Clival Screw Placement in Patient with atlas assimilation: A CT-based feasibility study

Morphological Evaluation of the Subaxial Cervical Spine in Patients with Basilar Invagination: A CT-based Study

STUDY DESIGN

Retrospective study.

OBJECTIVE

To evaluate the morphologic features of the subaixal cervical spine in patients with basilar invagination (BI) and provide information for the accurate screw placement in this region.

SUMMARY OF BACKGROUND DATA

BI is a congenital anomaly, comprising a wide range of abnormal structures. The screw fixation can be required in situation that BI is combined with subaxial cervical spine pathologies. However, there are no literatures specifically addressed the subaxial cervical morphology of BI.

METHOD

A total of 42 BI patients were included in this retrospective study. Forty-two patients without head or cervical disease were matched for sexes and ages. Information on radiographic features of the subaxial cervical spine was collected and compared systematically.

RESULTS

There were no differences in the age and sex between the BI and control group. The BI group manifested a wider pedicle and laminar than the control group at all cervical levels, except for the pedicle of C6 and C7, and the laminar of C3 and C6. In addition, the BI group had a wider lateral mass from C3 to C5 than the control group. There were no differences in most measurements of the length of pedicle, laminar, and lateral mass.

CONCLUSION

BI patients have a wider pedicle and laminar than the general population in the subaxial cervical spine, but the same size in length of pedicle, laminar, and lateral mass.Level of Evidence: 4.

The Feasibility of Anterior Occipital Condyle Screw for the Reconstruction of Craniovertebral Junction: A Digital Anatomical and Cadaveric Study of a Novel Technique

Background

Anterior occipital condyle screw (AOCS) could be a feasible alternative technique for occipitocervical fusion for reconstruction of craniovertebral junction. This study aimed to analyze the feasibility of AOCS.

Methods

The craniovertebral junction computed tomography (CT) scans of 40 adults were enrolled and imported into Mimics software. Then, the three-dimensional reconstruction digital model of craniovertebral junction was established to determine entry point, insertion angle, and screw’s trajectory. After AOCS insertion into ten human cadaver spine specimens, CT scans were performed to verify the location between screws and important structures.

Results

The optimal entry point was located caudally and medial to the ventral of occipital condyle. The optimal trajectory was in inclination angle (5.9°±3.4°) in the sagittal plane and divergence angle (26.7°±6.0°) in the axial plane with the screw length around 21.6±1.2mm. None of the screws invaded the hypoglossal canal and vertebral artery in any of the specimens.

Conclusion

AOCS fixation is a feasible, novel technique for anterior craniovertebral junction reconstruction, and it could be an effective alternative operation for anterior reconstruction with titanium mesh cage.

Anatomical analysis of the occipital bone in patients with basilar invagination: a computed tomography-based study

BACKGROUND CONTEXT

The occipital bone is often involved in the surgical treatment of basilar invagination (BI). However, the anatomy of the occipital bone associated with BI patients has yet to be investigated.

PURPOSE

To present a morphological map of the occipital bone in BI patients and help guide screw placement for occipitocervical fusion.

STUDY DESIGN

A retrospective case-control study.

METHODS

Radiological measurements of the occipital bone were performed on computed tomography images based on a matrix of 99 points centered around the external occipital protuberance (EOP) in a cohort of 50 BI patients and 50 cases with no head and cervical disease. The comparison between the BI group and the control group was assessed using Student t analysis and p<.05 was considered statistically significant.

RESULTS

All thicknesses measured from points of the matrix in the BI group were thinner than those in the control group (p<.05). The maximum thicknesses in both groups were located at the center of the EOP, which were 15.11±2.84 mm in the BI group and 17.56±3.03 mm in the control group, respectively. Additionally, thickness decreased with the distance away from the center of EOP.

CONCLUSIONS

The occipital bone in BI patients is thinner than that in the general population. A limited safe zone in BI patients is available for surgeons to place screws, which may need to be fully evaluated before operation.

