In this study, we successfully conducted a performance evaluation test of a custom-made haptic interface surgical drill on miniature pigs. The reaction time until spine surgeons recognized penetration by the custom-made haptic drill without the penetration detection function was 0.10–0.22 s. In contrast, the time to detect the penetration of lamina on the drill with the penetration detection function was 0.01–0.02 s with an extremely small error range of 0.005 s. We quantitatively demonstrated that an extremely shorter automatic stop of a surgical drill can be achieved by the integration of haptic technology into spinal drills with a penetration detection function. Furthermore, the distance travelled after penetration with the penetration detection function was significantly shorter than that of the handheld drill with excellent reproducibility. Therefore, we considered that the safety of the haptic drill was substantiated. We substantiated that it is possible to construct the simulator model by the movement data, such as the reaction force, travel distance, travel speed, cutting torque and rotation speed of the drill. Therefore, we demonstrated that the differential signal of steep changes in the reaction force and drilling speed is significant to improve the accuracy of the detection function and automatic stop function. We elucidated the versatility of real haptic technology by evaluating the prototype of the haptic drill.
In this study, 3 spine surgeons drilled the posterior lamina of miniature pigs. Their years of experience differed, ranging from 2 to 22 years (2, 7, and 22 years). The average reaction time was 0.169 ± 0.041 s, and the distance travelled after penetration was 2.982 ± 1.242 mm when using a handheld drill without the penetration detection function. Additionally, the lack of correlation between the detection time and distance indicated that bone drilling using a handheld drill was less reproducible. However, when using the handheld surgical drill with the penetration detection function, the reaction time and the distance after penetration were both improved. The average reaction time to detect penetration and distance after penetration were both significantly shorter than those of the handheld surgical drill without the penetration detection function, with mean differences of 0.049 ± 0.019 s and 2.511 ± 0.537 mm, respectively. This result clearly showed that even if the drill was used by handheld devices, the reaction time and the distance after penetration can be significantly shortened if the real haptics are integrated into the surgical drill.
Interestingly, analysis of the reaction time and the travel distance after penetration of the handheld surgical drill with the penetration detection function showed no statistically significant differences for their average reaction time and the distance travelled after penetration among the surgeons. According to this result, surgeons can recognize penetration extremely quickly with haptic drills regardless of their years of experience. As we have described in the introduction section, gaining surgical experience has thus far been considered very important in reducing the possibility of neurological complications developed by surgical drills. However, it is difficult to gain experience in actual spine surgery without years of experience performing spinal surgery. Therefore, the establishment of a surgical simulator using real haptics technology will be important for young spine surgeons to gain experience to avoid neurological complications by surgical drilling. Several previous reports described the availability of haptic technology for surgical simulators.11–13) Meyer et al. compared the drilling performance by the bone simulator with a haptic system between the trainee resident group and the expert staff surgeon group. They concluded that there were no significant differences in surgical time or the accuracy of the surgical technique. 12) Thus, the use of a spine surgery simulator with a haptic system may be useful for spine surgery education that requires a constant learning curve. Previous reports showed the utility of real haptics technology only for surgical simulators. This study is the first report indicating the accuracy of the penetration detection function and automatic stop function of haptic drills.
In this study, we also proved the accuracy of penetration detection when the surgeon operated the drill in the horizontal direction, which is similar to the actual surgical procedure. It was possible to detect penetration according to the shape of the lamina by recognizing the position by dividing it into 2 mm increments. On the other hand, the position information of the lamina can be moved by the deviation of the spine during the procedure, so over detection may occur as a problem; however, over detection never causes danger to the spinal cord. Currently, we are planning to add alert systems to the penetration detection system. Further refinement of the penetration detection system warrants minimization of the over detection of the penetration.
Furthermore, the concept of using real haptic technology and virtual reality (VR) for robotic surgery has also been developed.13, 14) These systems are controlled with a haptic device that feedbacks the exerted drilling force into the hand of the surgeon in real time. In addition, surgeons can detect the difference in tissue and then perform surgeries more safely and accurately. Real haptic systems are also considered to be an essential technology for the development of robotic surgery for telesurgery.15)
We acknowledge the limitation that we were unable to use human cadavers due to resource limitations. In this study, the drill was used only in a vertical direction against the vertebral lamina of the young miniature pig. However, in actual surgery, the surgeon moves the drill in various directions to the vertebral lamina in various age populations while drilling. Further study for the improvement of this evolutional instrument may warrant the evaluation of the safety and utility of the haptic interface surgical drill in various bone conditions, including osteoporotic bone.