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Study Design/setting: Retrospective study., Objective: The purpose of this study was to use multidimensional analysis with a computed tomography (CT)-based navigation system to measure the outer cortical diameter and the maximum screw trajectory length of the pedicle of the thoracic and lumbar regions of the spine in adolescent idiopathic scoliosis (AIS) patients. Another objective was to identify pedicles that require cautious insertion of screws., Summary of Background Data: Pedicle diameter in AIS patients was narrower on the concave side of the scoliotic curve. Many researchers have measured pedicle diameter and length of AIS patients by using standard CT or magnetic resonance imaging (MRI), but only few have used 3-dimensional imaging, especially CT-based navigation., Methods: Fifteen patients with right-side thoracic AIS who underwent pedicle screw fixation were studied. A CT-based navigation system was used to measure the pedicle diameter, defined as the widest outer cortical diameter at the narrowest part of the pedicle. Moreover, the maximum pedicle screw trajectory length was measured as the distance between the posterior cortical entry point of the pedicle screw and the anterior vertebral cortex in line with the axis of the pedicle between T1 and L5. In addition, the values of each parameter taken using the CT navigation system and the standard axial CT were compared., Results: Pedicles on the concave side of the main thoracic curve apex and proximal thoracic curve tended to have the narrowest diameters. The mean length of the longest screw that could be fixed was longer on the right side, except for T8 and T9. Our data showed screw size feasibility as follows: 25 or 30 mm screws were feasible from T1 to T5; 30 or 35 mm screws, from T6 to T12; and 35 or 40 mm screws, from L1 to L5. Pedicle diameter measured by the CT navigation system was larger than that measured by standard axial CT. Left-side pedicle length measured by the CT navigation system was lesser than that measured by standard axial CT., Conclusions: Pedicle diameter in patients with AIS is narrower on the concave side of the scoliotic curve, and therefore, caution should be exercised during screw insertion on the concave side.

Study Design: Retrospective clinical study., Objective: To assess the accuracy of multilevel registration for skip pedicle screw placement during image-guided, computer-assisted spine surgery, in the setting of adolescent idiopathic scoliosis (AIS)., Summary of Background Data: Computerized frameless stereotactic image-guidance has been used recently to improve pedicle screw placement accurately and safety during spine surgery. Because of possible intervertebral motion and usual difference in patients' position between preoperative imaging and surgery, the imaging model and the surgically exposed spine may be significantly discordant. Consequently, current protocols suggested separate registration of each spinal level (single-level registration) before respective pedicle screw placement, a time-consuming process. Moreover, although multilevel registration for lumbar spine has been reported, and that for thoracic spine has not., Methods: A total of 19 patients (1 male and 18 females; mean age, 13.9 years) with AIS who underwent multilevel registration for skip pedicle screw placement were included. Variables including surgical time, blood loss, preoperative and 2-year postoperative Cobb angle, correction rate, and postoperative screw position by computed tomography image were evaluated. Mean registration error after point merge and again after surface merge were recorded for each consecutive vertebra of each case., Results: Mean surgical time was 310 minutes (range, 168-420 min). Mean blood loss 1138 g (range, 300-2300 g). Cobb angle before operation and at 2 years postoperation was 62.4 degrees (43 degrees-100 degrees) and 21.6 degrees (9 degrees-42 degrees), respectively. Mean correction rate 66.2% (39.7%-84.5%). Total 265 screws were inserted with computed tomography-based navigation system. Pedicle violation was observed in only 4 screws (1.5%). No neurovascular complication occurred. After point merge, average Mean registration error of all cases was 1.69 +/- 0.52 mm, and after surface merge was 0.51 +/- 0.16 mm., Conclusion: Multilevel registration may decrease operative time without compromising accuracy of pedicle screw placement afforded by this technique in the setting of AIS.

Background Context: Cervical pedicle screw (CPS) insertion is technically demanding and carries a risk of serious neurovascular complications when screws perforate. To avoid such serious risks, we currently perform CPS insertion using a computed tomography (CT)-guided navigation system. However, there remains a low probability of screw perforation during CPS insertion that is affected by factors such as CPS insertion angle and anatomical pedicle transverse angle (PTA).Purpose: This study aimed to understand the perforation tendencies of CPS insertion angles in relation to anatomical PTA.Study Design: This is a retrospective chart review.Patient Sample: The study enrolled 151 consecutive patients (95 men and 56 women, with a mean age of 64.6 years).Outcome Measures: Anatomical PTA and CPS insertion angles were evaluated by axial CT images.Methods: The medical records of 151 consecutive patients who underwent CPS insertion using a CT-based navigation system were reviewed. We examined the relationships between PTA and CPS insertion angle on axial CT images according to vertebral level.Results: The average preoperative PTA at each vertebral level was 32.1° for C2, 41.5° for C3, 41.0° for C4, 39.4° for C5, 34.4° for C6, and 27.3° for C7. Corresponding CT-determined pedicle screw insertion angles were 24.9°, 31.3°, 28.7°, 27.8°, 28.0°, and 26.0°, respectively. The CPS insertion angles at C2-C6 were significantly smaller than those for PTA (p<.01). In evaluations of angle thresholds from C3 to C5 that predicted a higher risk of perforation, the receiver operating characteristic curve analysis determined CPS insertion angles of <24.5° and >36.5° for the identification of lateral and medial perforations, respectively.Conclusion: For CPS insertion into the C3-C5 pedicles using CT, there is an increased likelihood of lateral or medial perforation for insertion angles of <24.5° or >36.5°, respectively. [ABSTRACT FROM AUTHOR]

Background: Instability of the occipitocervical junction can present challenging surgical problems because of the unique anatomic and biomechanical characteristics of this region. The purpose of this study was to evaluate the long-term surgical results and usefulness of a computed tomography (CT)-based navigation system for the occipitocervical reconstruction. Methods: Twenty-three patients (10 men, 13 women; mean age at surgery 57.9 years; mean follow-up periods 52.9 months) with occipitocervical junction disorders were treated by occipitocervical reconstruction using pedicle screws, aided by a CT-based navigation system. Roentgenologic measurement and clinical evaluation were performed before surgery and at final follow-up. Postoperative CT and plane radiographs were used to determine the accuracy of screw placement. Results: Mean atlantodental interval and Ranawat value were significantly improved (P<.05), and mean clivoaxial angle was increased after surgery and maintained at final follow-up. Mean Japanese Orthopedic Association score before and at final follow-up was 7.1 ± 4.4 and 11.3 ± 3.5 points, showing significant improvement (P = .005). Fourteen patients (61%) improved more than one Ranawat grade. Six of nine patients (67%) in class IIIB were improved. On the other hand, nine patients (39 %) remained at the same class at final follow-up. A total of 88 pedicle screws were inserted into cervical and upper thoracic pedicles using the navigation system, and only one screw (1.1 %) showed major pedicle wall perforation. Solid union was achieved in all 23 patients. Conclusions: Occipitocervical reconstruction using pedicle screws provided a high fusion rate and maintained alignment in the occipitocervical region. The computer-assisted navigation system was a useful tool for accurate and safe pedicle screw insertion. [ABSTRACT FROM AUTHOR]