Biomechanical experiment on transoral atlantoaxial reduction plate

Abstract

Objective To study biomechanical stability,including rang of motion(ROM)and pull-out strength of screws,of transoral atlantoaxial reduction plating(TARP). Methods Twelve flesh C0～C3 spine specimens were harvested.Six specimens were designed to compare ROM of TARP in 4 clinical anterior-posterior atlantoaxial arthrodeses in 7 groups:intact(control),injured,TARP,Brooks,Magerl,Magerl+Brooks,and anterior transarticular screw fixation through C2 vertebral body.The other 6 specimens (totally 12 sides)were designed to compare pull-out strength of screws,screw path length and failure length of C1,C2 and C3 in 3 groups:atlas,axis,and C3(control). Results No statistically significant difference in ROM was observed between TARP and Magerl+Brooks(P＞0.05),with the ROM of TARP slightly wider than that of the latter.The ROM of flexion-extension,lateral bending and axial rotation of the above 2 were smaller than those of the other 3 fixators(P＜0.05).There were statistically significant differences in screw pull-out strength and screw path length between C1 and C2 and C3(Pull-out strength:C1=491.58 4±67.92 N,C2=396.73±60.99 N,C3=385.53±96.77 N)(P＜0.05).No statistically significant differences were observed in screw pull-out strength and path length between C2 and C3(P＞0.05).There was no significant difference in screw failure length between C1-C3(P＞0.05).The screw pull-out strength was positively correlative to the path length and failure length(correlation coefficients:r=0.810 and r=0.652 respectively)(both P＜0.05).The screw pull-out strength was more correlative to the path length than to the failure length(P＜0.05). Conclusions Experimentally,TARP has the same effect with Magerl+Brooks and they provide more stability than the other 3 widely used atlantoaxial fixators:Magerl,Brooks and anterior transarticular screw fixation through C2 vertebral body.The TARP screws of Cl and C2 are strong enough for atlanto-axial arthrodesis.Screw path length and failure length are important factors influencing screw pull-out strength. Key words: Atlanto-axial joint; Arthrodesis; Internal fixators; Biomechanics