An exclusionary screening method based on 3D morphometric features to sort commingled atlases and axes.

In forensic commingled contexts, when the disarticulation occurs uniquely at the atlantoaxial joint, the correct match of atlas and axis may lead to the desirable assembly of the entire body. Notwithstanding the importance of this joint in such scenarios, no study has so far explored three-dimensional (3D) methodologies to match these two adjoining bones. In the present study, we investigated the potential of re-associating atlas and axis through 3D-3D superimposition by testing their articular surfaces congruency in terms of point-to-point distance (Root Mean Square, RMS). We analysed vertebrae either from the same individual (match) and from different individuals (mismatch). The RMS distance values were assessed for both groups (matches and mismatches) and a threshold value was determined to discriminate matches with a sensitivity of 100%. The atlas and the corresponding axis from 41 documented skeletons (18 males and 23 females), in addition to unpaired elements (the atlas or the axis) from 5 individuals, were superimposed, resulting in 41 matches and 1851 mismatches (joining and non-joining elements). No sex-related significant differences were found in matches and mismatches (p = 0.270 and p = 0.210, respectively), allowing to pool together the two sexes in each group. RMS values ranged between 0.41 to 0.77 mm for matches and between 0.37 and 2.18 mm for mismatches. Significant differences were found comparing the two groups (p < 0.001) and the highest RMS of matches (0.77 mm) was used as the discriminative value that provided a sensitivity of 100% and a specificity of 41%. In conclusion, the 3D-3D superimposition of the atlanto-axial articular facets cannot be considered as a re-association method per se, but rather as a screening one. However, further research on the validation of the 3D approach and on its application to other joints might provide clues to the complex topic of the reassociation of crucial adjoining bones.

Anatomy of the craniocervical junction - A review.

An in-depth understanding of the anatomy of the craniocervical junction (CCJ) is indispensable in skull base neurosurgery. In this paper, we discuss the osteology of the occipital bone, the atlas (C1) and axis (C2), the ligaments and the muscle anatomy of the CCJ region and their relationships with the vertebral artery. We will also discuss the trajectory of the vertebral artery and review the anatomy of the jugular foramen and lower cranial nerves (IX to XII). The most important surgical approaches to the CCJ, including the far lateral approach, the anterolateral approach of Bernard George and the endoscopic endonasal approach, will be discussed to review the surgical anatomy.

Two novel parameters to evaluate the influence of the age and gender on the anatomic relationship of the atlas and axis in children no more than 8 years old: imaging study.

PURPOSE: Because of the complex cervical vertebral embryology and some normal variations, the atlantoadental interval (ADI) was not suitable for the evaluation of the anatomic relationship between the atlas and axial in children less than 2 years old. And the influence of the age and gender on the anatomic relationship between atlas and axial in children was still unclear. Two novel parameters, atlas-axis anteroposterior distance (AAAD) and atlas-axis lateral distance (AALD), were invented to evaluate the anatomic relationship between the atlas and axis in the children no more than 8 years old with different age and gender. METHODS: Cross-sectional computed tomography (CT) scans of the atlantoaxial joint for 140 randomly selected pediatric patients no more than 8 years old were analyzed. On the ideal CT reconstruction images, AAAD, AALD, atlantoaxial lateral bending angle (AALB), and atlantoaxial rotation angle (AARA) were measured. RESULTS: There was no statistically significant difference between the mean AAAD in different age and gender groups. The 99% confidence interval for AAAD was 7.12-7.82 mm. There was no significant correlation between AAAD and AALB/AARA and AALD and AALB/AARA. CONCLUSION: The AAAD was less than 7.12 mm or much than 7.82 mm that suggested a possible instability in the atlantoaxial joint and could help the diagnosis of the atlantoaxial instability in children no more than 8 years old. There was no difference between the mean AAAD of pediatric patients no more than 8 years old in different age and gender groups.

Freehand C2 Pedicle Screw Placement: Surgical Anatomy and Operative Technique.

