固定期放疗对兔下颌骨牵张成骨术中新骨形成影响的实验研究

目的研究固定期放疗对兔下颌骨牵张成骨新骨形成的影响。方法 30只成年新西兰大耳白兔随机分成A、B、C三组,A组实验动物行双侧下颌骨皮质骨切开术并植入牵张器,5d后开始骨牵引,速率为0.5mm/次,2次/d,连续10d,共延长下颌骨10mm,固定10周;B组实验动物行双侧下颌骨皮质骨切开、植入牵张器,进行骨牵张,牵张结束后固定10周,并在固定4周后开始用直线加速器照射双侧下颌骨,5.4Gy/次,隔日1次,共5次,总剂量为27Gy;C组动物为对照组。固定期结束处死动物后,取各组动物牵张区新生骨痂行X线检查、组织学观察、骨形态计量学分析、骨密度测定及三点弯曲试验测试牵引区抗弯强度。结果大体观察和X线检查显示所有进行下颌骨牵张的实验动物牵张间隙均有新骨形成,骨小梁沿牵张方向排列,骨密度较高;组织学观察显示A组实验动物牵张区均充满排列整齐的新生编织骨,B组可见较多的胶原纤维成发及软骨岛,新生骨小梁不及A组致密、成熟;骨形态计量学分析和机械力学分析结果显示B组的新生骨在骨密度和新生骨小梁数目上与A组比较无统计学差异,但是在新骨矿化程度方面,固定期放疗组较差,其机械强度也较低(P<0.05)。结论在牵张成骨术的固定期进行放疗仍可以出现牵张区的新生骨形成,但软骨成分较多,机械强度较低。牵张成骨术用于颌骨恶性肿瘤切除术后颌骨早期重建是可行的。

The effect of radiotherapy on bone formation in rabbit mandible distraction during consolidation phase

Objective To evaluate the effect of radiotherapy on new bone formation in rabbit mandibles distraction during consolidation period.Methods Thirty New Zealand white rabbits were randomly divided into three groups.Group A received corticotomy in both sides of mandible and then began to activate 5 days after surgery.The distractor was stretched 0.5 mm each time and two times each day in the distraction period of 10 days.The fixation period was 10 weeks.Group B were treated as Group A in the beginning.While at 4 weeks after consolidation,Group B was irradiated by linear accelerator with 27 Gy in 5 fractions which was 5.4 Gy in each time every other two days.All animals were sacrificed 10 weeks after consolidation,and the callus in distraction area were harvested and assessed by X-ray photograph,histological observation,bone histomorphometry analysis,bone densitometry,as well as biomechanical test.Results New bone formation can be obtained in all distracted mandibles.X-ray examination showed no significant difference of new bone formation between irradiated and non-irradiated group.Histological observation showed new woven bone lining up in order can be obtained in all groups while there were more cartilage islands in the irradiated group and less mature.The contents of bone histomorphometry also supported the histological findings and the bone density analysis showed no difference between irradiated bone and normal distracted bone.The result of 3-point bending test demonstrated the biomechanical strength of new formed bone of no-irradiated group was better.Conclusions It seems that radiotherapy is feasible in the early stage of consolidation during osteogenesis distraction,although the new bone contains more cartilage component and lower mechanical strength.