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

Objective: To investigate the stability and three-dimensional movements of the atlantoaxial joint after artificial atlanto-odontoid joint (AAOJ) arthroplasty.

Method: Ten sets of AAOJ implanted in bony specimens from 10 adults were used to test the pull-out strength of the atlas-axis components with a MTS858 Mini Bionix machine. Another twelve human cadaveric specimens including C(0)-C(4) were used to evaluate the three-dimensional movements of C(1)-C(2) under five different conditions in sequence, that is, the complete specimen, anterior decompression, posterior transarticular screws fixation, AAOJ arthroplasty and fatigue test.

Result: There were significant differences between atlas and axis components in the maximum pull-out strength and trajectory length, however the yield length was not significantly different. The maximum pull-out strength of the atlas and axis was positively correlated with trajectory length (r(1)= 0.880, P < 0.05) and yield length (r(2)= 0.606, P < 0.05), respectively. After AAOJ arthroplasty, the range of movement (ROM) with respect to rotation and the neutral zone of the atlantoaxial joint were close to normal (P > 0.05), but the ROM in flexion-extension and lateral bending was significantly smaller compared with the specimens which underwent anterior decompression (P < 0.05). No abrasion and abnormal mobilization were observed after 2000 cycles of flexion, extension, lateral bending and axial rotation in the fatigue test.

Conclusions: The self-designed AAOJ has excellent biomechanical performance, and AAOJ arthroplasty can restore excellent instant stability and preserve the movement of the atlantoaxial joint.