ABSTRACT
Transpedicular screw placement is a high-risk procedure routinely performed in spine surgery. To decrease the rate of complications, it is necessary to find innovative solutions to assist the surgeon during screw insertion so as to avoid the chance of mispositioning. In this study, we developed a new drilling system able to estimate the mechanical properties of drilled tissues. Several investigations show that cortical bone requires a high level of thrust force and torque during drilling compared to trabecular bone. To implement an algorithm for bony breakthrough detection, a new drilling system has been built together with a mechanical support to drill the pedicle along a pre-planned trajectory. The mechanical support is equipped with a smart rotative drill that embeds force and position sensors. Ten human vertebral segments have been used to test the surgical platform, for percutaneous bone drilling. 10 transpedicular holes from L1 to L5 have been performed bilaterally. The holes were further evaluated by computed tomographic scans to measure bone density in the cortical and in the trabecular layers. To compare bone density with the bony mechanical impedance two new parameters (DHU and DPAI) have been introduced. The results show that in 18 out of 20 cases the D values of bone density and mechanical impedance, related to the same bone transition, differ less than 10%. The proposed system is thus able to evaluate the variation of bone density of the cortical and the trabecular layer using impedance. Therefore, it is possible to use the described system to increase the accuracy of transpedicular screw placement.
Subject(s)
Bone Screws , Bone Density , Electric Impedance , Humans , Pilot Projects , Spinal FusionABSTRACT
Minimally Invasive Spine Surgery (MISS) procedures for the treatment of spinal pathologies have experienced exponential growth due to improved techniques and decreased trauma to the patient. Several MISS procedures that require the use of a trans-pedicular cannula as a guiding tool for pedicle screw placement, delivery of biomaterials to the vertebral body or injection of biologics to the disc space have been described. Although these are clear advantages of MISS, the limited dissection and exposure may reduce the accuracy and stability of operation and make spine surgeons rely heavily on intraoperative fluoroscopy, raising concerns over the level of radiation exposure. Robot-assisted minimal invasive surgery has aroused more attention for its high precision and stability, minimizing risks of damage to neurovascular structures and diminishing harmful exposure to ionizing radiation. The aim of this paper is to describe and characterize a new surgical positioning system for for robotic assisted MISS. The system is conceived to be integrated in a surgical platform capable of supporting the surgeon in a new procedure to treat degenerative intervertebral disc disease. For this purpose, it is necessary to orientate a cannula in order to guide the bone drill along a planned route, to access the intervertebral disc through the pedicle and endplate. In particular, we describe a mechanism that percutaneously guides a cannula towards the intervertebral disc based on the acquisition of few fluoroscopic images. The design of the positioning system, with its features and constrains imposed by the presence of instrumentation and medical staff in the operating room, as well as the software for trajectory planning during surgery, are here described.
ABSTRACT
In this paper we present a model for calculating the electric field, and its spatial derivatives, produced by arbitrarily shaped, oriented and placed coils carrying time-varying currents. The model has been validated by comparing its results with those obtained using FEM simulations. The model provides a simple and fast computation framework to investigate the electromagnetic stimulation of neural tissues. Some example applications are also provided.
