potential motion of the tip of the drill bit. As the software is generic any manufacturer’s nail can be inserted. There may be some advantage, however, in viewing a virtual nail insertion based on stored data in the software.

Conclusion: Acquiring good images and positioning of the navigation unit are key factors in successfully treating a femoral nail with the aid of CAOS. Already significant time savings in radiation exposure have been achieved in the early cases and this is expected to improve with more experience.