We present a surgical video demonstrating the anatomy and technique of freehand C2 pedicle screw placement using a cadaveric specimen and 3-dimensional simulation software. C2 pedicle screws have been shown to augment cervical constructs and provide increased biomechanical stability compared with pars screws due to the increased length and bony purchase of pedicle screws within the pedicle and vertebral body.1 The presence of vertebral artery variations within the transverse foramen may preclude pedicle screw placement, and these should be identified on preoperative imaging. The C2 pedicle can be directly palpated at the time of screw placement, which aids screw placement in cases of deformity or trauma. A freehand technique without the use of computed tomography scan guidance or intraoperative fluoroscopy decreases radiation exposure for the operator and patient and has been shown to be safe for patient-related outcomes.2-5 Complete exposure of the C2 posterior elements is key to identifying the pedicle. The trajectory is based on direct visualization of the medial and superior pedicle borders to avoid lateral or inferior breaches into the transverse foramen. A curved probe is used for access into the vertebral body, respecting the outer cortical walls of the pedicle. The intraosseous position is confirmed with a ball-tipped probe. Fluoroscopy should be performed after screw placement to confirm proper position. By accomplishing proper exposure and understanding the anatomy of the C2 pedicle, the placement of C2 pedicle screws using a freehand technique is a safe and efficient technique for high cervical fixation.

Internal Morphology of the Odontoid Process: Anatomic and Imaging Study with Application to C2 Fractures.

OBJECTIVE: Fracture of the odontoid process is a critical injury to diagnose and often treat. The aim of this anatomic study was to present a comprehensive understanding of this part of the C2 vertebra. METHODS: We used 20 C2 vertebrae. Samples underwent imaging (computed tomography [CT] with and without three-dimensional reconstruction, micro-CT, 1.5T magnetic resonance imaging) and sagittal and coronal sectioning using a bone saw. Sectioned specimens were imaged under a digital handheld microscope, and transillumination of the bone was used to highlight its internal trabecular pattern. Three samples underwent infusion of the odontoid process with a hardening substance and were then decalcified. RESULTS: Internal trabecular patterns of the odontoid process of all specimens were discernible. In sagittal and coronal sections, trabecular patterns were highlighted with transillumination, but the patterns were much clearer using the digital microscope. Magnetic resonance imaging and CT provided the least detail of the imaging methods, but the trabecular patterns could be identified. Three-dimensional reconstruction of CT data was the preferred imaging method over magnetic resonance imaging and CT without three-dimensional reconstruction. The most distinct trabecular and cortical patterns were seen using micro-CT. Osteoporosis was seen in 2 specimens (10%). Five specimens (25%) were found to have a subdental synchondrosis. For most specimens, the trabeculae were found throughout the odontoid process. CONCLUSIONS: Improved knowledge of the anatomy, structural composition, and variations within the C2 vertebra may allow for better treatment options and patient care.

Radiological and Surgical Anatomy of Ventral C1-C2 Complex.

AIM: To evaluate anatomical data of the bony structures during exploration of the C1-C2 complex. MATERIAL AND METHODS: This study included six formalin-fixed cadaveric head and neck specimens. Radiological images and anatomical measurements included: C1-C2 distance, bony distance between C1 anterior tubercle-nares and superior incisors, height of C1 anterior arch, and height and width of odontoid articular surface. RESULTS: The mean distance between C1 anterior tubercle-nares and superior incisors on maxilla were 96.16 ± 8.07 mm and 84.14 ± 9.16 mm, respectively. The mean height of C1 anterior arch was 13.89 mm. The meandistance between medial borders of right-left C1 lateral masses was 19.10 ± 1.80 mm. The mean distance between medial border of lateral midline on mass right and left sides were 9.43 ± 0.88 mm and 9.68 ± 0.97 mm, respectively. The mean height of C1 anterior arch at midline was 13.89 ± 2.48 mm, and the mean distance between ventral surface of anterior arch and ventral joint of odontoid at midline was 6.43 ± 1.29 mm. The anteroposterior, horizontal diameters of odontoid on its base were 12.12 ± 0.38 mm, and 11.12 ± 0.94 mm, respectively. The angles of transoral and transnasal approaches to C1 were 32.67 ± 4.59° and 32.00 ± 2.10°, respectively. CONCLUSION: A safe transoral or transnasal odontoidectomy requires accurate measurements and imaging regarding ventral C1-C2 relationships, distances of odontoid, lateral mass and midline.

