Biomechanical evaluation of the Total Atlanto-odontoid Joint Arthroplasty System: an in vitro human cadaveric study.

Abstract

Atlanto-odontoid joint arthroplasty is a motion restoring procedure suggested as an alternative to rigid fixation after surgical decompression. The purpose of this study was to evaluate the kinematics and pullout strength of a novel Total Atlanto-odontoid Joint Arthroplasty System using human cadaveric specimens. Nondestructive biomechanical tests were performed on 24 fresh craniocervical specimens separated into two groups: 1) the prosthesis implantation group and 2) Harms transoral atlantoaxial plate fixation group. The following configurations were investigated: intact, after decompression, and instrumented. Range of motion and neutral zone were calculated for the C1-C2 segment. In a second experimental series, 8 sets of fresh atlantoaxial specimens were used to test the pullout strength of the atlas-axis components. Compared with Harms rigid fixation, the Total Atlanto-odontoid Joint Arthroplasty System significantly increased the range of motion and neutral zone in all directions (P<.001). In addition, compared with the intact state, the only significant change in the range of motion and neutral zone with the Total Atlanto-odontoid Joint Arthroplasty System implantation was an increase in lateral bending (P<.001). The pullout strength created by the anterior C2 transpedicular screw was greater than that of the C2 vertebral screw and C1 lateral mass screw (P<.001), and the C1 lateral mass screw was stiffer than the C2 vertebral screw (P=.02). Biomechanical analyses suggest that the Total Atlanto-odontoid Joint Arthroplasty System was able to provide reliable fixation strength and preserve the normal kinematics of the C1-C2 segment after decompressive procedures.