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.

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.

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.

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.

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.

Computed tomography-based classification of axis vertebra: choice of screw placement.

PURPOSE: The purpose of the study was to: (1) introduce a new CT-based parameter: free facet area and provide its normative data; (2) standardize the method of measuring isthmus width and height of the axis vertebra; (3) propose a new grading system to predict the difficulty in inserting transarticular and C2 pedicle screws. METHODS: Spiral CT scans of 47 adult dry axis vertebrae were studied. The methods of measuring isthmus width, isthmus height and free facet area are described. RESULTS: The mean isthmus width was 5.04 mm on the right side and 5.42 mm on the left side. The mean isthmus height was 5.21 mm on the right side and 5.45 mm on the left side. Mean free facet area was 61.23 % on the right side and 70.18 % on the left side. A novel grading system is proposed on the basis of these three parameters. As per this grading system, 40.4 % of the sides were found to be difficult for transarticular and 24.5 % sides for C2 pedicle screw insertion (total score 2, 3, 4). A Management protocol is suggested on the basis of the grading system. CONCLUSION: Inserting a transarticular screw was more frequently difficult as compared to pedicle screw. A new CT-based parameter (free facet area) and an efficient grading have been proposed to help surgeons choose the appropriate screw options, appreciate the complex anatomy of this region and compare data across various studies.

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.

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.

Morphology of the transverse ligament of the atlas and the alar ligaments in the silver fox (Vulpes vulpes var).

BACKGROUND: Recent new anatomical and histological features of craniocervical junction in dogs and cats were described providing evidence of differences between the carnivore species. No information on these structures in foxes exists. RESULTS: Two parts of the alar ligaments were found. A longer one aroused from dens of axis to the internal (medial) surface of the occipital condyles and was called apical part. A shorter part originated from the entire length of the lateral edge of the dens of axis and terminated on the internal wall of the vertebral foramen of atlas and thus was called the lateral part. The transverse ligament of the atlas was widened in the mid region, above the dens of axis, and thickened at enthesis. Periosteal fibrocartilage was detected in the transverse ligament of the atlas at the enthesis, and sesamoid fibrocartilage was present on periphery in the middle of the ligament. CONCLUSIONS: The craniocervical junction in foxes differs in part from other carnivores such as dogs and cats but resembles that of mesaticephalic dogs. The sesamoid and periosteal fibrocartilage supports the transverse ligament of the atlas whereas the alar ligaments have no cartilage.

Atlantoaxial rotatory fixation--a cause of torticollis.

BACKGROUND: A rare, but important cause of torticollis in children is atlantoaxial rotatory fixation. If the patient remains undiagnosed for more than three months, surgery is generally the only therapeutic alternative. In this article we present our experiences of surgical treatment of late-diagnosed atlantoaxial rotatory fixation in children. MATERIAL AND METHOD: This article is based on a review of the case notes of patients who underwent surgery for atlantoaxial rotatory fixation in the Department for Neurosurgery at Oslo University Hospital, Rikshospitalet, during the period 2004-10. RESULTS: The material sample consists of six children aged from seven to 14 years. Five had suffered minor trauma to the upper neck region, while one had had an upper respiratory tract infection. The diagnosis was made 5-36 months after the onset of symptoms. In three of the patients, an attempt was made at closed reduction without success. A CT scan one year postoperatively showed a normal position of the atlantoaxial joint in two patients and partial reduction in three. In the sixth patient there was bone fusion at the time of the operation, and open reduction was unsuccessful. All six patients had reduced rotational movement of the neck at the one-year check-up. INTERPRETATION: All our patients were diagnosed more than five months after the onset of symptoms. Full or partial reduction was achieved in five of the six.

The anatomic and radiographic measurement of C2 lamina in Chinese population.