Clival screw and plate fixation by the transoral approach for the craniovertebral junction: a CT-based feasibility study

PURPOSE

A clivus screw and plate was invented and proved to strengthen the stability of the craniovertebral junction (CVJ). However, it is unclear whether the clivus screw and plate could be placed onto the CVJ by transoral approach. Therefore, the present study aims to evaluate the feasibility of clivus screw and plate placement by transoral approach and investigate its relative anatomic parameters.

METHODS

A total of 80 normal adults (40 males/40 females) with an average age of 60.4 ± 11.6 years old were enrolled in this study. All parameters were measured in a supposed maximums mouth-opening status on computed tomography images, where the vertex of lower incisor was defined as Point A. The vertical intersection from Point A to extracranial clivus was defined as Point B, and its distance to the bottom of clivus was measured as B length. Point B was considered as ideal screw entry point. All the cases were divided into three types based on the location of Point B: above the top portion (Type 1), between the top and bottom portion (Type 2), and below the bottom portion (Type 3) of extracranial clivus. The B Length was defined as a minus value if the case belonged to Type 3. The anterior skull base angle, the angles between tangent of extracranial clivus and the lines from Point A to different parts of clivus, and distances between Point A and clivus and C1-3 vertebra were also measured.

RESULTS

One in eighty cases (1.2%) belonged to Type 1 with a B Length of 32.12 mm. Most cases (61.3%) were Type 2 with a B Length of 8.7 mm, while Type 3's was - 9.7 mm occupying for 37.5%. Significant statistic differences were found in anterior skull base angle between these three types (128.9°, 122.7° and 118.5° for Type 1, 2 and 3, respectively). The distances from Point A to the top and bottom portion of the clivus and the pharyngeal tubercle were 97.5, 96.0 and 96.8 mm, respectively. The angles between the tangent of the clivus and the lines from Point A to the above three structures were 75.7°, 92.3° and 84.0°, respectively. The distances from Point A to the middle point of anterior margin of C1 anterior tubercle, C2 vertebra and C3 vertebra were 79.1, 73.4 and 61.5 mm, respectively.

CONCLUSION

The clivus screw and plate placement could be accomplished with optimal screw angle by transoral approach in most of patients. Mandibular splitting would be needed in patients with greater anterior skull angle. These slides can be retrieved under Electronic Supplementary Material.

The Anatomic Study of Intracranial Structures Related to Clival Screw Placement

BACKGROUND

A clival plate and screw fitted to the craniovertebral junction (CVJ) were developed in our previous studies. However, the anatomy of intracranial structures related to clival screw placement has not been studied.

OBJECTIVE

To measure the intracranial anatomic parameters delineating the basilar plexus and vertebrobasilar artery (VBA) course and to determine the relationship between brainstem and clivus for safer screw placement.

METHODS

Morphometric analysis of the VBA was conducted on 95 patients (48 men, 47 women) by CT angiography (CTA) and of the basilar plexus and brainstem on 80 patients (44 men, 36 women) by magnetic resonance imaging (MRI) The narrowest distance between the VBA and the intracranial clivus and the distance between the VBA and the median line of the skull were measured on the axial plane at different parts. The relative positions of point I (intersection of vertebral artery and basilar artery) and the pharyngeal tubercle were analyzed. The distance between the clivus and the brainstem was measured at different levels.

RESULTS

As the VBA ascended the distances to the intracranial clivus and the midline decreased. In 83.3% cases, point I was above the pharyngeal tubercle, and in only 9.5% cases was it located on the vertical line drawn from pharyngeal tubercle. The smallest safe space between the intracranial clivus and the brainstem was 7.46 mm at the lower part.

CONCLUSION

Appropriate screw size at the lower clivus and the pharyngeal tubercle may help avoiding inadvertent injury to the brainstem and the VBA. Preoperative CTA and MRI of the CVJ are suggested to guide the surgeon in this regard.