Marwan Sati

Fluoroscopy as an imaging means for computer‐assisted surgical navigation

OBJECTIVE Intraoperative fluoroscopy is a valuable tool for visualizing underlying bone and surgical tool positions in orthopedic procedures. Disadvantages of this technology include the need for continued radiation exposure for visual control, and cumbersome means of alignment. The purpose of this article was to highlight a new concept for a computer-assisted freehand navigation system that uses single intraoperatively acquired fluoroscopic images as a basis for real-time navigation of surgical tools. MATERIALS AND METHODS Optoelectronic markers are placed on surgical tools, a patient reference, and the fluoroscope to track their position in space. Projection properties of the fluoroscope are acquired through an initial precalibration procedure using a tracked radiopaque phantom grid. Corrections are applied to compensate for both the fluoroscopes image intensifier distortions and the mechanical bending of the C-arm frame. This enables real-time simulation of surgical tool positions simultaneously in several single-shot fluoroscopic images. In addition, through optoelectronically tracked digitization of a target viewpoint, the fluoroscope can be numerically aligned at precise angles relative to the patient without any X-ray exposure. RESULTS This article shows the feasibility of this technology through its use in cadaver trials to perform the difficult task of distal locking of femoral nails.

Computer-Assisted Fluoroscopy-Based Reduction of Femoral Fractures and Antetorsion Correction

OBJECTIVE Intra-operative fluoroscopy is a valuable tool for visualizing underlying bone, implant, and surgical tool positions in orthopedics. It has brought about the minimally invasive surgical technique of intramedullar nailing to fix femoral shaft fractures. However, the limited field of view and two-dimensional property of fluoroscopic images aggravate intra-operative control of surgical parameters. The purpose of this article is to introduce a surgical navigation system based on fluoroscopy that provides missing information for the procedure of femoral fracture fixation. MATERIALS AND METHODS Optoelectronic markers are placed on a surgical drill, involved bone fragments, the femoral nail, and the fluoroscope to track their positions. Projection properties of the fluoroscope are acquired through an initial precalibration. The relative positions of bone fragments, implants, and surgical tools are displayed superimposed simultaneously and in real time on multi-planar intra-operative fluoroscopic images. This is achieved by computer simulation of X-ray projections that have taken place with acquisition of the fluoroscopic images. In addition, a method has been developed that allows contactless measurement of three-dimensional anatomic landmarks, based on their representation in fluoroscopic images. In combination with optoelectronic tracking, this enables dynamic calculation of important surgical parameters such as femoral antetorsion. RESULTS A pilot surgery showed that fracture reduction can benefit from the developed computer-assisted method. An in-vitro study on computer-assisted measurement of femoral antetorsion demonstrated the high degree of precision of this technique.

Novel Computer-Assisted Fluoroscopy System for Intraoperative Guidance : Feasibility Study for Distal Locking of Femoral Nails

Objectives Orthopaedic procedures that use fluoroscopy require intraoperative mental navigation of the surgical tools in a three-dimensional space. Moreover, because of their reliance on real-time monitoring, such procedures are frequently associated with increased x-ray exposure. The goal of this study was to develop a computer-guided surgical navigation system based on fluoroscopic images that not only facilitates direction of surgical tools within anatomy, but also provides constant feedback without the need for radiologic updates. To evaluate the feasibility of the new technology, the authors used it on cases requiring distal locking of femoral nails. Methods The hardware components of the system include an instrumented C-arm, optoelectronic position sensor, stereotactic tools, and custom-made software. Computer integration of these devices permitted C-arm alignment assistance and real-time navigation control without constant x-ray exposure. The nails were locked in a variety of media, including plastic femurs, dry human femoral specimens, human cadavers, and one clinical case. Unreamed femoral nail sizes ranged from 9/340 to 12/400. Radiographs were taken to confirm that screws were positioned correctly, and fluoroscopic time associated with the locking procedure was recorded. Results All distal holes were locked successfully. In eight (11 percent) of seventy-six holes, the drill bit touched the canal of the locking hole, albeit with no damage to the nail and no clinical consequences. The fluoroscopy time per pair of screws was 1.67 seconds. Conclusions The developed system enables the physician to precisely navigate surgical instruments throughout the anatomy using just a few computer-calibrated radiographic images. The total radiation time per procedure can be significantly reduced because additional x-ray exposure is not required for tool navigation.

Clinical integration of computer-assisted technology for arthroscopic anterior cruciate ligament reconstruction

Anterior cruciate ligament (ACL) reconstruction with an autogenous graft through the use of a minimally invasive endoscopic approach has become the standard in ACL replacement. The arthroscopically assisted technique causes minimal trauma and can sometimes be performed on an outpatient basis. There have been, however, alarming reports of high misplacement rates of these grafts. These misplacements can partially be attributed to the restricted local view provided by arthroscopy, which does not give the surgeon a global overview of ligament position with respect to knee anatomy. Thirty-degree endoscopes, lens distortions, and the difficulty of judging depth from the 2-dimensional (2-D) view makes mental orientation of internal structures with respect to desired reattachment sites difficult. Another problem is the lack of a general consensus on the best type of graft and on the proper placement of these grafts. As a result, there is a rather large variety of surgical techniques and a variety of different graft types. To help solve these problems, we have developed a computer-assisted system to aid surgeons in planning and intraoperative placement of ligament grafts.

Restricted surface matching: a new approach to registration in computer assisted surgery

Since the first introduction of tumor stereotaxis to neurological surgery in the early 1980s, computer assisted surgery (CAS) has been applied to several medical fields. An important common issue for all CAS systems is the registration between preoperative data (e.g. computed tomography (CT), magnetic resonance (MR) images, ...) and intraoperative data. In our application the objective is to obtain position information of medical tools with respect to CT images of bony structures. We describe in this paper a new approach for the registration of preoperative CT images with the patient in the operating room. The method, that we named ‘restricted surface matching’, is a fast, accurate, and robust surface matching based method.