OBJECTIVE: In this study, we performed anatomic and computed tomography (CT) measurements of C2 lamina in Chinese people in order to provide the anatomic and radiographic data, and to verify the clinical applicability of trans-lamina screws to this population. METHODS: The anatomic and radiographic measurement was conducted on two separate groups, group A and group B. In group A, a total of 96 human adult (male 51, female 45) cadaver spines were included. The minimal height (H1), thickness (T), length (L1) of C2 lamina, height of the root of lamina (H2), distance from the entry point to the lateral rim of lamina (L2) and to the lateral rim of lateral mass (L3) were bilaterally measured using high precision calipers. The spino-laminar angles (angle A) were also included. In group B, a total of 112 volunteers (male 58, female 54) without upper cervical abnormality were enrolled. Angle A, H1, T, L1, H2, L2 and L3 were bilaterally measured using plain X-rays and reconstruction CT. All measurements were taken at the thinnest part of the lamina in the axial and coronal plane. RESULTS: All the measurements (except angle A) in males were significantly higher than those in females (P < 0.05). There was no significant difference in the values of bilateral laminae between group A and group B (P > 0.05). The thickness of 45% specimens was less than 6 mm. The length of lamina in all specimens was less than 2.5 cm, while only 5% of the specimens had a length of >3 cm from the entry point to the rim of lamina. The length from the entry point to the lateral rim of lateral mass was between 2.5 and 4.6 cm. In contrast, the length of only 5% specimens was longer than 4 cm. CONCLUSIONS: The preoperative radiographic evaluation is very important to determine the suitable size of screws. The diameter of screws is mainly restricted by the thickness of C2 lamina. It is safe to use screws with a length of 2.5-3.0 cm for Chinese people. The radiographic measurement method we used is simple, accurate and reliable for preoperative measurement.

Notes on the axial skeleton of the titanosaur Bonitasaura salgadoi (Dinosauria-Sauropoda).

Sauropod axial anatomy is particularly important in understanding morphological features and phylogenetic analyses. Spatial arrangement of zygapophyses and rib articulations, as well as their complex laminar development, help to recognize the relative position of isolated vertebral elements. The presence of anterior, mid and posterior elements along the cervical, dorsal and caudal series in Bonitasaura salgadoi allows the analysis of several anatomical characteristics. These include the pattern of neurocentral closure with unfused, partially fused and completely fused elements in a peculiar temporal sequence, as well as several neural spine modifications and the laminar arrangement. The variations in neural spine morphology include a lateral expansion of the distal tip in cervico-dorsal region, different lateral constituents of these lateral expansions, and a marked deviation in spine angulation. The spinal inclination allows the division into three easily recognizable vertebral regions separated by two landmarks, which adds support in the determination of an accurate vertebral position for isolated elements. Finally, an analysis of the vertebral laminae reveals the importance of examining vertebral series in order to recognize laminar homologies and developmental series. Two vertebral laminae are analyzed here.

Evaluation of anatomic landmarks and safe zones for screw placement in the atlas via the posterior arch.

Several studies have evaluated quantitative anatomic data for direct lateral mass screw fixation. To analyze anatomic landmarks and safe zones for optimal screw placement through the posterior arc of the human atlas, morphometric parameters of 41 adult native human atlas specimens were quantitatively measured. Internal dimensions of the atlas (lateral mass, maximum and minimum intraosseous screw length), minimum height and width of the posterior arc and optimal screw insertion angles were defined on pQCT scans. By this, an optimal posterior screw insertion point (OIP) and a preferable screw direction (PSD) through the posterior arch into the lateral mass of C1 were defined. External dimensions (transverse and sagittal diameter) as well as the width of the mid-portion of C1 lateral mass were significantly higher in male specimens. The mean height of the posterior arch at the vertebral artery groove was 4.1 +/- 0.8 mm in female and 4.6 +/- 0.9 mm in male specimens. The optimal screw insertion point was located 21.6 +/- 1.7 mm in female and 23.6 +/- 2.3 mm in male lateral from the posterior tubercle of C1 (P < 0.01). The preferable screw direction was a mean medial inclination of 7.9 +/- 1.9 degrees in female and 7.3 +/- 2.7 degrees in male specimens and a mean rostral direction of 2.4 +/- 1.8 degrees in female and 3.1 +/- 1.7 degrees in male specimens. In conclusion, the presented study provides information for the use and design of upper cervical spine instrumentation techniques, such as screw placement to C1 via the posterior arch. The characterization of working areas and safe zones (OIP, PSD) might contribute to a minimization of screw malposition in this highly demanding instrumentation technique.

