Abstract
INTRODUCTION
Unicompartmental knee arthroplasty (UKA) can achieve excellent clinical and functional results for patients suffering from single compartment osteoarthritis. However, UKA is considered to be more technically challenging to perform, and malalignment of the implant components has been shown to significantly contribute to UKA failures. The purpose of this investigation was to determine the clinically realized accuracy of UKA component placement using surgical navigation and dynamically referenced tactile-robotics.
METHODS
Pre-op CT, post-op CT, and surgical plan were available for 22 knees out of the first 45 procedures performed using a new tactile-guided robotic system. 3D component placement accuracy was assessed by comparing the pre-operative plan with the post-operative implant placement (desired versus actual). Bone and implant models were obtained from postoperative CT scans taken immediately following the surgery. A 3D to 3D iterative closest point registration procedure was performed and the measured implant position was directly compared to the preoperative plan. Errors were assessed as single axis root-mean-square (RMS) entities.
RESULTS
Femoral component RMS placement errors averaged 1.4 mm/2.6° along any single axis. Tibial component RMS placement errors averaged 1.18 mm/2.14° along any single axis.
CONCLUSION
Using traditional manual instruments, Cobb et al. found average RMS errors of 2.20mm/5.48°. Using the robotic approach with bones fixed, Cobb et al. reported RMS errors of 1.11 mm/2.5°, directly comparable to our results with bones moving freely during surgery. Varus/valgus femoral component alignment and posterior tilt of the tibial component are within the accepted range to prevent excessive edge loading, leading to tibial plateau collapse and/or excessive wear. Dynamically-referenced tactile robotics provide a new tool to accurately prepare bone with minimally invasive approaches. Our results suggest excellent UKA implant placement accuracy can be achieved, comparable to that demonstrated for statically referenced tactile robotics. The patients were the first group from a single surgeon using this technique, suggesting good implant alignment is achieved in what normally would be considered a learning phase. Finally, these patients were treated with the first approved version of this new tool, suggesting further refinement of this robotic technology will enhance the accuracy and usability of this tool.
