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.


METHODS
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.


RESULTS
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.
Department of Spinal Surgery, Ningbo Sixth Hospital, Zhejiang Province, China. huyong610@163.com
Yong
Y
Hu
Yong-jie
YJ
Gu
Xian-feng
XF
He
Rong-ming
RM
Xu
Wei-hu
WH
Ma
Wei-dong
WD
Zhao
Dong-zhu
DZ
Liang
Shi-zhen
SZ
Zhong
D000328:Adult; D019643:Arthroplasty, Replacement / Q000295:instrumentation / Q000379:methods*; D001268:Atlanto-Axial Joint / Q000503:physiopathology / Q000601:surgery*; D001696:Biomechanical Phenomena; D001863:Bone Screws; D005260:Female; D006801:Humans; D007595:Joint Prosthesis; D008297:Male; D008422:Materials Testing / Q000379:methods; D008875:Middle Aged; D011475:Prosthesis Failure; D016059:Range of Motion, Articular