Análisis morfométrico del axis para la fijación atlantoaxial / Morphometric analysis of the axis for atlantoaxial fixation

El objetivo de este estudio fue evaluar de manera integral los parámetros morfométricos de la vértebra axis (C2) en la población mexicana involucrados en la realización de procedimientos quirúrgicos con el fin de proveer datos cuantitativos indispensables en su abordaje quirúrgico. Para este estudio se utilizaron un total de 576 vértebras axis (C2) de población mexicana contemporánea. Las mediciones de las vértebras se efectuaron bilateralmente utilizando un vernier digital milimétrico con una precisión de 0.01 mm (Mitutoyo Digimatic w/Absolute Encoders- Series 500). Un total de 576 vértebras axis (C2), fueron medidas de manera bilateral, todas nuestras mediciones se reportaron en mm. El promedio del ancho del pedículo fue de 8,96 mm con una DE ± 2,11 mm. El promedio de la altura del pedículo fue de 10,82 mm con una DE de ± 1,89 mm. El promedio de la altura del proceso odontoideo fue de 16,90 mm con una DE de ± 2,99 mm. El promedio del ancho del proceso odontoideo fue de 9,99 mm con una de DE de ± 0,80 mm. El promedio del diámetro de la faceta articular fue de 8,44 mm con una DE de ± 1,04 mm. El promedio del diámetro AP del cuerpo vertebral fue de 15,11 mm con una DE de ± 1,88 mm. El promedio del diámetro trasverso del cuerpo vertebral fue de 17,93 mm con una DE de ± 2,22 mm. El promedio de la altura del cuerpo vertebral fue de 18,54 mm con una DE de 2,38 mm. El promedio de la altura de las láminas fue de 11,53 mm con una DE de ± 1,39 mm. El promedio del ancho de las láminas fue de 6,10 mm con una DE de ± 1,44 mm. Los resultados obtenidos en nuestras mediciones demuestran una variación con los resultados de otros autores en diferentes estudios de piezas osteológicas y de estudios de imagen del axis (C2), lo que sugiere, con el fin de reducir los riesgo de daño a estructuras neurovasculares, utilizar técnicas y medidas especiales para la estabilización atlantoaxial de la población mexicana.

The aim of the study was to evaluate the morphometric parameters of the axis vértebra (C2) in the Mexican population involved in the performance of surgical procedures in order to provide essential quantitative data in their surgical approach. A total of 576 axis vertebrae (C2) of contemporary Mexican population were used for this study. The measurements of the vertebrae were made bilaterally using a millimeter digital vernier with an accuracy of 0.01 millimeters (Mitutoyo Digimatic w / Absolute Encoders - Series 500). A total of 576 axis vertebrae (C2) were measured bilaterally, all our measurements were reported in millimeters. The average width of the pedicle was 8.96 mm with a SD ± 2.11 mm. The average height of the pedicle was 10.82 mm with a SD of ± 1.89 mm. The average height of the odontoid process was 16.90 mm with a SD of ± 2.99 mm. The average width of the odontoid process was 9.99 mm with a SD of ± 0.80 mm. The average diameter of the articular facet was 8.44 mm with a SD of ± 1.04 mm. The average diameter of the AP of the vertebral body was 15.11 mm with a SD of ± 1.88 mm. The average transverse diameter of the vertebral body was 17.93 mm with a SD of ± 2.22 mm. The average height of the vertebral body was 18.54 mm with a SD of 2.38 mm. The average height of the lamina was 11.53 mm with a SD of ± 1.39 mm. The average width of the lamina was 6.10 mm with a SD of ± 1.44 mm. The results obtained in our measurements show a variation with the results of other authors in different studies of osteological pieces and studies of the axis image (C2), which suggests the use of techniques and special measures for the atlantoaxial stabilization of the Mexican population in order to reduce the risk of damage to neurovascular structures.

Proposal of a New Safety Margin for Placement of C2 Pedicle Screws on Computed Tomography Angiography.

