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NDI InFocus February 2008

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• Computer-Assisted Therapy & NDI
• Aurora
• Orthopaedics

University of British Columbia uses Aurora Tracking Technology to Improve the Future of Intramedullary Nailing

For orthopaedic trauma cases in which a long bone such as a femur or tibia has a mid-bone fracture, it is typical to repair the bone through the insertion of a nail into the central medullary cavity of the bone shaft. This intramedullary implant is held in place with locking screws that go through the bone and into the implant at both the proximal and distal ends. However, the implant is often deformed in an unpredictable way during insertion, making it difficult to identify the positions and orientations of the distal locking holes. Fluoroscopy is typically used to visualize the locking holes so that a drill can be properly aligned to create paths through the bone for the screws, but this is not time efficient and exposes the surgical team to a significant amount of radiation. The accumulation of radiation exposure over the course of an orthopaedic surgeon’s career is a rising concern, and although several alternative locking techniques have been developed, the free-hand fluoroscopic approach remains the primary choice for surgeons.

The ability to continuously track the implant in real-time after insertion, and hence always being able to determine the positions and orientations of the distal locking holes to a high degree of accuracy, could largely eliminate the need for fluoroscopy during distal locking and significantly reduce the time required for this portion of the procedure. This can be accomplished with the Aurora^® system by inserting and temporarily affixing a 6DOF (six degrees of freedom) sensor into the hollow central canal of the implant, locating it as close as possible to the distal locking holes. Free-hand navigation of the drill is then easily accomplished by also tracking it in 6DOF with the Aurora system. After the distal locking screws are successfully put into place, the sensor can then be withdrawn from the implant before the patient’s incision is closed.

A research project to explore the possibility of this technique is currently underway at the University of British Columbia. The preliminary results have been very promising, and plans for a clinical trial are in progress. By tracking the locking holes internally and tracking the drill externally, the Aurora system may enable substantial improvements to the future of intramedullary nailing by allowing distal locking to be completed more quickly and without the use of fluoroscopy.

Reference:
Katie E Beadon, Jeff Stanley, Pierre Guy, Peter J O’Brien, Antony J Hodgson, “Electromagnetic tracking for navigation in computer-assisted distal locking for intramedullary nailing of the femur: a feasibility study”, 7th Annual Meeting of CAOS-International Proceedings, Heidelberg, Germany, June 20-23, 2007

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