Planning and insertion of pedicle screws with computer assistance

Transpedicular screw fixation relies on thorough knowledge of the pedicular anatomy and a reliable intraoperative technique. To enhance the safety and accuracy of screw insertion, computer-assisted systems have been introduced. Our in vitro study investigated the potential benefits of such a system for the preoperative planning and the intraoperative visualization. In part 1, the potentially possible range of screw paths (trajectories) through lumbar pedicles was analyzed. In part 2, the accuracy of actual pedicle-hole preparation with and without preoperative planning was assessed. It was shown that, especially in the lower lumbar regions, the possible range of trajectories is considerable, with inclinations of < or = 40 degrees in the transverse plane and a range of angulation in the sagittal plane of > 20 degrees. The computer assistance in preparation of 100 pedicle holes resulted in cortex perforation in only one case. Computer assistance therefore may be used as a valuable tool to minimize the risks of transpedicular screw insertion. It furthermore may assist in determining the desired screw orientation and length and transform this planning into the intraoperative pedicle-hole preparation.

Accuracy of computer-assisted pedicle screw placement. An in vivo computed tomography analysis

STUDY DESIGN

A computer-assisted planning and visualization system (the Orthopaedic Surgery Planning System) was tested for pedicle screw insertion in vivo.

OBJECTIVES

To evaluate the system's applicability for regular intraoperative use and its accuracy for pedicle screw placement in vivo.

SUMMARY OF BACKGROUND DATA

Pedicle screw placement poses considerable anatomic and biomechanical risks. The reported rates of screw misplacement with conventional insertion techniques are unacceptably high. It previously has been shown in vitro that computer assistance offers the potential to decrease the number of screws perforating the pedicular cortex.

METHODS

The accuracy of 162 pedicle screws inserted with the Orthopaedic Surgery Planning System was assessed by means of postoperative computed tomography evaluation. Reconstructions of the horizontal, frontal, and sagittal planes were analyzed. Cortex perforations were graded in steps of 2 mm.

RESULTS

The cortex was perforated in 2.7% of pedicles. Complete preoperative computed tomography scanning of the levels to be operated on is essential to allow for a precise image reconstruction. Initial difficulties in applying the system contribute to the malplacements. A learning curve for general handling of the Orthopaedic Surgery Planning System was observed.

CONCLUSIONS

The system provides a safe and reproducible technique for pedicle screw insertion. Other applications in the field of spine surgery are under evaluation.

Image-guided computer-assisted spine surgery: a pilot study on pedicle screw fixation

As the pedicle offers a strong point of attachment to the spine, several instrumentation systems using screws that go through the pedicle into the vertebral body have been developed to provide internal stability. All pedicle screw systems share the risk of damage to adjacent neural structures as a result of improper screw placement. A computer-assisted system allowing precise preoperative planning and real-time intraoperative interactive image localization has been implemented for spine instrumentation to optimize transpedicular spine fixation. A validation study was performed in an in vitro set-up drilling 20 pedicle pilot holes in lumbar vertebrae. An analysis in 77 histological cuts showed an ideal location in 70 with no case of injury to the pedicle cortex. We discuss initial clinical experience on cases of posterior lumbar stabilization. Interactive computer-assisted spine surgery provides an accurate and safe approach for transpedicular screw fixation and may provide a useful tool for optimization of spine surgery.

Clinical evaluation of a system for precision enhancement in spine surgery

Most techniques in segmental spinal fixation surgery rely on the identification of predefined targets with the help of anatomical landmarks and on intraoperative use of image intensifiers. However, because there is no direct link between the image information, the accessible spinal anatomy, and the action of surgical instruments several potential problems and possible complications are still involved. A novel system for spinal surgery has been designed allowing for the real-time, intraoperative localization of surgical instruments in medical images. In practice this was achieved by combining image-guided stereotaxis with advanced optoelectronic position sensing techniques. Modules were developed for image data processing, surgical planning and simulation, and various intraoperative procedures. A detailed validation of the system was performed indicating an overall accuracy to be better than the slice distance of the spinal image used. In an in-vitro setting 20 pilot holes for pedicle screws were prepared in human cadaveric lumbar spines. An analysis in 77 histological cuts showed an ideal location in 70 and only minor cortex engagement in seven sections. In vivo the system has been successfully applied in three posterior low lumbar stabilizations with overall 15 transpedicular screws. RELEVANCE--:This article focuses on the clinical evaluation of a computer-assisted surgery system and its application to the operating theatre for transpedicular fixation of the spine. The given approach effectively keeps the surgeon 'in the loop' and requires only minor modifications of the established surgical techniques and associated instruments. The results of this study indicate that advanced computer-assisted techniques may significantly improve the accuracy and safety of surgical interventions of the spine. The proposed technique may in future be adapted to other applications in orthopaedic surgery.

Computer-aided fixation of spinal implants

Medical imaging provides an important basis for modern diagnosis as well as for preoperative planning of surgical procedures. However, information gained cannot be transferred directly into the operating room. Furthermore, the safety and accuracy of the surgical intervention would be improved by interactive navigation of surgical instruments. These features are provided by the system for computer-aided fixation of spinal implants described in this paper.

Real-time image reconstruction system for interventional magnetic resonance surgery

Interventional surgery techniques under the control of fast acquired magnetic resonance (MR) images may become important in interventional radiology in the near future. One of the components needed for an interventional MR scanner is the real-time reconstruction of the acquired MR images. However up to now no real-time reconstruction systems are readily available for MR images. Therefore a reconstruction device was developed, which allows reconstruction and display of MR images with a delay of less than 50 ms. Additional to the high performance, the main characteristics of the presented device are its full compatibility with different MR acquisition techniques and its moderate cost. The device can be operated with most types of commercial scanners. It is especially suited for interventional MR systems but has also applications with conventional MR scanners.