BACKGROUND: Screw diameters currently available are based on the literature available. No data are available for the safety margin available for C2 pedicle screw placement. The objective of this study was to define the average pedicle size available for placing C2 pedicle screws and to quantify the safety margin available in case of lateral breach of screw. METHODS: Computed tomography angiograms of 259 patients (161 men, 98 women) were analyzed to calculate the C2 pedicle width, the area of the transverse foramen (TF) and the vertebral artery (VA), and the occupation ratio (OR) of the VA within the TF. The VA was classified into groups based on its lie within the TF (anteromedial, anterolateral, posteromedial, posterolateral, central, ectatic). The distance which the pedicle screw can breach without encountering the VA was calculated (lateral pedicle to vertebral artery distance [LPVA]). The diameters of the VA and the TF were estimated, and their difference gives the safety margin in case of breach of the lateral cortex of the C2 pedicle. RESULTS: The mean mediolateral diameter of the pedicle isthmus, perpendicular to the pedicle axis, in women was 5.3 mm and in men it was 5.8 mm. This difference was statistically significant. In 53.9% (122/226) of patients, the VA was dominant on the left side. The overall mean OR at the C2 vertebral level was found to be 37.3%. The mean LPVA was 0.9 mm, and the average overall safety margin available was 2.5 mm (range, 0.4-5.3 mm). CONCLUSIONS: This study describes the relationship of the VA in the C2 TF and the relative risk during pedicle screw fixation.

Anatomic Study of Nutrient Foramina of Posterior Axis with Application to C2 Pedicle Screw Placement.

OBJECTIVE: Pedicle screws placed into C2 necessitate a thorough understanding of this bone's unique anatomy. Although multiple landmarks and measurements have been used by surgeons, these are often varied in the literature with no consensus. Herein, we studied one recently proposed landmark using the nutrient foramina of the posterior aspect of C2 for pedicle screw placement. METHODS: On 19 (38 sides) C2 dry bone specimens, the presence, size, location, and distance from the midline of the nutrient foramina found at the junction between the isthmus and lamina were documented and measured. In addition, to discern the source of the artery entering such foramina, an injected adult cadaver was dissected. RESULTS: The number of foramina ranged from 0-5 with a mean of 1.84. On 3 sides, no foramina were identified. The mean diameter of the foramina was 0.57 mm. The location of the foramina was at position 1 on 9.5% of sides, position 2 on 66.4% of sides, and position 3 on 24.1% of sides. The mean horizontal distance from the midline of the spinous process of C2 to the foramina was 25.17 mm. In the cadaveric specimen, the source of the artery entering these C2 nutrient foramina was found to be distal branches of the deep cervical artery. CONCLUSIONS: We found the nutrient foramina of the C2 laminae are useful for pedicle screw placement. However, there are minor variations of the number and position of these structures. Lastly, on the basis of our study, 7.9% (n = 3) of sides will not have such foramina.

Trabecular Anatomy of the Axis Vertebra: A Study of Shaded Volume-Rendered Computed Tomography Images.

BACKGROUND: To date, trabecular morphology studies have been conducted on thin-section computed tomography (CT) scans of cadaveric bone. Here we describe the trabecular anatomy of the axis vertebra as revealed by an innovative imaging tool. METHODS: Ten patients who underwent thin-slice CT scans for suspected cervical spine injury were prospectively subjected to shaded volume-rendered 3-dimensional reconstruction of the images. The trabecular anatomy thus depicted was recreated, and the mechanical vectors were deduced independently by a senior radiologist and spine surgeon and then matched. The clinical implications were postulated. RESULTS: The most striking trabeculae are the vertical compression trabeculae connecting the C1 facet to the C3 body. The center of the body of C2 has a space with sparse trabeculae; similarly, the pars interarticularis also has a clear void. The dens contain predominantly tensile trabeculae that are retained even in older patients. Midline remnants of the odontoid body synchondrosis persist even into late adulthood. CONCLUSIONS: Shaded volume-rendered imaging appears to be an excellent tool for studying the trabecular anatomy of cancellous bone. The weight-bearing trabeculae run from the C1-2 facet to the C3 body; the inferior facet contributes little to weight-bearing.

A Novel C2 Screw Trajectory: Preliminary Anatomic Feasibility and Biomechanical Comparison.

