Artificial atlanto-odontoid joint replacement through a transoral approach

Abstract

Resection of the odontoid process and anterior arch of the atlas results in atlantoaxial instability, which if left uncorrected may lead to severe neurological complications. Currently, such atlantoaxial instability is corrected by anterior and/or posterior C1-C2 fusion. However, this results in considerable loss of rotation function of the atlantoaxial complex. From the viewpoint of retaining the rotation function and providing stability, we designed an artificial atlanto-odontoid joint based on anatomical measurements of 50 pairs of dry atlantoaxial specimens by digital calipers and 10 fresh cadaveric specimens by microsurgical techniques. The metal-on-metal titanium alloy joint has an arc-shaped atlas component, and a hollow cylindrical bushing into which fits a rotation axle of an inverted v-shaped axis component and is implanted through a transoral approach. After the joint was implanted onto specimens with anterior decompression, biomechanical tests were performed to compare the stability parameters in the intact state, after decompression, after artificial joint replacement, and after fatigue test. Compared to the intact state, artificial joint replacement resulted in a significant decrease in the range of motion (ROM) and neutral zone (NZ) during flexion, extension, and lateral bending (P < 0.001); however, with regard to axial rotation, there was no significant difference in ROM (P = 0.405), a significant increase in NZ (P = 0.008), and a significant decrease in stiffness (P = 0.003). Compared to the decompressed state, artificial joint replacement resulted in a significantly decreased ROM (P B 0.021) and NZ (P B 0.002) and a significantly increased stiffness (P \ 0.001) in all directions. Following artificial joint replacement, there was no significant difference in ROM (P C 0.719), NZ (P C 0.580), and stiffness (P C 0.602) in all directions before and after the fatigue test. The artificial joint showed no signs of wear and tear after the fatigue test. This artificial atlanto-odontoid joint may be useful in cases of odontoid resection due to malunion or nonunion of odontoid fracture, atraumatic odontoid fracture, irreducible atlas dislocation, posterior atlantoaxial subluxation, or congenital skull base abnormalities.

Biomechanical evaluation of stability and three-dimensional movements of the atlantoaxial joint after artificial atlanto-odontoid joint arthroplasty

“…It is believed that the ROM in the NZ is more sensitive for assessment of stability 20–22 . In this study, biomechanical analysis of three‐dimensional movement in human cervical spine specimens showed that the ROM in flexion, extension, lateral bending and rotation after AAOJ arthroplasty was definitely decreased compared with anterior decompression, but the ROM of rotation and the range of the NZ were close to normal, these findings being the same as those reported by Lu et al 2,3 …”

“…It is believed that the ROM in the NZ is more sensitive for assessment of stability [20][21][22] . In this study, biomechanical analysis of three-dimensional movement in human cervical spine specimens showed that the ROM in flexion, extension, lateral bending and rotation after AAOJ arthroplasty was definitely decreased compared with anterior decompression, but the ROM of rotation and the range of the NZ were close to normal, these findings being the same as those reported by Lu et al 2,3 . The abovementioned results may be due to the following factors: (i) the distance between the apical odontoid ligament and basion was kept close to normal to ensure a normal ROM of the occipitocervical region in anterior flexion (in the normal occipitocervical spine, anterior flexion is subject to contact between the apical odontoid ligament and basion, and posterior extension is confined by contact between the base of the occipital bone and posterior arch of the atlas, and traction on the tectorial membrane); (ii) the locking link of the atlanto-odontoid joint was rebuilt to ensure that the axis of rotation was restricted to the joint itself, so that various types of movement occurred as they do under normal conditions and the remaining joint capsule and ligaments maintained their normal functions; and (iii) excessive sliding (right/left or front/back) was restricted, because movement of the normal atlantoaxial joint at different angles is coupled with sliding and the ROM of sliding also constrains the ROM of angular movement to a certain extent.…”

“…Through a transoral approach, it can both reconstruct the stability and preserve the motor function of the atlantoaxial joint in a one stage procedure 1 . However, the reported AAOJ is very basic and crude, and is not capable of preventing laxity and deterioration of the joint in the long term 2,3 . Anatomical study has demonstrated that the self-designed AAOJ arthroplasty (made by Guangci Medical Appliances, Ningbo, China, Patent No: ZL2006 2 0140259.7) is feasible from a morphological point of view and has outstanding advantages over traditional upper cervical spinal fusion 4,5 .…”

Radiological and surgical anatomy of ventral c1-c2 complex

“…In our study, the width of the C1 lateral mass is 12.86 ± 0.87 mm. The same parameter was measured as 9.5 ± 1.0 mm by Rocha et al (13), and 14.1 ± 1.5 mm by Lu et al (12).…”

Artificial Cervical Vertebra and Intervertebral Complex Replacement through the Anterior Approach in Animal Model: A Biomechanical and In Vivo Evaluation of a Successful Goat Model

“…For the biomechanical study of artificial joints in the spine, human cadavers [21], [22] and animal models have been well studied. Human cadavers have the same biomechanical properties as living humans, but they are precious and their use raises ethical issues; furthermore, they cannot be used to evaluate the in vivo reactions of human vertebrae with artificial joints.…”