Análisis morfométrico del atlas por tomografía computada para la colocación de tornillos trans-masas laterales / Morphometric analysis of the atlas by computed tomography for the placement of lateral transmass screws

Objetivos: Realizar un análisis morfométrico del atlas por tomografía computada, determinando los valores promedio, medianos, y de variabilidad de dicha vértebra para la correcta colocación de tornillos trans-masas laterales. Introducción: Existe una significativa variabilidad interpersonal en los aspectos morfológicos del atlas, y dada su proximidad a estructuras neurovasculares (arteria vertebral, médula cervical, raíz de C2), hacen mandatario un exhaustivo planeamiento prequirúrgico para la elección de la técnica de artrodesis, tipo de tornillos a utilizar, y su trayectoria. Material y métodos: Se realizó un estudio de diseño de tipo exploratorio, descriptivo, observacional, retrospectivo, transversal. Se revisaron 99 tomografías computadas de la columna cervical. Se midieron parámetros morfométicos y angulaciones desde un "punto de entrada" en la masa lateral de C1, que fueron llamados A, B, C, D, E, F, G y H. Las mediciones de los parámetros a estudiar fueron realizadas con el programa RadiAnt DICOM Viewer (64-bit) y posteriormente volcadas a una ficha de registro de datos. Discusión: La distribución según género fue de 34 varones y 65 mujeres. Se encontró una diferencia estadísticamente significativa no solo en lo referente al género (masculino vs femenino; parámetros A, B, C, D, F, G, H p-valor < 0,05) de los parámetros medidos, sino también según lateralidad (derecha vs izquierda; parámetros C, E, F, G p-valor < 0,05). La investigación propone además la generación de una base de datos con información morfométrica del atlas. Conclusión: Existe una diferencia estadísticamente significativa en las propiedades morfológicas del atlas, tanto en lo relativo al género (masculino vs femenino), como en la lateralidad (derecha vs izquierda). Es por ello que el presente estudio enfatiza en la importancia de la realización prequirúrgica de una tomografía computada de la columna cervical superior para garantizar una efectiva y segura instrumentación a éste nivel, según el largo, ancho y trayectoria de los tornillos a utilizar.

Objectives: To morphometrically analyze the atlas, using computed tomography, thereby defining mean, median and variability values of C1 for the correct placement of lateral mass screws. Introduction: Significant interpersonal variability exists among the various morphological characteristics of the atlas. Given the structure's close relationship to neurovascular structures like the vertebral arteries, cervical spinal cord, and cervical roots, exhaustive pre-surgical planning becomes mandatory. Such planning assists in the choice of arthrodesis technique, and the dimensions and trajectory of screws. Material and Methods: A retrospective, observational study was performed, for which the computed tomography (CT) scans of 99 cervical spines were reviewed. Morpho-metric parameters and angulations were measured from an "entry point" in the lateral mass at C1; these parameters were alphabetically labeled from A through H. The RadiAnt DICOM Viewer (64-bit) program was used to measure all parameters of interest, the values of which then were entered into a data collection file.Discussion: By gender, there were 34 men and 65 women. A statistically-significant difference was found between the two genders for all parameters except parameter E (all p-values < 0,05), and between the two sides (right vs. left) for parameters C, E, F, and G. Our results argue for the creation of a general database containing morphometric information on the atlas. Conclusion: Statistically-significant differences exist between men and women, and from right to left, among the morphometrical features of the atlas. This underscores the need for careful preoperative surgical planning, including the use of CT scanning to estimate optimum screw lengths and trajectories.