BACKGROUND: Pedicle screw and translaminar screw fixation in C2 may not be applicable in many patients with anatomic abnormalities or narrow laminar thickness and spinous process height. The aim of this study was to assess morphometric and mechanical feasibilities of a novel alternative screw trajectory that pierces the bifid base of C2. METHODS: Anatomic measurements that determined the feasibility of spinous process bifid base (SPB) screw fixation were assessed in 14 cadaveric C2 vertebrae. Pullout tests to assess ultimate fixation strength for 3 screw trajectories (transpedicular, translaminar, and SPB) were performed in cadaveric vertebrae for comparison. RESULTS: Anatomic measurements included mean spinous process height (10.4 ± 4.2 mm) and mean bilateral bifid base length (10.1 ± 2.2 mm) and thickness (left, 4.4 ± 1.0 mm; right, 4.3 ± 0.9 mm). In 64% (9/14) of specimens, bifid base length was ≥9 mm. Mean pullout strength for transpedicle, translaminar, and SPB screws in 9 viable specimens was 648 ± 305 N, 628 ± 417 N, and 755 ± 279 N. CONCLUSIONS: SPB screw fixation may be viable anatomically and mechanically for C2 fixation. Feasibility of SPB screw fixation is determined by length, thickness, and mutual angle of the bilateral bifid bases. Patients with thin (<4 mm) and short (<9 mm) bifid bases are not likely to be suitable candidates. SPB screw fixation shows potential as an alternative approach or a salvage technique for patients with high-riding vertebral arteries or severely thin C2 lamina and warrants further investigation.

Anatomical considerations of C2 lamina for the placement of translaminar screw: a review of the literature.

PURPOSE: The thorough knowledge of C2 lamina anatomy is essential for the avoidance of complications during screw fixation. We performed a review of the literature, aiming to detect what was found about anatomical feasibility of C2 translaminar fixation in different populations, along with possible recommendations for the avoidance of complications, and to detect whether factors such as race or gender could influence axis lamina anatomy and fixation feasibility. METHODS: We performed a search in PubMed and Cochrane database of systematic reviews for studies which correlated axis lamina anatomy with fixation feasibility. We extracted data concerning measurements on C2 lamina, the methods and conclusions of the studies. RESULTS: Twenty-six studies met our inclusion criteria. The studies mainly focused on Asian populations. Male gender was generally related to larger anatomical parameters of C2 lamina. The use of a C2 translaminar screw with a diameter of 3.5 mm was generally feasible, even in children, but there was disagreement about risk of vertebral artery injury. Computed tomography was most frequently recommended preoperatively. Three-dimensional reconstruction was suggested by some authors. CONCLUSION: C2 lamina anatomy generally permitted screw fixation in most studies, but there was disagreement about risk of vertebral artery injury. Preoperative computed tomography was generally recommended, while, according to some authors, three-dimensional reconstruction could be essential. However, there is a relative lack of studies about non-Asian populations. More research could further illustrate the anatomy of C2 lamina, clarify the safety of axis fixation for more populations and perhaps modify preoperative imaging protocols.

Anatomic Study of Anterior Transdiscal Axial Screw Fixation for Subaxial Cervical Spine Injuries.

Anterior transdiscal axial screw (ATAS) fixation is an alternative or supplement to the plate and screw constructs for the upper cervical spine injury. However, no existing literatures clarified the anatomic feasibility of this technique for subaxial cervical spine. Therefore, the objective of this study was to evaluate the anatomical feasibility and to establish guidelines for the use of the ATAS fixation for the subaxial cervical spine injury.Fifty normal cervical spines had radiographs to determine the proposed screw trajectory (the screw length and insertion angle) and the interbody graft-related parameters (the disc height and depth, and the distance between anterior vertebral margin and the screw) for all levels of the subaxial cervical spine. Following screw insertion in 8 preserved human cadaver specimens, surgical simulation and dissection verified the feasibility and safety of the ATAS fixation.Radiographic measurements showed the mean axial screw length and cephalic incline angle of all levels were 41.2 mm and 25.2°, respectively. The suitable depth of the interbody graft was >11.7 mm (the distance between anterior vertebral margin and the screw), but <17.1 mm (disc depth). Except the axial screw length, increase in all the measurements was seen with level up to C5-C6 segment. Simulated procedure in the preserved specimens demonstrated that ATAS fixation could be successfully performed at C2-C3, C3-C4, C4-C5, and C5-C6 levels, but impossible at C6-C7 due to the obstacle of the sternum. All screws were placed accurately. None of the screws penetrated into the spinal canal and caused fractures determined by dissecting the specimens.The anterior transdiscal axial screw fixation, as an alternative or supplementary instrumentation for subaxial cervical spine injuries, is feasible and safe with meticulous surgical planning.

