BONE REMODELING IN THE CALLUS FORMED DURING -DISTRACTION OSTEOGENESIS

本研究的目的是阐明牵张成骨过程中骨重塑的机制。实验研究对象为30只体重约2.0 kg的日本大白兔。右侧胫骨采用单侧外固定架，骨干中段行截骨术。等待7天后，以0.7 mm/d的速度进行慢速牵张，持续3周。牵张间隙自然被愈伤组织填满，愈伤组织有三个不同的区域。伸长发生在中央辐射区，由两个硬化区隔开。新形成的愈伤组织被迅速吸收和重塑，留下新的皮层。为了研究双膦酸盐对骨愈合和骨痂重塑的影响，我们以高剂量（0.4mg/Kg/周）和低剂量（0.004mg/Kg/周）静脉注射米诺膦酸盐。术后7周（牵张完成后3周）处死动物，软x线分析测定骨密度。实验结果表明，大剂量米诺膦酸钠能明显促进骨愈合。二膦酸盐给药动物的延长节段骨密度比对照动物高得多。三点弯曲试验显示，双膦酸盐给药组的延长节段力学稳定性高于对照组。延长节段的组织形态学研究表明，双膦酸盐不改变破骨细胞的数量，但会干扰破骨细胞的功能，从而抑制牵张成骨过程中骨吸收和骨重塑

The purpose of this study is to elucidate the mechanism of bone remodeling in the callus formed during distraction osteogenesis. The experimental study was carried out on 30 Japanese white rabbits weighing about 2.0 kg. A unilateral external fixator was applied to the right tibia and osteotomy was achieved in the mid-diaphysis. After 7 days of waiting period, slow distraction was carried out at a rate of 0.7 mm/day for three weeks. Distraction gap was spontaneously filled with the callus having three distinct zones. Elongation occurred in a central radiolucent zone, which was bounded by two sclerotic zones. Newly formed callus was resorbed and remodeled quickly, leaving a new cortex. In order to examine the effects of bisphosphonate on bone healing and remodeling of the callus, minodronate was administrated intravenously at high dose (0.4mg/Kg/week) or at low dose(0.004mg/Kg/week). The animal was killed 7 weeks after operation (3 weeks after completion of distraction), and bone mineral density was measured by soft X-ray analysis. Experimental results showed that bone healing was definitely accelerated by administration of high dose of minodronate. The bone mineral density of the lengthened segments was much higher in the bisphosphonate-administrated animals than in control animals. Three point bending test showed higher mechanical stability of the lengthened segment in bisphosphonate-administrated group than in control group. Histomorphometric study of the lengthened segments demonstrated that bisphosphonate did not change the number of osteoclasts but disturbe the function of osteoclasts and consequently suppressed bone resorption and remodeling of the callus during distraction osteogenesis