Abstract
Introduction
Computer aided surgery aims to improve surgical outcomes with image-based guidance. Navigated Freehand bone Cutting (NFC) takes this further by eliminating the need for cumbersome mechanical jigs. Multiple previous experiments on plastic and porcine bones, performed by surgeons with different level of expertise, suggested that the NFC technique was feasible. This study pushes NFC further by using the technique to perform complete total knee replacement (TKR) surgeries on cadavers (including implant cementing of tibia and femur).
Materials and Methods
A single surgeon performed a series of TKR surgeries on full cadaveric legs. Cruciate sacrificing implants were selected because these were considered more challenging for a freehand cutting approach due to the extra number and complexity of the cuts needed around a posterior stabilizing post recess when present.
A proprietary NFC prototype system was used, with real time graphics to indicate where/how to cut the bone without jigs. The system comprised a navigated smart oscillating saw, reciprocating saw and drill without any of the conventional jigs typically used in TKR.
The tasks performed included (and were grouped) to include pre-surgical planning, incision, placement of navigation pins & markers on tibia and femur, bone registration, marking and cutting, cut surface digitization (for quality assessment), implant placement and cementing, assessment of implant fit and location, and pin removal and wound closing.
Results
Experiments ran smoothly without software, hardware, or workflow (logic) failures. One tibia required re-registration after failing the registration validation process, and one reflective ball on the smart saw had to be replaced during surgery due to a defective fastening. Overall average surgery time was 1 hour and 20 minutes. The cutting process took the most time (31% of total time) followed by cementing and bone registration (14% and 12%, respectively). Surface smoothness of the bone cuts on human cadavers was better than what was previously obtained for synthetic bone.
Discussion and Conclusion
The results indicate that Navigated Freehand Cutting technology could eventually be used on patients, as surgical time, implant alignment, cut quality, and other metrics are consistent or better than those of conventional approaches, even with this prototype system. New computer-human interfaces under development are expected to reduced cutting, registration, digitization times, promising a faster overall surgery. We speculate that Navigated Freehand Cutting (NFC) is no longer a dream, no longer just feasible, but on the way to clinical trials not too far in the future.