Medially-shifted rather than high-riding vertebral arteries preclude safe pedicle screw insertion.

We enrolled 100 patients who underwent preoperative CT angiography before cervical spine instrumentation and investigated the morphology of the C2 pedicle from the perspective of pedicle screw (PS) trajectory using volume rendering and multiplanar reconstruction. The narrowest portion of the pedicle was identified as the pedicle isthmus. Safe C2 PS insertion was regarded to be not feasible when the height of the medullary cavity of the pedicle isthmus and/or width of the medullary cavity of the pedicle isthmus was ⩽4mm. Forty-five (22.5%) pedicles were ⩽4mm in width, and safe insertion of a PS was determined to be not feasible. Among these, seven pedicles were ⩽4mm in both height and width. The remaining 38 pedicles were ⩽4mm in width with heights >4mm. There was no pedicle with a width >4mm and height <4mm. In other words, short pedicles were always concomitantly narrow. Therefore, the seven pedicles ⩽4mm in both height and width were considered to be morphologically narrow. The heights of the pedicle isthmus were not limited by the vertebral artery groove (VAG) and safe C2 PS insertion can be considered feasible where the VAG is marginally cranial, whereas the widths of the pedicle isthmus are limited by the VAG. Therefore, safe C2 PS insertion is precluded only when the VAG courses cranially and medially. It is a medially-shifted, rather than a high-riding, vertebral artery that precludes safe C2 PS insertion. Therefore to avoid vertebral artery injury an axial CT scan, parallel to the pedicle axis, should be evaluated before C2 PS insertion.

Morphometric analysis of cervical vertebrae in relation to mandibular growth.

INTRODUCTION: Cervical vertebral maturation (CVM) methods have been criticized because of their subjective nature. The aims of this study were (1) to analyze the morphometric changes in the outline of the second to fourth cervical vertebrae with growth and (2) to test the validity of the CVM method for determining the mandibular growth peak. METHODS: Lateral cephalograms of 25 participants from ages 10 to 16 years were acquired from the Burlington Growth Study, and the CVM stage was qualitatively determined. Mandibular and cervical vertebral semilandmarks were then digitized, and point distribution models were used to describe the morphometric templates of the vertebrae in relation to chronologic age and the timing of peak mandibular growth. Mixed model analysis was used to determine the relationship between mandibular length, sex, CVM stage, and chronologic age. RESULTS: Morphometric changes of the second to fourth cervical vertebrae during growth were consistent with the CVM descriptions. However, mandibular length changes were not significantly associated with CVM stages after adjusting for chronologic age. Morphometric templates of vertebral shapes before and during the mandibular growth peak were similar, with changes detectable only after the growth peak had passed. Morphometric vertebral shape changes varied between the sexes. CONCLUSIONS: Morphometric changes of the cervical vertebrae and the CVM method could not accurately identify the mandibular growth peak.

Does the Pharyngeal Airway Recover After Sagittal Split Ramus Osteotomy for Mandibular Prognathism?

