Anatomical and computed tomographic analysis of C1 vertebra

Classifying vertebral artery anatomy abnormality in children with skeletal dysplasia

PURPOSE

Skeletal dysplasia (SKD) have predictably abnormal occipitocervical skeletal anatomy, but a similar understanding of their vertebral artery anatomy is not known. Knowledge and classification of vertebral artery anatomy in SKD patients is important for safe surgical planning. We aimed to determine if predictably abnormal vertebral artery anatomy exists in pediatric SKD.

METHODS

We performed a retrospective review of CTAs of the neck for pediatric patients at a single institution from 2006 to 2018. CTAs in SKD and controls were reviewed independently in blinded fashion by two radiologists who classified dominance, vessel curvature at C2, direction at C3, and presence of fenestration and intersegmental artery.

RESULTS

14 skeletal dysplasia patients were compared to 32 controls. The path of the vertebral artery at C2 foramen was no different between the cohorts or by side, right (p = 0.43) or left (p = 0.13), nor for medial or lateral exiting direction from C3 foramen on right (p = 0.82) or left (p = 0.60). Dominance was most commonly neutral in both groups (71% in SKD and 63% in controls). There were no fenestrated nor first intersegmental arteries in our cohort.

CONCLUSION

No systematic differences were detected between SKD and control patients with respect to vertebral artery anatomy. Nonetheless, surgically relevant variability was observed in both groups. Paying particular attention to the direction of exit at C3 and curvature at C2 with respect to the foramen and vessel dominance are important and easily classifiable abnormalities that both surgeons and radiologists can use to communicate and employ in pre-operative planning.

LEVEL OF EVIDENCE

III.

Location of the vertebral artery at C1 in children: how far out laterally can one safely dissect?

BACKGROUND

There is little information available on the anatomic location of the vertebral artery in pediatric patients undergoing a posterior cervical arthrodesis involving the first cervical vertebra (C1). The purpose of this study was to define how far laterally one can safely dissect posteriorly without risk to the vertebral artery in pediatric patients.

METHODS

A subset of computed tomography angiograms of the neck that had been previously obtained in patients at our institution was evaluated. The location of the vertebral artery was identified on both the right and the left side at the vertebral artery groove.

RESULTS

A total of 549 patients were included. The vertebral artery was an average of 13.97 mm (standard deviation, 1.89 mm) from the midline. Ninety-seven percent of the vertebral arteries were more than 1 cm lateral to the midline, and none were less than 8 mm from the midline. There was a significant difference among the age groups in the location of the vertebral artery, with the vertebral artery closer to the midline in younger patients (p < 0.001). In patients eight years of age or older, the average distance from the midline equaled the value reported for adults.

CONCLUSIONS

Patients under the age of eight years had vertebral arteries that were significantly closer to the midline compared with those of older patients; nonetheless, 97% of the vertebral arteries in the younger patients were more than 1 cm lateral to the midline.

CLINICAL RELEVANCE

Increased care must be taken when dissecting out laterally on C1 in younger patients, as the vertebral artery tends to be closer to the midline than has been described in adults.

Developmental morphology and ossification patterns of the C1 vertebra

BACKGROUND

The first cervical vertebra (C1) is a unique ring-shaped structure and is largely cartilaginous at birth. Our objectives were to retrospectively analyze the age of closure of the synchondroses and determine age-dependent morphological characteristics of the C1 vertebra using computed tomographic (CT) scans.

METHODS

Helical CT scans were made in fifty-four children as part of routine imaging of patients presenting to the emergency room with head injury, to exclude cervical spine trauma. Axial and sagittal reconstruction images of the C1 ring were analyzed for widths of the anterior and posterior synchondroses, outer and inner anteroposterior diameters, outer and inner transverse diameters, inner area of the spinal canal at C1, and heights of the anterior and posterior arches. Variations in these parameters were evaluated in age groups from infancy to eighteen years.

