Video-navigated targeting unit (ViNTU) for interlocking of intramedullary nails-experimental study on a new technique

Abstract

Subject: Intramedullary nails are widespread in trauma care. More and more they are applied also for limblengthening and deformity correction of femur and tibia. The amount of time and radiation for interlocking of intramedullary nails is strongly correlated to the surgeons skills. Excessive amount of X-ray acquisitions may occur; one study lists as many as 48 to successfully complete the procedure. Multiple approaches for low radiation or radiation-free interlocking have been attempted. In this work, a novel low cost radiation-free drilling guide is designed to assist surgeons in completing the distal interlocking procedure with less X-ray acquisitions. Methods: An augmented reality fluoroscope that coregisters optical and X-ray images (Cam-C) was invented in our clinic. As an additional tool to this technique we designed a dill sleve (ViNTU) (Fig. 1) which can be navigated by the Cam-C. We exploit solely the optical images to detect the drilling guide in order to calculate the tip position in real-time by a complex algorithm. There is no need for the complex setup of the conventional navigation systems. The real-time navigation is displayed on the monitor as a lay-over to a single conventional X-ray shot so that the tip and the direction of the drill can be targeted visually. In a pilot study we tested the precision of the method in over 200 random poses. In the final lab study we measured duration and success of the drilling procedures (DP) with 6 test persons (2 students, 2 residents and 2 seniors) on covered dry bone phantoms. Results: The preliminary study showed a mean tip-estimation error of 1.72 +/- 0.7 mm. In the final study the success rate was 98.3 % (118 of 120 DP) with am mean duration of 60 s per DP (Fig. 2). Conclusion: In the present lab setup the combination of Cam-C and ViNTU provides accurate and fast DPs. Another study for video-assisted adjustment of the interlocking holes will be finished soon. The ViNTU could be manufactured inexpensively, the Cam-C needs our particular software and a c-arm with a digital output and some commercially available hardware (HD-camera, mirror, processor, monitor). (Figure Presented).