Heiko Visarius

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 systems 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.

Improved accuracy of pedicle screw insertion with computer-assisted surgery : A prospective clinical trial of 30 patients

Study Design. A prospective clinical trial was done to study the accuracy of pedicle screw placement in 30 consecutive computer-assisted orthopedic surgeries. Objectives. To determine the accuracy and clinical applicability of this new method for pedicle screw insertion. Summary of Background Data. Conventional screw insertion techniques have been associated with high pedicle screw malplacement rates in cadaver studies and clinical studies with postoperative computed tomography evaluation. Methods. Thirty transpedicular, low-back, titanium instrumentations were performed with computer-assisted orthopedic surgery. The accuracy of screw placement was evaluated using a sophisticated computed tomography protocol. Results. The total number of pedicle screws was 174. Of these, 139 (79.9%) could be inserted with computer-assisted orthopedic surgery. The malplacement rate of computer-assisted orthopedic surgery screws was 4.3%. In screws that were not inserted by computer-assisted orthopedic surgery, the malplacement rate was 14.3%. One malplaced screw that had not been inserted with computer-assisted orthopedic surgery caused L4 root paresis. Conclusions. The accuracy of pedicle screw placement using computer-assisted surgery proved to be superior to the accuracy obtained when using conventional techniques.

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.

A Biomechanical Comparison of Cervical Laminaplasty and Cervical Laminectomy with Progressive Facetectomy

The effects of multilevel cervical laminaplasty and laminectomy with increasing amounts of facetectomy on stability of the cervical spine were tested with physiologic loading in nine cadaveric specimens. Cervical spines, levels C2–C7, were tested with physiologic loading in a constraint-free test system, the motion of each body being tracked in a three-dimensional coordinate system. Cervical laminectomy with 25% or more facetectomy resulted in a highly significant increase in cervical motion compared to the intact specimens for the dominant motions of flexion/extension (P < 0.003), axial torsion (P < 0.001), and lateral bending (P < 0.001). Cervical laminaplasty was not significantly different from the intact control, except for a marginal increase in axial torsion. Coupled motion did not change with laminaplasty or laminectomy with progressive facetectomy. As little as 25% facetectomy adversely affects stability after multilevel cervical laminectomy. Cervical laminaplasty avoids this problem, while still affording multilevel decompression. Therefore in patients undergoing cervical laminectomy accompanied by more than 25% bilateral facetectomy, concurrent arthrodesis should be performed.

Man-Machine Interfaces in Computer Assisted Surgery

The clinical potential of computer assisted surgery (CAS) has been more and more widely acknowledged since CAS systems have been introduced into the operating room (OR) theater. Especially the improvements in safety and accuracy are remarkable and strengthen the ties between surgeons and engineers. Tumor stereotaxis was introduced to neurological surgery in the early 1980s, and currently systems with and without robotic navigation are in use for specific medical indications. Recently, solutions for computer assisted orthopedic surgery were developed and applied to various anatomical regions. However, with the establishment of CAS in vivo, a new complex of problems, which was not present in the laboratory setup, was introduced: the man-machine interface. Currently, the complexity of available CAS systems requires the presence of at least one system engineer (often called the “operator”) in the OR. As a consequence, there is no possibility for direct communication between the surgeon and the machine or soft...

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.

Visocelastic shear responses of the cadaver and Hybrid III lumbar spine

Due to the scarsity of cadaver lumbar shear stiffness data, tests on functional lumbar spinal units and a complete lumbar section (T12-L5) were done in both the anterior and posterior directions. Similar tests were performed on the Hybrid III lumbar spine for comparison. Sixteen lumbar motion segments were tested quasi-statically for their viscoelastic properties in a multi-directional (5-axis) spine machine. A hydraulic testing machine was used to carry out dynamic tests including cyclic tests and relaxation tests. In the quasi-static tests the shear response was linear and the anterior stiffness (155 about 90 N/mm) was found to be higher than posterior stiffness (104 about 38 N/mm). In the relaxation tests the load decreased to approximately 60% of its peak value after 30 seconds. Moderate non-linearity was observed in cyclic loading with shear stiffness up to 750 N/mm, depending on the loading rate. Soft tissue only failures occurred in the unconstrained tests at 1290 N (0.5 mm/sec) and 1770 N (50 mm/sec) for anterior loading. Anterior constrained testing failures involved hard tissue at 2800 N and were not rate dependent. The Hybrid III spine elicited higher initial stiffness than cadaver specimens, but was comparable at shear loads greater than 500 N. It also had considerably greater hysteresis than cadaver specimens. For the covering abstract of the conference see IRRD 879189.

A pilot study on computer‐assisted optimal contouring of orthopedic fixation devices

Bending and shaping of longitudinal orthopedic fixation devices like rods and plates is often a difficult and time-consuming process to perform during surgery under sterile conditions. This study presents a novel device for implant contouring and introduces two strategies to obtain parameters necessary for the bending process. The first strategy is based on surgical navigation techniques as established within the framework of computer-assisted orthopedic surgery. Geometrical landmarks, e.g., the location of pedicle screws in a case of posterior spinal fixation, are collected with a three-dimensional pointing device. Subsequently, the final shape of the implant and the associated contouring parameters are calculated. The alternative strategy utilizes a flexible material intended to be used intra-operatively to enable the optimal shape of the implant to be modeled by hand. Contour parameters are calculated from a depth image of this model obtained using an object scanner. Bending of spinal rod systems is used to illustrate both strategies. A newly designed semi-automatic bending machine is proposed to impose the computed deformation on the implant material once parameters are obtained. Integrating the bending device into a system for computer-assisted surgery allows for the interactive control of the contouring process.

Computer-Assisted Insertion of Pedicle Screws

The possible complications of a pedicle screw fixation system include injury to neurologic and vascular structures resulting from inaccurate placement of the instrumentation. In a review of 617 surgical cases in which pedicle screw implants were used, Esses and co-authors reported a overall complication rate of 27.4%. The most common intraoperative problem was unrecognized screw misplacement (5.2%). Fracturing the pedicle during screw insertion and iatrogenic cerebrospinal fluid leak occurred in 4.2% of cases. Such a complication rate is not acceptable in clinical practice. In this paper, we discuss a computer-assisted spine surgery system designed for real-time intraoperative localization of surgical instruments on precaptured images used during surgery. Localization was achieved by combining image-guided stereotaxis with advanced opto-electronic position sensing techniques. The insertion of pedicle screws can be directly monitored by interactive navigation using specially equipped surgical tools. Our preliminary results showed no misplacement of pedicle screw, which have further confirmed the clinical potential of this system.