Assessment of C1 lateral mass screw trajectory and position by plain radiographs / 局解手术学杂志

Objective The aim of this study was to provide methods for predicting ideal trajectory and position of C1 lateral mass screw (C1 LMS)from plain radiographs.Methods A total of 40 consecutive subjects (with 79 screws)who had undergone C1 LMS placement were enrolled.To evaluate the C1 LMS position,the positions of screw head and tips on anteroposterior radiographs,screw length,and height on lateral radiograph were graded as 0°,Ⅰ°,and Ⅱ°,respectively.On the postoperative computed tomography images,the lateral mass (LM) perforation,screw-thread engagement percent(%),bicortical fixation,extruded screw length,and violation of adjacent joints were analyzed. Results Screws with tip located medial to LM(tip 0)showed LMperforation in all cases.Polyaxial head located within the LM(head 0)or crossing the lateral margin of the LM(head Ⅰ)showed no LMperforation.Screw-thread engagement percent was the highest with head Ⅰ-tip Ⅰ (medial half of LM)position (97.6%),followed by head 0-tip Ⅰ (90.5%)and head Ⅰ-tip Ⅱ (lateral half of LM)(86.4%). Screws longer than the posterior half of C1 anterior arch (AA)showed bicortical fixation in all cases with mean extruded screw length of 1.9 mm.Adjacent joint was not violated in 98%,with the screw height below half of C1 AA.Conclusion On an anteroposterior radiograph, a C1 LMS with the screw head located on the lateral margin of the LMand with the screw tip in the medial half of the LMresulted in the safest and longest trajectory.On lateral radiograph,a screw tip that is placed within the anterior-inferior quadrant of the C1 AA results in safe bicorti-cal fixation without injury to the adjacent structures.These plain radiographic findings may be helpful bothpostoperatively and intraoperatively for assessing the trajectory and length of the screw.

Comparison of Outcomes after Atlantoaxial Fusion with Transarticular Screws and Screw-Rod Constructs

OBJECTIVE: The purpose of this study was to compare the radiological and neurological outcomes between two atlantoaxial fusion method for atlantoaxial stabilization; C1 lateral mass-C2 pedicle screws (screw-rod constructs, SRC) versus C1-2 transarticular screws (TAS). METHODS: Forty-one patients in whom atlantoaxial instability was treated with atlantoaxial fixation by SRC group (27 patients, from March 2005 to May 2011) or TAS group (14 patients, from May 2000 to December 2005) were retrospectively reviewed. Numeric rating scale (NRS) for pain assessment, Oswestry disability index (ODI), and Frankel grade were also checked for neurological outcome. In radiologic outcome assessment, proper screw position and fusion rate were checked. Perioperative parameters such as blood loss during operation, operation time, and radiation exposure time were also reviewed. RESULTS: The improvement of NRS and ODI were not different between both groups significantly. Good to excellent response in Frankel grade is shown similarly in both groups. Proper screw position and fusion rate were also observed similarly between two groups. Total bleeding amount during operation is lesser in SRC group than TAS group, but not significantly (p=0.06). Operation time and X-ray exposure time were shorter in SRC group than in TAS group (all p<0.001). CONCLUSION: Both TAS and SRC could be selected as safe and effective treatment options for C1-2 instability. But the perioperative result, which is technical demanding and X-ray exposure might be expected better in SRC group compared to TAS group.

Safety Issues and Neurological Improvement following C1 C2 Fusion using C1 Lateral Mass and C2 Pedicle Screw in Atlantoaxial Instability

The evolution of instrumentation methods for C1 C2 fusion from the use of posterior wiring methods to transarticular screws and C1 lateral mass with C2 pedicle screw construct have improved fusion rates to almost 100%. However, the C1 lateral mass and C2 pedicle screw technique is technically demanding. This is a prospective review of a series of ten patients who was planned for C1 C2 fusion using C1 lateral mass and C2 pedicle screw technique between January 2007 and June 2009. The procedure was converted

Old Atlantoaxial Rotary Subluxation Associated with High-riding Vertebral Arteries: Arthrodesis Using C1 Lateral Mass Screws and C2 Laminar Screws: A Case Report

To the best of our knowledge, there has been no domestic report on posterior atlantoaxial fusion with segmental screw fixation using C2 laminar screws and C1 lateral mass screws for atlantoaxial subluxation. We report the result of this operation performed in a patient with old atlantoaxial rotary subluxation who required posterior fusion. We chose this technique in this patient because wire fixation was not suitable due to osteoporosis, and transarticular screw fixation and use of C2 pedicle screws were not feasible due to the peculiar bony anatomy of the axis.