PURPOSE: Mandibular setback surgery can adversely affect the pharyngeal airway. The aim of this study was to investigate changes of the pharyngeal airway at specific intervals during a 12-month period after bilateral sagittal split ramus osteotomy (BSSO) for correction of mandibular prognathism. MATERIALS AND METHODS: This retrospective cohort study included patients with mandibular prognathism who underwent BSSO. The pharyngeal airway was measured at 3 different levels on lateral cephalograms: the uvula tip, the most inferior-anterior point on the body of the second cervical vertebra (low-C II), and a midanterior point on the body of the third cervical vertebra (mid-C III). The pharyngeal airway was measured preoperatively, immediately postoperatively, and 1, 3, 6, and 12 months postoperatively. The measurements at each level were compared. Multivariable analysis of variance was used to measure the changes in pharyngeal airway space over time. RESULTS: The study sample was composed of 30 patients (14 men and 16 women) who were diagnosed with mandibular prognathism. The pharyngeal airway at the uvular tip level was significantly reduced by 39% (P < .001) after surgery and was significantly improved by 26% (P < .01) from baseline at 1 month postoperatively. The pharyngeal airway at the low-C II level was significantly reduced by 27% (P < .001) after surgery and was significantly improved by 24% (P < .01) from baseline at 1 month postoperatively. The pharyngeal airway at the mid-C III level was significantly reduced by 23% (P < .001) after surgery and was improved by only 13% from baseline at 1 month postoperatively. Additional statistical changes were not noted on 3 and 6 months postoperative radiographs at all levels. The pharyngeal airway was decreased by 16, 19, and 8% from baseline at 12 months postoperatively, respectively. The upper airway length was significantly increased immediately after surgery (P < .001), but was incompletely recovered at 12 months postoperatively. CONCLUSION: The outcomes of this study indicate that the pharyngeal airway gradually recovers over time. An immediate postoperative reduction in pharyngeal airway space can induce or exacerbate obstructive sleep apnea symptoms; thus, any pre-existing symptoms should be screened and considered for surgical treatment planning.

[ANATOMIC STUDY ON ENTRY POINT AND IMPLANT TECHNIQUE FOR C2 PEDICLE SCREW FIXATION].

OBJECTIVE: To determine the entry point and screw implant technique in posterior pedicle screw fixation by anatomical measurement of adult dry samples of the axis so as to provide a accurate anatomic foundation for clinical application. METHODS: A total of 60 dry adult axis specimens were selected for pedicle screws fixation. The entry point was 1-2 mm lateral to the crossing point of two lines: a vertical line through the midpoint of distance from the junction of pedicle medial and lateral border to lateral mass, and a horizontal line through the junction between the lateral border of inferior articular process and the posterior branch of transverse process. The pedicle screw was inserted at the entry point. The measurement of the anatomic parameters included the height and width of pedicle, the maximum length of the screw path, the minimum distance from screw path to spinal canal and transverse foramen, and the angle of pedicle screw. The data above were provided to determine the surgical feasibility and screw safety. RESULTS: The width of upper, middle, and lower parts of the pedicle was (7.35 ± 0.89), (5.50 ± 1.48), and (3.97 ± 1.01) mm respectively. The pedicle height was (9.94 ± 1.16) mm and maximum length of the screw path was (25.91 ± 1.15) mm. The angle between pedicle screw and coronal plane was (26.95 ± 1.88) degrees and the angle between pedicle screw and transverse plane was (22.81 ± 1.61) degrees. The minimum distance from screw path to spinal canal and transverse foramen was (2.72 ± 0.83) mm and (1.98 ± 0.26) mm respectively. CONCLUSION: According to the anatomic research, a safe entry point for C2 pedicle screw fixation is determined according to the midpoint of distance from the junction of pedicle medial and lateral border to lateral mass, as well as the junction between the lateral border of inferior articular process and the posterior branch of transverse process, which is confirmed to be effectively and safely performed using the entry point and screw angle of the present study.

Appropriate size and angulation for axis screw placement.

