BAcKGROUND:In recent years,the pedicle screws fixation technique,which is used in fixation for atlantoaxial instability associated with trauma,severe degeneration and tumorectomy,has been developed.However,this kind of technique easily causes several complications,including malpositional screws,vascular injuries,and even vertebral artery injury.Based on the biomechanical characteristics of memory alloy and determination of atlantoaxial data,a neotype shape memory alloy cervical hook was designed to treat atlantoaxial instability.OBJECTIVE:To investigate the biomechanieal characteristics of the neotype shape memory alloy cervical hook for atlantoaxial instability.DESIGN,TIME AND SETTING:Repeated measurement analysis of variance test was performed in the Laboratory of Clinical Anatomy and Medical Biomechanics,Southern Medical University between March and April 2008.MATERIALS:Eight fresh adult craniocervical specimens(C0-C4)were provided by Department of Clinical Anatomy,Southern Medical University.Atlantoaxial neotype shape memory alloy cervical hook(50.8%-51.8%nickel and the remaining part was titanium)was fabricated by Shanghai Xinchang Memory Alloy Co.,Ltd.METHODS:The included eight C0-C4 specimens were used to test three-dimension ranges of motion(ROM)by fixation and neotype shape memory alloy cervical hook fixation.Then,the positions of spine varying from no loading to the maximum loading status were scanned and analyzed using image processing software to determine the three-dimensional ROM under different statuses.MAIN OUTCOME MEASURES:Three-dimensional ROM of tested specimens.RESULTS:Neotype shape memory alloy cervical hook fixation and Germany AESCULAP SSE hanger fixation had similar flexion-extension range of motion(P=0.595).Lateral bending three-dimensional ROM was greater in the neotype shape memory alloy cervical hook fixation group than in the Germany AESCULAP AAE hanger fixation(P< 0.05).The rotatory three-dimensional ROM was smaller in the neotype shape memory alloy cervical hook fixation group than in the Germany AESCULAP AAE hanger fixation(P<0.05).CONCLUSION:Neotype shape memory alloy cervical hook fixation had comparative post-surgery immediate stability with the Germany AESCULAP AAE hanger fixation.Neotype shape memory alloy cervical hook fixation produced a little worse biomechanical lateral bending stability and a little better biomechanical rotatory stability than Germany AESCULAP AAE hanger fixation.