Anatomical considerations for subaxial (C2) pedicle screw placement: a radiographic study with computed tomography in 93 patients.

STUDY DESIGN: Radiographic study. OBJECTIVE: More detailed anatomical knowledge of the C2 pedicle is required to optimize and minimize the risk of screw placement. The aim of this study was to evaluate the linear and angular dimensions of the true C2 pedicle using axial computed tomography. BACKGROUND DATA: Although earlier studies have analyzed the anatomy of the C2 pars interarticularis, little attention has been focused on the dimensions of the C2 pedicle. METHODS: Ninety-three patients (47 males, 46 females; mean age 48.4 y) who had previous cervical spinal computed tomography imaging were evaluated for this study. Axial images of the C2 pedicle were selected and the following pedicle parameters were determined: pedicle width (the mediolateral diameter of the pedicle isthmus, perpendicular to the pedicle axis) and pedicle transverse angle (PTA, ie, the angle between the pedicle axis and the midline of the vertebral body). RESULTS: The overall mean pedicle width was 5.8+/-1.2 mm. The mean pedicle width in male patients (6.0+/-1.3 mm) was greater than that in the female patients (5.6+/-1.1 mm). This difference was not found to be statistically significant (P=0.679). The overall mean PTA was 43.9+/-3.9 degrees. The mean PTA in male patients was 43.2+/-3.8 degrees, whereas that in female patients was 44.7+/-3.7 degrees. CONCLUSIONS: Given the significant variability in pedicle widths and the need for precise trajectory planning in pedicle cannulation, preoperative planning is absolutely mandatory. A significant percentage of patients have pedicle widths that may not accommodate screw fixation. In addition, the angle of entry into the C2 pedicle must be carefully measured for safe instrumentation at this level.

Preoperative radiographic factors and surgeon experience are associated with cortical breach of C2 pedicle screws.

STUDY DESIGN: A retrospective review study. OBJECTIVE: In this study, we attempt to identify radiographic variables associated with likelihood of intraoperative breach during C2 pedicle screw placement. In addition, we attempt to correlate surgeon experience with breach rate. SUMMARY OF BACKGROUND DATA: Pedicle screws have emerged as an effective approach for obtaining fixation of the axis, yet placement of C2 pedicle screws is technically demanding and poses the risk of injury to the vertebral artery. Given the evidence for substantial variation in C2 anatomy, preoperative assessment of computed tomography (CT) scans may indicate, which patients are at increased risk for cortical breach during the pedicle screw placement. MATERIALS AND METHODS: A retrospective review of all patients undergoing C2 pedicle screw fixation at a single institution over the last 6 years was conducted. Radiographic cortical breaches were defined on postoperative CT scans as visualization of the screw beyond the cortical edge. Radiographic measurements were determined from preoperative CT scans and were then correlated with breaches via Student t test. The association of breach rate with surgeon experience was evaluated using univariate linear regression. RESULTS: Ninety-three patients underwent placement of 170 screws. Cortical breach was detected on postoperative CT scans in 43 screws (25.3%). One clinically significant breach occurred with damage to the left vertebral artery intraoperatively. On axial CT sections, mean pedicle isthmus diameter was significantly smaller in patients with breach than in patients without breach for both left and right sides, P=0.006 and P=0.010, respectively. Specifically, a diameter of less than 6 mm was associated with a nearly 2-fold increase in risk of cortical breach (37% vs. 21%). Surgeons with greater experience in placing C2 pedicle screws were noted to have a lower breach incidence (P=0.004). CONCLUSIONS: During placement of C2 pedicle screws, likelihood of cortical breach may be associated with size of pedicle and surgeon experience. Extensive preoperative evaluation of CT scans and consideration of technical demands of procedure may help avoid complications with such internal fixation.

Variable morphology of the axis vertebrae in 100 specimens: implications for clinical palpation and diagnostic imaging.

