Biomedical subjects
Publications and source records attributed to W Lorensen.
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Near-real-time frameless stereotaxy registering intraoperative anatomy to a preoperative three-dimensional computer model has been developed for use with in vivo pedicle screw placement. Eight patients underwent thoracolumbar and lumbar spine stabilization surgery using this new technology, and 32 pedicle screws were placed. Three additional patients had 12 pedicle screws removed during revision surgery, and they allowed the authors to estimate the accuracy of this navigational system. Accuracy was determined by comparing pedicle screw position on postoperative computed tomographs for the first eight patients and on preoperative computed tomographs for the latter three patients, with the intraoperative computer trajectory data gathered during operation. In the group of eight patients, all screws were intrapedicular. In evaluating all 11 patients, the overall accuracy was +/- 2 mm, but the greatest error of 5.4 mm was noted in the sagittal plane measurement. During the development phase of this technology, time constraints prolong surgery, but this may be addressed once the tool's accuracy has been confirmed and intraoperative radiographic confirmation becomes unnecessary. In vivo real-time frameless stereotaxy for pedicle screw placement offers promise for the future. Refinements are needed to improve accuracy and address time constraints.
Developed by Orthotronic Medizintechnik GmbH, the so-called Triflexometer, version 3.22 was tested for its reliability and validity in measuring spinal posture and mobility. Reliability studies on 20 healthy subjects have shown this measurement method to be reliable, yet intra- and inter-rater reliability analyses also revealed that even for this healthy population discrepancies in the various measures may occur, both due to differences in compliance as well as fatigue and learning effects, and due to difficulties in stabilization of the normal posture, to a lesser extent due to certain specifics of the measurement technique (placing the markers, guiding the sensor). In total spinal immobility (ankylosing spondylitis), practically identical measurements are found, as is the case in dummy studies. The validity study on 20 healthy subjects found good correlations between the measurements obtaining using the triflexometer and those for double inclinometer, respectively, and that only minor mean value differences occur for the two methods. Also, triflexometer measurements for total anteflexion were found to correlate with those determined with the fingertip-to-floor method, no correlation was present however between the Triflexometer values and the Schober test. Triflexometer measurements performed on 114 healthy subjects of various ages served to prove that the range of spinal movement in the directions measured (sagittal and frontal) will reduce with age. To a lesser extent, this also applies to hip movement. Overall, our findings prove the triflexometer an easy-to-handle system which possesses high reliability and is suitable for valid and objective noninvasive assessment of global and segmental spinal mobility. Triflexometer examinations are highly uncomplicated to implement, and print-outs of the results obtained permit lasting documentation of the present status.
STUDY DESIGN: Frameless stereotaxy with doppler ultrasound and three dimensional computer model registration is assessed in vitro for pedicle screw placement. OBJECTIVE: To identify feasibility of pedicle screw navigation and placement using this technology. SUMMARY OF BACKGROUND DATA: Inaccurate pedicle screw placement can lead to neurovascular injury or suboptimal fixation. Present techniques in pedicle screw placement involve only confirmation of hole orientation. METHOD: Forty-four pedicle screws were placed in lumbosacral models and cadaver specimens. Accuracy was assessed with a computed tomography scan and vertebral cross sectioning. RESULTS: All screws were intrapedicular. Accuracy of anterior cortical fixation was 1.5 mm, with a range of 2.5 mm. CONCLUSION: In vitro frameless stereotaxy is accurate for pedicle screw placement. This technology adds a component of navigation to pedicle screw placement.
Three-dimensional surface reconstruction from computed tomographic (CT) data has been used to plan craniofacial operations. Cephalometric and anthropometric databases were integrated with three-dimensional CT reconstructions to quantitate the skeletal deformity and to assist in the design of the surgical procedure. Interactive techniques were developed to simulate osteotomies and skeletal movements in three dimensions on the computer-generated surface images. The ocular globes were referenced to position the orbital segments; i.e., the osteotomized segments were transposed into normal anatomic relationship with respect to the eyes. The measurements from the computer graphic simulation were used intraoperatively to establish the correct position of the skeletal segments.
A computerized system for processing spin-echo magnetic resonance (MR) imaging data was implemented to estimate whole brain (gray and white matter) and cerebrospinal fluid volumes and to display three-dimensional surface reconstructions of specified tissue classes. The techniques were evaluated by assessing the radiometric variability of MR volume data and by comparing automated and manual procedures for measuring tissue volumes. Results showed (a) the homogeneity of the MR data and (b) that automated techniques were consistently superior to manual techniques. Both techniques, however, were affected by the complexity of the structure, with simpler structures (eg, the intracranial cavity) showing less variability and better spatial correlation of segmentation results between raters. Moreover, the automated techniques were completed for whole brain in a fraction of the time required to complete the equivalent segmentation manually. Additional evaluations included interrater reliability and an evaluation that included longitudinal measurement, in which one subject was imaged sequentially 24 times, with reliability computed from data collected by three raters over 1 year. Results showed good reliability for the automated segmentation procedures.