The anatomical study of transoral atlantoaxial reduction plate internal fixation

摘要

Objective; To study relevant anatomical features of the structures involved in transoral atlanto-axial reduction plate (TARP) internal fixation through transoral approach for treating irreducible atlanto-axial dislocation and providing anatomical basis for the clinical application of TARP. Methods: Ten fresh craniocervical specimens were microsurgically dissected layer by layer through transoral approach. The stratification of the posterior pharyngeal wall, the course of the vertebral artery, anatomical relationships of the adjacent structures of the atlas and axis, and the closely relevant anatomical parameters for TARP internal fixation were measured. Results: The posterior pharyngeal wall consisted of two layers and two interspaces: the mucosa, prevertebral fascia, retropharyngeal space, and prevertebral space. The range from the anterior edge of the foramen magnum to C_3 could be exposed by this approach. The thickness of the posterior pharyngeal wall was (3.6 ±0.3) mm (ranging 2.9-4.3 mm) at the anterior tubercle of C1, (6.1±0.4) mm (ranging 5.2-7.1 mm) at the lateral mass of C_1 and (5.5 ±0.4) mm (ranging 4.3-6.5 mm) at the central part of C_2, respectively. The distance from the incisor tooth to the anterior tubercle of C_1, C_1 screw entry point, and C_2 screw entry point was (82. 5 ± 7. 8) mm (ranging 71. 4-96. 2 mm) , ( 90. 1 ± 3. 8 ) mm ( ranging 82.2-96. 3 mm), and (89. 0 ± 4. 1) mm ( ranging 81. 3-95.3 mm), respectively. The distance between the vertebral artery at the atlas and the midline was (25. 2 ± 2.3) mm (ranging 20.4-29. 7 mm) and that between the vertebral artery at the axis and the midline was (18. 4 ± 2.6) mm (ranging 13.1-23.0 mm). The allowed width of the atlas and axis for exposure was (39. 4 ± 2. 2) mm (ranging 36. 242. 7 mm) and (39.0 ±2.1) mm (ranging 35.842.3 mm), respectively. The distance (a) between the two atlas screw insertion points ( center of anterior aspect of C_1 lateral mass) was (31.4 ±3.3) mm (ranging 25.4-36.6 mm). The vertical distance (b) between the line connecting the two C_1 screw entry points and that connecting the two C_2 screw entry points (at the central part of the vertebrae, namely 34 mm lateral to the midline of C_2 vertebrae) was (21. 3 ± 2. 7) mm ( ranging 19. 4-24.3 mm) , with an a/b ratio of 1.3-1.5. The screws of TARP had a lateral tilt of 12.2° ±0.4° (ranging 10.2°-14.6°) at C_1 and a medial tilt of 7.3° ±0.3° (ranging 5.1°-9.4°) at C_2 relative to the coronal plane. Conclusions: An atlanto-axial surgery through transoral approach is safe and feasible. This approach is suitable for an anterior TARP internal fixation, and the design of the internal fixation system should be based on the above anatomical data.