Abstract
Computer aided orthopaedic surgery (CAOS) systems aim to improve surgeons’ consistency and outcomes by providing additional information and graphics, often displayed on one or more computer screens. Experience has shown that surgeons often feel uncomfortable looking away from the patient to focus on the computer screen, and multiple methods have attempted to address this (e.g. by using head mounted and semi-transparent displays). We present a new approach, with a small touch-screen wirelessly controlled from the main CAOS computer and micro-controlled electronics all mounted on the cutting instrument and placed along the surgeon’s line of sight from the instrument to the wound. In addition, the micro-controlled system improves the patient’s safety by controlling the cutting speed of the blade (or stopping it), based on the saw’s positioning deviations from the planned cuts. The (on board the saw) computer-user interface also transmits commands to the main computer, based on commands issued on the touch screen.
The “smart” navigated saw was built by integrating a microcontroller, optical trackers, a small 4x6cm viewable touch-screen, and a surgical oscillating saw. Bidirectional wireless communication was established between the saw and a Navigated Freehand Cutting (NFC) CAOS system allowing dynamic speed control of the blade, slowing it down for smaller errors in position/alignment (relative to planned cuts), and stopping it for bigger errors and/or risk of tissue damage. The sensitivity of the correction and width of the allowed error envelope were made adjustable to cater for the individual surgeon preferences. The touch-screen on the saw provided the surgeon with a visual aid for cutting without them having to look away while simultaneously providing control of the interface settings by touch. After electronic bench tests, two orthopaedic residents prepared eight synthetic distal femurs with the NFC system and the prototype saw to accept a commonly used TKR implant.
All parts were integrated into a usable stand-alone device, with no software, hardware, or logical failure registered during the tests. The speed control responded to the established threshold errors and the preferred dynamically adjustable settings were found to be 0.5mm to 10mm of error in location and 0.5° to 10° in pitch or roll angle. The surgeons were satisfied with the user-interface for graphical guidance and system control. No significant difference in implant alignment, fit and cutting time were found compared with the standard NFC system with standard size computer monitors.
By a wireless link between a CAOS system computer and the cutting instrument (with a graphical touch display screen on board), the patient’s safety and surgeon’s visibility needs were addressed allowing the screen to be aligned with the wound. With a user interface on the saw, and automatic speed and stopping control of the cutting instrument based on navigation, the surgeon is prevented from cutting in the wrong place. This surgeon-actuated but “software cutting jig” fulfils the same functions of cumbersome autonomous or passive surgical robots with their sophisticated servo and haptic interfaces, but with startling utility bringing in the era of the modern “smart” hand-held bone cutting instruments.
Correspondence should be addressed to Diane Przepiorski at ISTA, PO Box 6564, Auburn, CA 95604, USA. Phone: +1 916-454-9884; Fax: +1 916-454-9882; E-mail: ista@pacbell.net
