[The biomechanical study of craniovertebral junction fixation with posterior transarticular screw].
OBJECTIVE
To evaluate the stability of biomechanics of occipitoatlantoaxial reconstruction with transarticular screw fixation.


METHODS
Twelve fresh human cadaveric occipitocervical spine specimens were mounted in a custom-designed, spine-testing machine that applied pure moments while recording the three-dimensional angular movement at occiput (Oc)-C(1) and C(1 - 2) segments. The specimens were tested under seven different conditions: the intact (intact group), the occipitoatlantoaxial instability (Destabilized group), fixation with Ti-cable plus bone graft group (cable + graf group), fixation with the transarticular fixation (CTS group), fixation with SUMMIT occitocervical spinal fixation system (SUMMIT group), fixation with transarticular screw plus bone graft (CTS + graf group), and fixation with SMMIT system and plus graft group (SUMMIT + graf group). The data obtained were statistically analyzed.


RESULTS
The CTS group reduced motion to well within the normal rang. In the Oc-C(1) segment, The CTS group and SUMMIT group allowed a very small rang of motion (ROM) and neutral zone (NZ) during lateral bending and axial rotation. The ROM and NZ during flexion and extension of the SUMMIT group, were significantly smaller than those of cable + graf group and CTS group (6.64 degrees +/- 0.59 degrees, 2.49 degrees +/- 0.26 degrees, 0.50 degrees +/- 0.03 degrees, 0.21 degrees +/- 0.01 degrees, 0.27 degrees +/- 0.07 degrees, 0.13 degrees +/- 0.01 degrees vs 10.01 degrees +/- 1.26 degrees, 3.80 degrees +/- 0.79 degrees, 7.93 degrees +/- 1.34 degrees, 3.18 degrees +/- 0.95 degrees, 9.54 degrees +/- 0.87 degrees, 5.93 degrees +/- 0.74 degrees, P < 0.05). In the C(1 - 2) segment, ROM and NZ in all directions of CTS group were smaller in rotation than SUMMIT group (1.64 degrees +/- 0.39 degrees, 0.61 degrees +/- 0.15 degrees, 0.14 degrees +/- 0.05 degrees, 0.02 degrees +/- 0.01 degrees, 0.32 degrees +/- 0.04 degrees, 0.08 degrees +/- 0.01 degrees, vs 0.21 degrees +/- 0.04 degrees, 0.07 degrees +/- 0.03 degrees, 0.21 degrees +/- 0.12 degrees, 0.10 degrees +/- 0.02 degrees, 2.92 degrees +/- 0.28 degrees, 1.27 degrees +/- 0.11 degrees, all P < 0.05). There was no significant difference in ROM and NZ in all directions between CTS + graf group and SUMMIT + Graf group (P > 0.05).


CONCLUSIONS
In vivo biomechanics studies show that posterior occipitocervical transarticular fixation has unique features in reconstructing dynamic stability of the occipitoatlantoaxis, especially in controlling stability of rotation and lateral flexion, thus ensuring successful fusion of the implanted bone and allowing for clinical use of the technique.
Yan
Wang-jun
WJ
Department of Orthopaedics, Changzheng Hospital, Second Military Medical University, Shanghai 200003, China. yanwangjun@yahoo.com.cn
Cai
Bin
B
Chen
Yu
Y
Yuan
Wen
W
Li
Jia-shun
JS
Jia
Lian-shun
LS
Yang
Guo-biao
GB
Zeng
Wei-ming
WM
D000328:Adult; D000368:Aged; D001268:Atlanto-Axial Joint / Q000503:physiopathology* / Q000601:surgery*; D001696:Biomechanical Phenomena; D001863:Bone Screws; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D016896:Treatment Outcome