C2 Screw fixation techniques in atlantoaxial instability: A technical review

Study on articular surface morphology of atlantoaxial lateral mass based on differential manifold

OBJECTIVES

To propose a surface reconstruction algorithm based on a differential manifold (a space with local Euclidean space properties), which can be used for processing of clinical images and for modeling of the atlantoaxial joint. To describe the ideal anatomy of the lateral atlantoaxial articular surface by measuring the anatomical data.

METHODS

Computed tomography data of 80 healthy subjects who underwent cervical spine examinations at our institution were collected between October 2019 and June 2022, including 46 males and 34 females, aged 37.8 ± 5.1 years (28-59 years). A differential manifold surface reconstruction algorithm was used to generate the model based on DICOM data derived by Vision PACS system. The lateral mass articular surface was measured and compared in terms of its sagittal diameter, transverse diameter, articular surface area, articular curvature and joint space height.

RESULTS

There was no statistically significant difference between left and right sides of the measured data in normal adults (P > 0.05). The atlantoaxial articular surface sagittal diameter length was (15.83 ± 1.85) and (16.22 ± 1.57) mm on average, respectively. The transverse diameter length of the articular surface was (16.29 ± 2.16) and (16.49 ± 1.84) mm. The lateral articular surface area was (166.53 ± 7.69) and (174.48 ± 6.73) mm2 and the curvature was (164.03 ± 5.27) and (153.23 ± 9.03)°, respectively. The joint space height was 3.05 ± 0.11mm, respectively. There is an irregular articular space in the lateral mass of atlantoaxial, and both upper and lower surfaces of the articular space are concave. A sagittal plane view shows that the inferior articular surface of the atlas is mainly concave above; however, the superior articular surface of the axis is mainly convex above. In the coronal plane, the inferior articular surface of the atlas is mostly concave above, with most concave vertices located in the medial region, and the superior articular surface of the axis is mainly concave below, with most convex vertices located centrally and laterally.

CONCLUSION

A differential manifold algorithm can effectively process atlantoaxial imaging data, fit and control mesh topology, and reconstruct curved surfaces to meet clinical measurement applications with high accuracy and efficiency; the articular surface of the lateral mass of atlantoaxial mass in normal adults has relatively constant sagittal diameter, transverse diameter and area. The distance difference between joint spaces is small, but the shape difference of articular surfaces differs greatly.

C2 Superior Facetal Osteotomy: A Novel Technique in Complex Craniovertebral Junction Surgery for C1 Lateral Mass Screw Placement

Complex craniovertebral junction (CVJ) defects account for a considerable proportion of CVJ diseases. Given the heavily assimilated C1, an unfavorable C1-C2 joint orientation, an overriding C2 superior facet, a low-hanging occiput, and an abnormal vertebral artery course with a high-riding vertebral artery, placement of C1 lateral mass screws might be difficult. To address this, a novel technique for placing C1 lateral mass screws that avoid vertebral artery injury, low-hanging occiput, and overriding C2 superior facet was developed in this study. This approach enables firm fixation of C1-C2 even in difficult situations where the placement of the C1 lateral mass is challenging.