OBJECTIVE: The purpose of this study was to investigate and measure the variable morphologies of axis vertebrae and explore the clinical significance of variations as it may pertain to clinical palpation and diagnostic imaging. METHODS: The common variable morphologies in 100 specimens of intact dry adult axis vertebrae (Chinese) were investigated and measured. The frequencies in deviation of odontoid processes, deviation of spinous processes, and presence of bifid spinous processes were observed. The distances between the apices of transverse processes and inferior articular facets were also measured. RESULTS: Variable morphologies of C2 that we observed were deviation of odontoid processes (14 cases, 14.0%), deviation of spinous processes (3 cases, 3.0%), and bifid spinous processes (95 cases, 95.0%). Of the bifid spinous processes, 56 had a process on the left side equal to the right side, 21 were longer on the left, and 18 were longer on the right. The distances between apices of transverse processes and inferior articular facets in the left side of C2 were 17.67 +/- 2.47 mm, and that of the right side were 17.81 +/- 2.55 mm. CONCLUSIONS: Because variable morphology of the axis is common, congenital deviation of the odontoid process, deviation of the spinous process, and asymmetrical bifid spinous processes should be taken into account during clinical palpation and diagnostic imaging.

Anatomic and radiological study on posterior pedicle screw fixation in the atlantoaxial vertebrae of children.

OBJECTIVE: To investigate the feasibility of posterior fixation with 3.5-mm pedicle screws in the atlantoaxial vertebrae of children. METHODS: In this study, atlantoaxial vertebrae specimens were obtained from 10 cadavers of children aged 6-8 years. We measured the height and width of the C(1) pedicle and the midportion of C(1) lateral mass; the width of C(1) posterior arch under the vertebral artery groove and the height of the external and internal one-third of this part; the external, internal height and the superior, middle, inferior width of the C(2) pedicle (transverse foramen). Furthermore, computed tomography (CT) axial scan was performed on 20 age-matched volunteers to obtain relative data of their atlantoaxial vertebrae. We measured the length and width of the C(1) and C(2) pedicles in the atlantoaxial cross-sectional plane. On CT workstation, we also measured the angles between the longitudinal axes of the atlantoaxial pedicles and the midsagittal plane. RESULTS: For the cadaveric specimen group, the height and width of the C1 pedicle were (5.26+/-0.44) mm and (6.26+/-0.75) mm respectively. The height of the medial one-third of the C1 posterior arch under the vertebral artery groove was (4.07+/-0.24) mm. The external, internal height and superior, middle, inferior width of the C2 pedicle was (6.86+/-0.48) mm, (6.67+/-0.49) mm, (6.63+/-0.61) mm, (5.41+/-0.39) mm and (3.71+/-0.30) mm, respectively. For the volunteer group measured by CT scan, the height and width of the C(1) pedicle were (5.47+/-0.34) mm and (6.63+/-0.54) mm respectively, while (6.59+/-0.51) mm and (5.13+/-0.42) mm of the C2 pedicle. The angles between the atlas, axis pedicles and the midsagittal plane were (9.60+/-1.32) degree and (27.80+/-2.22) degree respectively. CONCLUSION: It is feasible to place a 3.5-mm pedicle screw in the C(1) and C(2) pedicles of children aged 6-8 years old.

[Anatomical considerations for the placement of C2 spinous process screws].

