The variability in width, height, and spatial orientation of a spinal pedicle makes pedicle screw insertion a delicate operation. The aim of the current paper is to describe a computer-assisted surgical navigation system based on fluoroscopic X-ray image calibration and three-dimensional optical localizers in order to reduce radiation exposure while increasing accuracy and reliability of the surgical procedure for pedicle screw insertion. Instrumentation using transpedicular screw fixation was performed: in a first group, a conventional surgical procedure was carried out with 26 patients (138 screws); in a second group, a navigated surgical procedure (virtual fluoroscopy) was performed with 26 patients (140 screws). Evaluation of screw placement in every case was done by using plain X-rays and post-operative computer tomography scan. A 5 per cent cortex penetration (7 of 140 pedicle screws) occurred for the computer-assisted group. A 13 per cent penetration (18 of 138 pedicle screws) occurred for the non computer-assisted group. The radiation running time for each vertebra level (two screws) reached 3.5 s on average in the computer-assisted group and 11.5 s on average in the non computer-assisted group. The operative time for two screws on the same vertebra level reaches 10 min on average in the non computer-assisted group and 11.9 min on average in the computer-assisted group. The fluoroscopy-based (two-dimensional) navigation system for pedicle screw insertion is a safe and reliable procedure for surgery in the lower thoracic and lumbar spine.
Deep Dive into Fluoroscopy-based navigation system in spine surgery.
The variability in width, height, and spatial orientation of a spinal pedicle makes pedicle screw insertion a delicate operation. The aim of the current paper is to describe a computer-assisted surgical navigation system based on fluoroscopic X-ray image calibration and three-dimensional optical localizers in order to reduce radiation exposure while increasing accuracy and reliability of the surgical procedure for pedicle screw insertion. Instrumentation using transpedicular screw fixation was performed: in a first group, a conventional surgical procedure was carried out with 26 patients (138 screws); in a second group, a navigated surgical procedure (virtual fluoroscopy) was performed with 26 patients (140 screws). Evaluation of screw placement in every case was done by using plain X-rays and post-operative computer tomography scan. A 5 per cent cortex penetration (7 of 140 pedicle screws) occurred for the computer-assisted group. A 13 per cent penetration (18 of 138 pedicle screws) o
Mobile fluoroscopic device is an integral part of the standard equipment used in orthopaedic surgery to provide real-time feedback of bone and surgical tool positions. One of the disadvantages of this technique include the need for continuous radiation exposure for realtime visual control. For instance, in some specific surgical procedures such as distal locking in standard closed intra-medullary nailing of the femur and tibia, it is well known that this procedure is time-consuming and causes much irradiation to the patient and to the surgical team. In this exemple the surgeon's direct exposure to radiation varies from 3.1 to 31.4 min per procedure and 31 to 51 % of the total irradiation is spent on distal locking alone [1,2,3].
In clinical practice, mobile fluoroscopy device is not only used for distal locking in standard closed intra-medullary nailing for femur and/or tibial fractures, but also for many others surgical procedures. For instance, three other classical procedures are well known to cause much radiation : insertion of pedicle screws in spine surgery for trauma, scoliosis and degenerative instabilities ; osteosynthesis of intra -extra capsular femoral neck fractures and ilio-sacral joint fixation for the treatment of ilio-sacral joint disruption. This paper describes a computer-assisted surgical navigation system based on fluoroscopic X-ray image calibration and 3D optical localizers in order to reduce radiation exposure while increasing accuracy and reliablility of the surgical procedure for implant insertion. We will describe the surgical technique used for pedicle screw placement in spine surgery, before a brief report on other techniques.
Material and Methods :
A three-dimensional optical localizer (Polaris system ; Northern Digital ; Ontario ; Canada) is used to track the position of surgical tools, patient reference and C-arm image intensifier (OEC Medical system ; Courtabeuf ; France) within the region of the operating table (Fig. 1).
Each component is equipped with passive markers that give the position of three distinct tools (patient reference frame ; surgical tools : pointer, sharp tip probe, bradawl and drill guide ; C-arm), with the help of the three -dimensional optical localizer.
Fluoroscopic images are usually distorted. This is due to three factors: the planarity of the image intensifier input screen, the insufficient rigidity of the c-arm and the surrounding magnetic field [4,5]. To correct image intensifier distortions and calibrate images, a calibration grid (equipped with passive markers) is attached rigidly to the input screen of the image intensifier (Fig. 2). The aim of the calibration process is to learn the mapping between image pixels and the “physical” surgical space, so that the computer can generate a virtual projection of the surgeon’s tool axis onto the calibrated X-ray views. The calibration device is fixed to the image intensifier and contains radio-opaque elements arranged on two parallel plates. Radio-opaque elements who are included in the lower plate are used to correct the image distortions and these of the upper one to detemine the x-rays source position (Fig. 2).
To determine the x-ray source position, passive markers are fixed on the calibration device and the three-dimensional optical tracking system is used to localize the fluoroscopic imaging device (Fig. 2,3).
The correction of original images can be effected thanks to the radio-opaque elements of the lower plate projected onto the images (Fig. 4).
We describe here the surgical technique using virtual fluoroscopy in spine surgery for pedicle screw fixation. In spine surgery, the complications associated with misplaced pedicle screws are mostly neurological or vascular. Previous study of surgical procedures have shown a significant rate of incorrect placement of pedicle screws ranging from 15 % to 40 % [6,7].
Virtual fluoroscopy is one of the solution to increase safety of screw placement.
The patient is settled in prone position and the surgeon perform a posterior approach. In a first step, the surgeon attaches the dynamic reference frame to the patient’s bone of interest (in this case : spinous process of the vertebra to be operated on) and aligns the optical localizer’s cameras optimally (Fig. 3). In a second step, the surgeon acquires one X-ray view, just to calibrate the C arm. In a third step, two single X-ray views from A-P and lateral positions are acquired within the area who has to be operated on (Fig. 5). Data are passed on to the workstation computer (Fluologics system, Praxim, France) (Fig. 1). After calibration of the acquired X-rays by the computer, the fluoroscope is turned off and removed from the operating field.
Finally, the calibrated views are displayed on the workstation screen. A computer-generated projection of the surgeon’s surgical tool is also displayed in each view. This is equivalent to its representation under conventional constant fluoroscopic control. A real
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