Optimal Trajectories of C1 Lateral Mass Screws and C2 Pars-Pedicle Screws / 대한척추외과학회지

STUDY DESIGN: Surgical simulation using CT images of the cervical spine and computers. OBJECTIVES: The optimal trajectories for C1 lateral mass screws and C2 pars-pedicle screws were sought, and their accuracy evaluated. LITERATURE REVIEW SUMMARY: There have been a few suggestions for the trajectories of the screws listed above, but these are somewhat vague or impractical. MATERIALS AND METHODS: Using 1 mm-sliced CT scan images of 128 patients, and a V-works spine surgery simulator 4.0 (Cybermed, Inc., Korea), the optimal trajectories with which 4.0 mm screws can be inserted without breaching bone cortices were determined. The anatomical characteristics of the cases having a cortical perforation were analyzed. RESULTS: The insertion point suggested for a C1 screw was 1 mm lateral to the middle of the junction of the posterior arch and posterior inferior part of the lateral mass. The screw was directed 15 degrees medially and toward the junction of the superior 2/3 and inferior 1/3 of the anterior tubercle in the lateral fluoroscopic view. The C2 screw was directed 30 degrees medially, and toward the anterior end of the superior articular process, in the lateral fluoroscopic view. The insertion point was one where the screw was inserted close to the superomedial border of the pedicle. Using these trajectories, all (256/256) of the C1 screws were inserted safely. However, 6.3% (16/256) of the C2 screws breached the inferolateral cortices of the pedicles, due to the pedicles being either too narrow or too medially angulated. CONCLUSIONS: Herein, more practical and safe screw trajectories have been suggested. Using these trajectories, all the C1 and most of the C2 screws were able to be inserted safely. However, there were some cases in which the C2 screws could not be inserted without breaching the vertebral artery groove. Therefore, preoperative thin-slice CT scanning, with three-dimensional reconstruction and/or three-dimensional CT-angiography, is recommended for these cases.

Optimal Trajectories of C1 Lateral Mass Screws and C2 Pars-Pedicle Screws / 대한척추외과학회지

STUDY DESIGN: Surgical simulation using CT images of the cervical spine and computers. OBJECTIVES: The optimal trajectories for C1 lateral mass screws and C2 pars-pedicle screws were sought, and their accuracy evaluated. LITERATURE REVIEW SUMMARY: There have been a few suggestions for the trajectories of the screws listed above, but these are somewhat vague or impractical. MATERIALS AND METHODS: Using 1 mm-sliced CT scan images of 128 patients, and a V-works spine surgery simulator 4.0 (Cybermed, Inc., Korea), the optimal trajectories with which 4.0 mm screws can be inserted without breaching bone cortices were determined. The anatomical characteristics of the cases having a cortical perforation were analyzed. RESULTS: The insertion point suggested for a C1 screw was 1 mm lateral to the middle of the junction of the posterior arch and posterior inferior part of the lateral mass. The screw was directed 15 degrees medially and toward the junction of the superior 2/3 and inferior 1/3 of the anterior tubercle in the lateral fluoroscopic view. The C2 screw was directed 30 degrees medially, and toward the anterior end of the superior articular process, in the lateral fluoroscopic view. The insertion point was one where the screw was inserted close to the superomedial border of the pedicle. Using these trajectories, all (256/256) of the C1 screws were inserted safely. However, 6.3% (16/256) of the C2 screws breached the inferolateral cortices of the pedicles, due to the pedicles being either too narrow or too medially angulated. CONCLUSIONS: Herein, more practical and safe screw trajectories have been suggested. Using these trajectories, all the C1 and most of the C2 screws were able to be inserted safely. However, there were some cases in which the C2 screws could not be inserted without breaching the vertebral artery groove. Therefore, preoperative thin-slice CT scanning, with three-dimensional reconstruction and/or three-dimensional CT-angiography, is recommended for these cases.