应力松弛接骨板对骨折愈合影响的实验研究

目的 探讨应力松驰接骨板体内应力遮挡率变化及其对骨折愈合的影响。方法 作兔两侧胫骨干截骨，分别以应力松弛接骨板（实验组）和坚硬接骨板（对照组）固定，术后２～４８周采用Ｘ线、光镜（含偏光）、及力学测试，对两组骨折愈合过程进行研究。结果 两组固定后，应力遮挡率均在７０％左右，随着固定时间的延长，实验组应力遮挡率逐渐下降，至术后８周，明显低于对照组；术后３６～４８周稳定在２７％左右。２～４周时，实验组外

Experimental study of effects of stress-relaxation bone plate system on healing of fracture

Objective To study the changes of stress shielding rate of Stress-relaxation plate in vivo and its in-fluences on healing of fracture. Methods Both Stress-relaxation plate (SRP) and Rigid plate (RP) were applied to os-tcotomized New Zealand rabbits tibia, The fracture healing process by fixing either with SRP or RP (control) under-went a comparative study by radiography, light (include polarized light) and biomechanical test from 2 to 48 weekspostoperatively. Results The stress shielding rate of fixing either with SRP or RP was about 70 % at the begining offixation, but the stress-shielding rate of SRP decreased gradually with prolongation of fixation time, by 8 weeks afterfracture, it was significantly lower than that of RP( P ＜ 0.05) and stabilized at 27% during 36-48 weeks after fixa-tion. According to the radiographic and histological examinations, there were abundant external callus around fracturesite accompanied by the formation of cartilaginous callus in SRP group during 2～4 weeks postoperatively, and startedto transform to lamellar bone with formation of new Hayer' s system and well organized collagen fibers by 8～12weeks. The mechanical strength of united bone restored gradually. As a control, in RP group, only a little of externalcallus formed at fracture site without formation of cartilaginous callus at the early stage of fracture, also the calius re-modeling became disordered and showed formation of resorption cavities in the synthetic bone at the later stage of frac-ture. These changes led to reduced mechanical strength of united bone in RP group, The ultimate bending strength(UBS) was only 57.95 percent of the normal rabbit' s tibia by 48 weeks. Conclusion The stress shielding rate of SRPreduces gradually with prolongation of fixation time, and has a good relativity with the fixation time, therefore, pro-vides an ideal mechanical environment which enhances callus formation and remodeling, favoring healing of fracturewith high mechanical strength. (Shanghai Med J, 2000,23: 734-737)