Performance and Robustness of Automatic Fluoroscopic Image Calibration in a New Computer Assisted Surgery System

In order to improve the clinical usefulness of computer-assisted fluoroscopic navigation, a new algorithm to automatically determine the calibration of fluoroscopic images has been developed. This is a challenging task since the intraoperative images acquired from fluoroscopic systems are often poor, making detection of the calibration grid difficult. Several feature-based methods have been implemented to perform bead detection for automatic detection of the calibration grids. The algorithms include support for multiple fields of view, a feature not supported on any computer assisted systems to date. In order to evaluate the performance of the algorithms, special phantoms were made and a cadaver study was performed to challenge the algorithms. One hundred images were acquired using three different C-Arms (OEC 9600, OEC 9800 and Philips BV-300+) using two different fields of view (nine and twelve inch). The chosen method successfully registered the images in ninety-six of the cases. The images that were not successfully registered were of limited clinical value anyway due to the very poor image quality.

A Transcutaneous Bone Digitizer for Minimally Invasive Registration in Orthopedics: A Real-Time Focused Ultrasound Beam Approach

Computer-guided navigation of surgical tool position in computer-assisted orthopedic systems requires the registration of computer tomographic (CT) images with underlying bone. This process is presently performed by manually digitizing points on bone with a pointer and aligning them to a preoperative CT scan. We propose the use of ultrasound to obtain points on bone transcutaneously. A custom-made A-mode probe features a modular lens focusing system and a one-step calibration method. A stable and precise echo detection algorithm is also implemented. The accuracies of three signal detection algorithms—standard deviation, cross-correlation (XCORR) and short-time Fourier transform—were compared using a known reflected signal. XCORR showed the most accurate and stable operation. To test our method of obtaining bone surface points, a plastic model of the fourth human lumbar vertebra was CT scanned and then immersed in a water bath. Six surface registrations of the vertebra using an accurate pointing device were compared to ten registrations obtained using the US probe (using the XCORR algorithm). Students T-test showed no significant difference in error between the two methods, proving that ultrasound registration, using our method, is equivalent to the more conventional pointer method.

Computer-Assisted Anatomical Placement of a Double-Bundle ACL through 3D-Fitting of a Statistically Generated Femoral Template into Individual Knee Geometry

Femoral graft placement is an important factor in the success of ACL-reconstruction. Besides improving the accuracy of femoral tunnel placement, Computer Assisted Surgery (CAS) can be used to determine the anatomic location. This requires a 3D femoral template with the position of the anatomical ACL-center, based on endoscopical measurable landmarks. This study describes the development and application of this method. The template is generated through statistical shape analysis of the ACL-insertion, with respect to the anteromedial- (AMB) and posterolateral bundle (PLB). The data is mapped onto a cylinder and related to the intercondylar notch surface and the cartilage border on the lateral notch wall (n=33). The template was programmed in a computer-assisted system for ACL-replacement and validated. The program allows real-time tracking of the femur and interactive digitization under endoscopic control. In a wizard-like fashion the surgeon is guided through steps of acquiring the landmarks for the template alignment. The AMB- and PLB-center are accurate positioned within 1-3 mm of the anatomic insertion-centers in individual knees.

Computer-assisted technology for spinal cage delivery

The application of spinal interbody cages as an adjunct to spinal fusion may be regarded as common surgical practice for a number of spinal interventions. Morbidity from surgical approaches as well as learning curves for planning of cage insertion and the actual in vivo application may be considerable, however. On the other hand, computer-assisted surgery (CAS) technologies have been successfully introduced into the field of orthopaedic surgery and may be regarded as routine, at least for the area of pedicle screw insertion. The present study evaluates the potential of computer-assisted technologies in assisting spinal cage application, (ie, the Bagby and Kuslich cage). It shows that technological priciples are available to accurately plan cage insertion, including the preoperative demonstration of distraction and alignment consequences for the entire segment. Furthermore, during surgery, the surgeon may be guided to the appropriate spinal segment, followed by precise execution of the preoperative plan. These features are combined with endoscopic techniques and are available for in vitro training of spinal surgeons. For in vivo applications, however, matching and registration procedures have to be refined to enable detection of bony structures, especially from a single anterior surgical approach. For this purpose, various possibilities, such as the use and integration of ultrasound, are under evaluation.

Double-Bundle Anatomic ACL-Reconstruction with Computer Assisted Surgery: An In-Vitro Study of the Anterior Laxity in Knees with Anatomic Double-Bundle versus Isometric Single-Bundle Reconstruction

The current standard technique to reconstruct ruptured anterior cruciate ligament (ACL) is through an isometric single-bundle graft. However, the ACL has a two-bundled nature, with the anteromedial bundle (AMB) most tight in flexion and the posterolateral bundle (PLB) near extension. Therefore a double-bundle, anatomically placed, graft is expected to provide better stability over the complete range of motion. The anterior laxity was tested in various flexion angles in knees with anatomic double-bundle and isometric single-bundle reconstruction. Anatomic femoral graft placement was performed using Computer Assisted Surgery (CAS) with the AMB-graft fixated in 90° of flexion and the PLB in 20°. Near extension the double-bundle technique caused no significant laxity change compared to a 2.1 mm (34%) increase in single-bundle reconstructed knees. In 90° of flexion the laxity increase was nearly similar. Over the complete range of motion the anatomic double-bundle technique results in a better functional reconstruction, at the cost of a higher AP-error near extension.