RESULTS

As ossification progressed, the widths of the anterior neurocentral and posterior synchondroses decreased with increasing age. Closure of the posterior synchondrosis was complete in all by thirty-six months, except in one fifty-five-month-old subject in whom the posterior synchondrosis was open. Closure of the anterior synchondrosis was generally found after thirty-six months. Growth of the mean outer and inner anteroposterior diameters, mean outer transverse diameter, and increase in canal area occurred with age up to the three to six-year group, following which measurements increased minimally or stayed relatively constant. The inner transverse diameter was largely unchanged from birth to maturity and appeared to be independent of age. Anterior and posterior ring heights showed a similar distribution, with an increase up to the nine to twelve-year age group, and relatively constant values thereafter.

CONCLUSIONS AND CLINICAL RELEVANCE

Data from this retrospective review of fifty-four CT scans of the cervical spine, weighted toward the youngest population, assist in understanding the age-dependent osseous anatomy and biomechanical stability of the C1 vertebra in the growing child, help to distinguish fractures from incomplete ossification, and help to formulate decisions on the use of internal fixation of C1 in the growing child.

Current issues with standards in the measurement and documentation of human skeletal anatomy

Digital modeling of human anatomy has become increasingly important and relies on well-documented quantitative anatomy literature. This type of documentation is common for the spine and pelvis; however, significant issues exist due to the lack of standardization in measurement and technique. Existing literature on quantitative anatomy for the spine and pelvis of white adults (aged 18-65 years, separated into decadal categories) was reviewed from the disciplines of anatomy, manipulative therapy, anthropometrics, occupational ergonomics, biomechanics and forensic science. The data were unified into a single normative model of the sub-axial spine. Two-dimensional orthographic drawings were produced from the 590 individual measurements identified, which informed the development of a 3D digital model. A similar review of full range of motion data was conducted as a meta-analysis and the results were applied to the existing model, providing an inter-connected, articulated digital spine. During these data analysis processes several inconsistencies were observed accompanied by an evidential lack of standardization with measurement and recording of data. These have been categorized as: anatomical terminology; scaling of measurements; measurement methodology, dimension and anatomical reference positions; global coordinate systems. There is inconsistency in anatomical terminology where independent researchers use the same terms to describe different aspects of anatomy or different terms for the same anatomy. Published standards exist for measurement methods of the human body regarding spatial interaction, anthropometric databases, automotive applications, clothing industries and for computer manikins, but none exists for skeletal anatomy. Presentation of measurements often lacks formal structure in clinical publications, seldom providing geometric reference points, therefore making digital reconstruction difficult. Published quantitative data does not follow existing international published standards relating to engineering drawing and visual communication. Large variations are also evident in standards or guidelines used for global coordinate systems across biomechanics, ergonomics, software systems and 3D software applications. This paper identifies where established good practice exists and suggests additional recommendations, informing an improved communication protocol, to assist reconstruction of skeletal anatomy using 3D digital modeling.

Cervical vertebra morphology in different skeletal classes. A three-dimensional computed tomography evaluation

OBJECTIVE

To describe cervical vertebra morphology in subjects with different anteroposterior jaw relationships.

MATERIALS AND METHODS

Cone-beam computed tomography images of 31 female subjects aged 19 to 41 years were evaluated. Subjects constituted two groups according to the ANB angle: group 1, skeletal Class II (ANB angle >5); and group 2, skeletal Class III (ANB angle <1). Nine linear measurements and one angular measurement were used to assess the vertebral morphology. The Mann-Whitney U-test was used for statistical analysis.

RESULTS

The mean atlas dorsal arch height was significantly shorter in Class II subjects compared with those in Class III (P < .05). The cervical vertebra morphological analysis by cone-beam computed tomography was of comparable precision to three-dimensional computed tomography evaluations. This study confirmed previous findings that Class II subjects have significantly lower atlas dorsal arch heights.

CONCLUSION

The height of the atlas dorsal arch of cervical vertebrae is affected by the anteroposterior skeletal pattern.

C1 lateral mass anatomy: Proper placement of lateral mass screws

STUDY DESIGN

Cadaveric specimens were measured to determine appropriate placement for C1 lateral mass screws. Instrumentation guidelines were developed and used to instrument a series of cadaveric specimens. Clinical experience with C1 lateral mass fixation was reviewed to evaluate results. Postoperative computed tomographic (CT) scans were reviewed to evaluate screw placement.

