Abstract
BackgroundBasilar invagination (BI) combined with atlantoaxial dislocation (AAD) leads to foramen magnum stenosis and medullary spinal cord compression, causing nerve dysfunction. The purpose of the surgery is to remove the bony compression at brainstem ventral side and fix the unstable spinal segment and make it fused stably. Occipital cervical internal fixation system that simultaneously reduces atlantoaxial horizontal and vertical dislocation are established. We propose here a new compression-distraction reduction (CDR) technique. We aimed to construct a congenital BI-AAD preoperative finite element model (FEM) to simulate the CDR technique for AAD reduction surgery.MethodsBased on computed tomographic scans of patients’ cervical vertebrae, a three-dimensional (3D) geometric model of the cervical spine (C0–C4) of congenital BI-AAD patients was established using Mimics13.1, Geomagic2012, and Space Claim14.0 softwares. The mechanical parameters of the tissues were assigned according to their material characteristics using ANSYS Workbench 14.0 software. A 3D FEM was established using the tetrahedral mesh method. The bending moment was loaded on C0. Physiological conditions—anteflexion, retroflexion, left and right flexion, left and right rotation—were simulated for preoperative verification. The occipital cervical fixation system FEM was established. The CDR technique was simulated to perform AAD reduction surgery. Data were obtained when the atlantoaxial horizontal and vertical dislocation reductions were verified postoperatively. Stress data for the two surgical schemes were analyzed, as was the reduction surgery optimization scheme for congenital BI-AAD patients with abnormal lateral atlantoaxial articulation ossification.ResultsCervical spine (C0–C4) FEM of congenital BI-AAD patients was established. The CDR technique was simulated for AAD reduction. We obtained the mechanical data when the atlantoaxial horizontal and vertical dislocation reductions were satisfied for the two surgical schemes.ConclusionsThe CDR technique for AAD reduction was feasible and effective. We propose this reduction optimization scheme for patients with lateral atlantoaxial articulation due to abnormal ossification of congenital BI-AAD. We also provide a biomechanically theoretical basis for improving the reliability of pure posterior reduction surgery and simplifying surgery for complicated BI-AAD disease.
Highlights
Basilar invagination (BI) combined with atlantoaxial dislocation (AAD) leads to foramen magnum stenosis and medullary spinal cord compression, causing nerve dysfunction
The odontoid process and the position of C1 are consistent with the postoperative computed tomography (CT) measurement data, occlusion of the odontoid process and joint surfaces on C1 is inconsistent with the postoperative CT, which might be due to the CT image data having been obtained 6 months after surgery when fusion had already occurred
The compression-distraction reduction (CDR) technique was simulated for AAD reduction surgery on the abovementioned congenital basilar invagination atlantoaxial dislocation (BI-AAD) patient
Summary
Basilar invagination (BI) combined with atlantoaxial dislocation (AAD) leads to foramen magnum stenosis and medullary spinal cord compression, causing nerve dysfunction. The purpose of the surgery is to remove the bony compression at brainstem ventral side and fix the unstable spinal segment and make it fused stably. The primary purpose of surgical treatment for complicated basilar invagination and atlantoaxial dislocation is to remove the ventral bony compression of the brainstem. For atlantoaxial dislocation, which can be reduced, posterior occipital cervical internal fixation fusion surgery can be performed in the case of atlantoaxial reduction by skull traction. After reducing the atlantoaxial dislocation by skull traction, posterior occipital cervical fixation fusion surgery [2,3,4,5] should be carried out. The clinical treatment is gradually changing from conventional anterior release, traction, reduction, and posterior fusion to a simpler posterior cutting-reduction-fixation technique
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