Thoracic Pedicle Screw Fixation Failure In Transpedicular Into The Road To Remedy Biomechanical Study

Objective.1. To compare the pullout resistance of thoracic extrapedicular screws with intrapedicular screws and identify whether extrapedicular can be used instead of intrapedicular screws.2. To compare the pullout resistance of revised intrapedicular screws with extrapedicular screws and identify whether extrapedicular can be used as salvage for failed intrapedicular screws.Methods.1. Four human cadaveric thoracic spines(T6-T11) were harvested and disarticulated into 24 vertebra rib units from the following lever:intervertebral disk,facet articulation and inferior costovertebral articulation.The follow parameters were recorded①The screw length of intrapedicular;②The transverse diameter of intrapedicular;③The sagittal angle of intrapedicular;④The screw length of extrapedicular;⑤The transverse diameter of extrapedicular;⑥The sagittal angle of extrapedicular.2. According to the principle of paired grouping ,these specimens were divided into four groups(1) intrapedicular screws;(2) extrapedicular screws;(3) revised intrapedicular screws;(4) revised extrapedicular screws. Pullout tests were performed and maximum Pullout resistance of each srew was noted. Pullout resistance of intrapedicular screws were recorded as control data. Results.1. The difference in pullout strength between theintrapedicular(793.42±204.56N) and extrapedicular (775.33±148.57N)screw groups demonstrated no significance(P=0.613).2. The difference in pullout strength between the salvage of intrapedicular (522.33±172.80N) and extrapedicular (661.67±158.51N)screw groups was signficant(P<0.05).The pullout strength of intrapedicular used as salvage was smaller significantly than intrapedicular and extrapedicular screw groups(P<0.05).However, the pullout strength of extrapedicular used as salvage was not significant(P=0.162).Conclusion.Extrapedicular screws may be regarded as a supplementary of intrapedicular screws.Extrapedicular screws may be regarded as a salvage procedure for failed intrapedicular screws which destroyed medial wall of thoracic pedicle.