OBJECTIVES

The cadaveric study measured the dimensions of the atlas and determined ideal trajectory for screw placement. This technique was applied clinically, and 50 cases were retrospectively reviewed for fixation difficulties, neurologic or vascular injuries, and perioperative complications. Postoperative CT scans were reviewed when available.

SUMMARY OF BACKGROUND DATA

Halo application, posterior wiring, and C1 to C2 transarticular screws have been used to stabilize the upper cervical spine. Each technique has disadvantages, and C1 lateral mass fixation recently has gained popularity as a potential alternative. Recent anatomic studies have documented the dimensions of the C1 lateral mass and its ability to accommodate screw fixation. Small clinical series have documented early success with this technique.

METHODS

Fifteen specimens were stripped of soft tissue and measured by using calipers and CT scans. Guidelines were formulated for C1 lateral mass screw fixation. Additional specimens with intact soft tissue were instrumented without difficulty. A clinical series was reviewed to evaluate for complications related to this technique. Postoperative CT scans were reviewed to evaluate screw placement.

RESULTS

The C1 lateral mass safely accommodated screw fixation. Trajectory of 10 degrees medial and 22 degrees cephalad was preferred. The technique was safely applied in a series of 50 patients. Postoperative CT scans showed the ability of the surgeon to achieve the intended goals for starting point and safe trajectory.

CONCLUSIONS

C1 lateral mass fixation is a safe alternative for upper cervical fixation with several potential advantages versus other techniques, but further clinical evaluation is warranted.

Working area, safety zones, and angles of approach for posterior C-1 lateral mass screw placement: a quantitative anatomical and morphometric evaluation

Object

The authors measured relevant quantitative anatomical parameters to define safety zones for the placement of C-1 posterior screws.

Methods

Nineteen linear, two angular, and four surface parameters of 20 dried atlantal specimens were evaluated. The Optotrak 3020 system was used to define the working area. Ideal angles for screw positioning were measured using digital radiographs and a free image-processing program. Six silicone-injected cadaveric heads were dissected bilaterally to study related neurovascular anatomy.

The depth (range 5.2–9.4 mm, mean 7.2 ± 1.1 mm) and width (range 5.2–8.1 mm, mean 6.5 ± 0.9 mm) of the transverse foramen varied considerably among specimens. The mean posterior working area was 43.3 mm2. All specimens accommodated 3.5-mm-diameter screws, and 93% accepted 4-mm-diameter screws. In 10 specimens (50%), partial removal of the posterior arch was necessary to accommodate a 4-mm screw. The mean maximum angle of medialization was 16.7 ± 1.3°; the mean maximum superior angulation was 21.7 ± 4.7°.

Conclusions

The anatomical configuration of the atlas and vertebral artery (VA) varied considerably among the cadaveric specimens. The heights of the C-1 pedicle, posterior arch, and posterior lamina determine the posterior working area available for screw placement. The inferior insertion of the posterior arch may have to be drilled to increase this working area, but doing so risks injury to the VA. A dense venous plexus with multiple anastomoses may cover the screw entry site, potentially obscuring the operative view and increasing the risk of hemorrhage.

A new approach for the estimation of intervertebral disc volume using the Cavalieri principle and computed tomography images

This study was carried out to describe a simple, accurate and practical technique for estimating the volume of intervertebral disc (ID) by the combination of the Cavalieri principle and computed tomography (CT) images. Total eight lumbar IDs from two cadavers were CT scanned in axial, sagittal and coronal sections. The consecutive sections with 5 and 3mm thickness were used to estimate the volume of the IDs by the Cavalieri principle. Three investigators estimated the volume of IDs independently to evaluate inter-observer differences. When the results were compared to the real volumes of IDs measured by the fluid displacement technique, there was no significant difference between the real volume measurements and the Cavalieri estimation results of ID volumes (P > 0.05). Moreover, findings of three investigators did not show significant variations (P > 0.05). Our results indicate that the section thickness and the section planes did not affect the accuracy of the disc volume estimation. Thus the combination of CT scanning with the Cavalieri principle may be used as a direct and reliable technique to estimate the volume of IDs with a mean of 4 min workload per ID.