Hangman骨折侧方椎弓螺钉固定力学测试

Biomechanical Study of Screw Fixation of Lateral Arch in the Treatment of Hangman' Fracture

目的比较Hangman骨折采用不同方法进行侧方椎弓螺钉固定时椎板的骨折暴力和螺钉的拔出力。方法8例包含枢椎的新鲜颈椎标本利用计算机重建技术模拟寻找出进针点和进针方向后,造成Ⅰ型Hangman骨折模型,分为单侧单纯侧方椎弓螺钉固定组(A组,2例4侧)、双侧单纯侧方椎弓螺钉固定组(B组,4例8侧)和单侧加垫圈侧方椎弓螺钉固定组(C组,2例4侧),钻入3.5mmAO皮质骨螺钉后进行螺钉拔出试验。结果A、B两组在螺钉拔出前均发生钉孔周围椎板骨质的凹陷或骨折,椎板骨折暴力分别为(11.58±3.18)kg(8.5～16.0kg)和(25.75±2.4)kg(22.5～28.3kg),螺钉拔出力分别为(29.65±3.89)kg(25.0～33.6kg)和(30.90±3.99)kg(26.8～38.0kg)。C组未见钉孔周围椎板骨折发生,螺钉拔出力为(33.83±4.20)kg(28.0～37.0kg)。结论在用侧方椎弓螺钉固定治疗Hangman骨折时,AO皮质骨螺钉钉尾添加垫圈可使钉孔处椎板抗骨折暴力明显增强,大于螺钉的拔出力。单侧垫圈螺钉固定组的固定效果略优于双侧单纯皮质骨螺钉固定的效果。

Objective To study the breakage force of lamina around or adjunct to the head of screw and the pull-out strength of screw (A0 3.5 mm cortical screw) inserted into uni-or bi-lateral arch of axis to fix Hangman’s fracture with or without a bevel washer being used beneath the head of screw. Methods Eight fresh cervical vertebra of health cadaver were classified into three groups randomly with the isthmus of axis fractured by an osteotom to establish typical Hangman’s fracture model after the entrance point and trajectory orientation of lateral arch screw of axis was determined with the help of 3-D reconstructive software (Unigraphics NX). Group A: unilateral arch screw fixation without a bevel washer, four lateral arches in two axes were included in the group; Group B: bilateral arch screw fixation without affiliation of bevel washer, four axes were included in this group; Group C: unilateral arch screw fixation with the affiliation of a bevel washer, four lateral arches in two axes were included. Results Fracture of lamina around the head of screw occurred before the lateral arch screw was pulled out in group A and B, while the breakage forces of lamina in group A and Group B were (11.58±3.18)kg (8.5 to 16.0 kg) and (25.75±2.41)kg (22.5 to 28.3 kg), respectively. The pull-out force of screw those were (29.65±3.89)kg(25.0 to 33.6 kg and (30.90±3.99)kg(26.8 to 38.0 kg), respectively. No fracture of lamina was found in group C before and after the screw was pulled out, the pull-out strength of screw was (33.83±4.20)kg (28.0 to 37.0 kg), which was statistically different compared with the pull-out force of Group A or B, and was superficially greater than the breakage force of lamina in Group B. Conclusion Adding a bevel washer provids a larger surface area of the cortex for the screw head and increares the breakage force of lamina obviously. Compared to bilateral arch screw fixation without affiliation of bevel washer, mono-sided lateral arch screw fixation with a bevel washer may be superior in the treatment of Hangman' fracture.