OBJECTIVES: To quantitatively anatomically evaluate the C2 spinous process, analyze the anatomical feasibility of the C2 spinous process screws and its clinical significance. METHODS: To dissect and evaluate 30 cervical cadaveric spines of C2 which were taken to expose the lamina and spinous process. Anatomic quantitative evaluation of the C2 spinous process included its height and width. Twenty cervical cadaveric spines of C2 were chosen to the study of the placement of the C2 spinous process screws. The starting point for the C2 spinous process screw insertion was located at the base of the spinous process. After the entrance point of spinous process screws was determined, posterior C2 spinous process screw implantation was performed bilaterally under direct visualization. On the morphologic CT scan, the width of C2 spinous process base, the angle and length of the spinous process screw trajectory, and the distance between the tip of the screw and the spinal cord and the vertebral artery were measured. RESULTS: The average height and width of the C2 spinous process were (12.90 ± 1.30) mm and (18.86 ± 1.17) mm respectively. The C2 spinous process screws were successfully placed without impingement the spinal cord or the vertebral artery and the breakage of the spinous process. On the CT scan, the average width of the base of C2 spinous process was (20.7 ± 1.3) mm. The placed angles of the screws were 1.8° ± 1.0° in the axial plane. The distance between the tip of the screw and the spinal cord or the vertebral artery was (8.3 ± 2.6) mm and (20.2 ± 3.1) mm respectively. There were little differences between superior and inferior screws in the angle, the distance between the tip of the screw and the spinal cord or the vertebral artery, but without significance (P > 0.05). The average trajectory length of the C2 spinous process screws was (19.7 ± 1.1) mm. The average trajectory length of the superior spinous process screws was shorter than that of inferior spinous process screws, with great differences (t = 3.566, P < 0.01). CONCLUSIONS: There is the anatomic feasibility of the C2 spinous process screw fixation which may afford an alternative to standard screw placement for axis fixation. The biomechanical study for the C2 spinous process screw is also necessary.

A novel computer-assisted drill guide template for placement of C2 laminar screws.

The present method of C2 laminar screw placement relies on anatomical landmarks for screw placement. Placement of C2 laminar screws using drill template has not been described in the literature. The authors reported on their experience with placement of C2 laminar screws using a novel computer-assisted drill guide template in nine patients undergoing posterior occipito-cervical fusion. CT scan of C2 vertebrae was performed. 3D model of C2 vertebrae was reconstructed by software MIMICS 10.01. The 3D vertebral model was then exported in STL format, and opened in a workstation running software UG imageware12.0 for determining the optimal laminar screw size and orientation. A virtual navigational template was established according to the laminar anatomic trait. The physical vertebrae and navigational template were manufactured using rapid prototyping. The navigational template was sterilized and used intraoperative to assist the placement of laminar screw. Overall, 19 C2 laminar screws were placed and the accuracy of screw placement was confirmed with postoperative X-ray and CT scanning. There were not complications of related screws insertion. Average follow-up was 9 months (range 4-13 months), 77.8% of the patients exhibited improvement in their myelopathic symptoms; in 22.2% the symptoms were unchanged. Postoperative computed tomographic (CT) scanning was available for allowing the evaluation of placement of thirteen C2 laminar screws, all of which were in good position with no spinal canal violation. This study shows a patient-specific template technique that is easy to use, can simplify the surgical act and generates highly accurate C2 laminar screw placement. Advantages of this technology over traditional techniques include planning of the screw trajectory is done completely in the presurgical period as well as the ability to size the screw to the patient's anatomy.

Imaging anatomy and variation of vertebral artery and bone structure at craniocervical junction.

The objective of this article is to display the vertebral artery and bone structure at the craniocervical junction (CJVA and C(0-1-2)) with three-dimensional CT angiography (3DCTA) and identify their anatomic features and variations. Eighty-eight subjects without pathology of vertebral artery (VA) and C(0-1-2) were selected from head-neck CTA examination. 3D images were formed with volume rendering (VR) and multiplanar reconstruction (MPR). On the 3D images, CJVA and C(0-1-2) were measured, and their variations were observed. CJVA goes along C(0-1-2) with five curves, of which three curves are visibly away from C(0-1-2), one is 0.0-8.3 mm away at the second curve with 0.0-11.2 mm in width, another is 0.0-9.2 mm away at the fourth with 2.8-14.8 mm and the other is 0.0-6.2 mm away at the fifth. Statistical comparisons show that there is no significant difference in the measurements between left and right, and that the curves become smaller and farther away from C(0-1-2) with the increase of age. CJVA is not equal in size, with the biggest in the fourth curve and the smallest in the fifth. Statistical comparison shows the left CJVA is larger than the right in the fifth curve. Variations were found on CJVA in 16 cases and on C(1) in 12 cases. The anatomy and variations of CJVA and C(0-1-2) are complicated. It is of vital significance to identify their anatomic features in clinical practice.