Anatomy and biomechanical test comparison between fixation techniques of atlas pedicle screw and fixation techniques of atlas lateral mass screw

Objective To compare the anatomy and biomechanical test difference between atlas pedicle screw and atlas lateral mass screw,and provide theoretical basis for reasonable clinical choice of the posterior atlas screw fixation technique.Methods The relative parameters of sixteen sets of fresh Chinese adults' atlas specimens were measured with an digital caliper and a goniometer,including The mean maximum length of C1 lateral mass screw(L1),the distance from its entry point to posterio redge of C1 posterior arch(L2)、in the lateral mass of C1(L3)、in the posterior arch(L4) and the averaged maximum length of C1 pedicle screw(L3+L4)and so on.The extraversion and upslope angle of atlas pedicle screw and atlas lateral mass screw.The unicortical and bicortical lateral mass screw or pedicle screw were placed on atlas in sixteen fresh spine specimens separately.The length and the pull-out strength of the screw were measured and tested.Results The mean maximum length of C1 lateral mass screw(L1)was 25.01±0.23mm,the distance from its entry point to posterio redge of C1 posterior arch was(L2)9.85±1.31mm.The averaged maximum length of C1 pedicle screw(L3+L4)was 29.8±1.27mm,10.47±1.51 mm was in the posterior arch(L4),19.58±1.63ram was in the lateral mass of C1(L3).The extraversion and upslope angle of atlas pedicle screw and atlas lateral mass screw was respectively 10~(?),5(?)and 15(?),20(?)Atlas bicortical pedicle screw was the strongest fixation method.Its pull-out strength averaged(1686.0±425.3)N.No statistically significant difference was observed between atlas unicortical pedicle screw (1082.5±292.7)N and atlas bicortical lateral mass screw(1127.2±367.1)N.atlas unicortical lateral mass screw(785. 2±402.7)N was the weakest fixation technique.Conclusion Because of difference entry point between atlas pedicle screw and atlas lateral mass screw,atlas pedicle screw was longer than atlas lateral mass screw.Due to the extraversion and upslope angle of atlas lateral mass screw was bigger than atlas pedicle screw,length of atlas lateral mass screw was longer than in the lateral mass of atlas pedicle screw.In a giving patient,it would be better to choose C1 pedicle screw than C1 lateral mass screw,if he or she is suitable for both techniques.