BACKGROUND: A screw larger than 4.0-4.5-mm-diameter screw has now become the preferred sizefor providing maximum anchorage during atlantoaxial segmental fixation and transarticular screw fixation. At present, there are no studies available of Axis (C2) morphology related to screw placement specifically in Thai patients, a situation that might result in surgical complications. OBJECTIVE: The purpose ofthis study was to determine the typical width, height and angulations in both C2 pars interarticularis and C2 pedicle in Thai population. MATERIAL AND METHOD: A radiographic-based study was conducted in 54 Thai patients aged over 20 from July 2011 to January 2012 in Chiang Mai University Hospital. C2 parameters including the height, width, medial angulation and superior angulation of the pars interarticularis and the pedicle were measured by using a CT scan. Allparameters were measured using the ONIS 2.3 program. RESULTS: The C2 pedicle in Thais was found to have a mean width of 5.47 mm (range 3.28-6.81 mm), a height 7.54 mm (5.9-9.54), a superior angulation of 27.54° (range 20. 65°-33.95°), and a medial angulation of 38.95° (range 28.07°-52.85°). C2 Pars interarticularis had a mean width of 7.72 mm (range 5.93-10.61 mm), a height of 4.47 mm (range 2.33-6.3 mm), a superior angulation of 49.85° (range 41.89°-58.65°), and a medial angulation of 6.76° (range 1.18°-13.5°). CONCLUSION: Because the mean height of pars interarticularis is 4.47 mm, atlantoaxial arthrodesis should not use 4.5-mm-diameter screw, especially transarticular screws, due to the possibility of vascular and nerve damage.

A statistical shape model of the human second cervical vertebra.

PURPOSE: Statistical shape and appearance models play an important role in reducing the segmentation processing time of a vertebra and in improving results for 3D model development. Here, we describe the different steps in generating a statistical shape model (SSM) of the second cervical vertebra (C2) and provide the shape model for general use by the scientific community. The main difficulties in its construction are the morphological complexity of the C2 and its variability in the population. METHODS: The input dataset is composed of manually segmented anonymized patient computerized tomography (CT) scans. The alignment of the different datasets is done with the procrustes alignment on surface models, and then, the registration is cast as a model-fitting problem using a Gaussian process. A principal component analysis (PCA)-based model is generated which includes the variability of the C2. RESULTS: The SSM was generated using 92 CT scans. The resulting SSM was evaluated for specificity, compactness and generalization ability. The SSM of the C2 is freely available to the scientific community in Slicer (an open source software for image analysis and scientific visualization) with a module created to visualize the SSM using Statismo, a framework for statistical shape modeling. CONCLUSION: The SSM of the vertebra allows the shape variability of the C2 to be represented. Moreover, the SSM will enable semi-automatic segmentation and 3D model generation of the vertebra, which would greatly benefit surgery planning.

Pedicle axis view combined by sacral mapping can decrease fluoroscopic shot count in percutaneous iliosacral screw placement.

BACKGROUND: Percutaneous iliosacral screw fixation of the posterior pelvic ring is a demanding procedure with high exposure to radiation. The conventional technique includes the use of three classical projections with the C-arm: inlet, outlet, and true lateral views. A projection in the axis of the upper sacral alar pedicles with a 30° cephalad and 30° ventral oblique view would help in obtaining a more accurate visualization of the safe corridor. Two subcutaneously placed K-wires, one placed horizontally and one vertically, may facilitate the starting point and aim changes by offering the surgeon an option for exactly matching the position of the sacrum with the image. The purpose of this study was to detect if the radiation application could be decreased by our new methodology. METHODS: Seventeen patients with pelvic posterior ring disruptions, in which percutaneous iliosacral screw placement was indicated, were included in the study. Group 1 comprised 7 patients in whom conventional projections and technique were used. Group 2 comprised 10 patients in whom 30°­30° projection and sacral mapping technique via two subcutaneous K-wires were applied. Radiation exposure time, total fluoroscopic shot count, fluoroscopic shot count needed for only guide wire and screw placement, radiation dose, and complications were compared between the two groups. RESULTS: The median number of fluoroscopic images for guide and screw placement was 132 (56­220) and 29.5 (19­83) in Groups 1 and 2, respectively, and the difference was statistically significant (p < 0.001). The median total fluoroscopic radiation time was 138 (68­234) and 52 (28­77) s in Groups 1 and 2, respectively, and the difference was significant (p < 0.001). Group 1 had a significantly higher median radiation dose than Group 2 [3020 (1502­6032) vs. 1192 (426­2359); (p = 0.001)]. CONCLUSIONS: Iliosacral screw placement with the help of sacral mapping and a fourth view, "30°­30°", helps the surgeon to markedly reduce the fluoroscopic shots, radiation time and dose during guide wire and screw placement. LEVEL OF EVIDENCE: Therapeutic, Level II.