Biomechanical study of artificial atlanto-odontoid joint

Study Design. An in vitro biomechanical study. Objective. To determine the initial stability and function of a new artificial joint in a cadaveric cervical spine model by comparing it with a conventional method. Summary of Background Data. Resection of the odontoid and anterior arch of the atlas results in atlantoaxial instability, which if left uncorrected may lead to severe neurologic complications. Currently, such atlantoaxial instability is corrected by anterior and/or posterior C1–C2 fusion. Methods. There were 24 fresh human cadaveric cervical spines (C0–C3) randomly divided into 2 groups: group 1, resection of the odontoid with artificial atlanto-odontoid joint (AAOJ); and group 2, resection of the odontoid with Harms anterior atlantoaxial plate (Harms). For each specimen, the intact and resection of the odontoid underwent a flexibility test first, followed by the instrumented construct. Rotational angles of the C0–C3 segment were measured to study the immediate stability and function of resection of the odontoid and AAOJ, compared with the intact and resection of the odontoid and Harms. Results. Compared with the intact state, resection of the odontoid and AAOJ resulted in a significant decrease in the range of motion (ROM) and neutral zone during flexion, extension, and lateral bending (P 0.05). Compared with resection of the odontoid and Harms, resection of the odontoid and AAOJ during flexion, extension, and lateral bending, there was no significant difference in ROM (P > 0.05). Conclusion. We have designed a new type of AAOJ for correcting atlantoaxial instability arising from C1 to C2 anterior decompression procedures. The unique aspect of this joint is that it restores, to a great extent, the C1–C2 axial rotation that is lost during current stabilization procedures.