骨质疏松绵羊腰椎内不同椎弓根螺钉界面的组织学研究

Histological Comparison of Interfaces of Different Pedicle Screws in Osteoporotic sheep Lumbar Vertebrae

目的通过硬组织切片及染色技术观察骨质疏松绵羊腰椎内膨胀式椎弓根螺钉（expansive pedicle screw,EPS）与骨水泥强化螺钉（polymethylmethacrylate-augmented pedicle screw,PMMA-PS）的钉道界面。方法建立骨质疏松绵羊后将每只绵羊的腰椎（L1-6）随机分入三个不同的置钉组。使用相同的方法制备钉道后,普通椎弓根螺钉（CPS）组：经椎弓根向椎体内拧入CPS;PMMA-PS组：向制备好的钉道内注入1.0 m L的PMMA后拧入CPS;EPS组：直接经椎弓根向椎体内拧入EPS。术后6周和12周处死绵羊,经硬组织切片及染色后行组织学观察。结果组织学观察表明,在术后6周和12周,CPS组和EPS组中骨小梁直接与螺钉接触,形成了＂螺钉-骨质＂界面。PMMA-PS组中PMMA包裹螺钉,阻碍了螺钉与骨小梁的直接接触,形成了＂螺钉-PMMA-骨质＂界面,EPS组螺钉的前端明显膨胀形成了一个＂爪状＂结构,挤压并显著改善了局部的骨质条件。从术后6周到12周,CPS组和PMMA-PS组中螺钉周围的骨质条件无明显变化,PMMA无明显降解吸收,PMMA组中形成了二次界面,然而,术后12周EPS前端周围的骨质情况和钉道界面均明显优于术后6周。结论在骨质疏松绵羊腰椎内,术后早期EPS通过螺钉前段的膨胀挤压刺激周围骨小梁生长,显著改善了周围的骨质基础,随着螺钉膨胀部分持续挤压的刺激,螺钉前段周围的骨质条件在远期有进一步的显著改善,形成了良好的生物性界面,为螺钉的远期稳定提供了良好的骨质条件。

Objective To compare the interfaces of expansive pedicle screw （EPS） and polymethylmethacrylate-augmented pedicle screw（PMMA-PS） in osteoporotic sheep lumbar vertebrae through hard tissue sections and staining technique. Methods Six lumbar vertebrae（ L1-6 ） in each sheep were divided into three groups randomly（ two vertebrae with four pedicles in each group ） after establishment of osteoporosis sheep. In CPS group, CPS was inserted through the pilot hole into vertebral body with- out any augmentation. In PMMA-PS group,PMMA（ 1.0 mL） was injected into the pilot hole prior to the insertion of CPS. In EPS group, EPS was inserted through pedicle into vertebral body. The sheep were sacrificed and lumbar vertebrae（ L1-6 ） were harvested at the 6-week and 12-week post-operation,respectively. The histological observation was performed to evaluate the in- terfaeial properties. Results It was clearly demonstrated in histological observations. The bone trabeculae wrapped up screw directly forming ＂screw-bone＂ interface in both CPS and EPS groups at both 6-week and 12 week post-operation. PMMA sur- rounding the screw hampered the direct contact between bone and screw and formed＂ screw-PMMA-bone＂ interface in PMMA- PS group. The anterior part of EPS presented an obvious expansion in vertebral body and formed a clawlike structure, which pressing the surrounding bone trabeeulae and significantly improving the local bone condition （amount and density）. From 6- week to 12-week post-operation, there was no visual difference in bone condition（ amount and density）around screw in both CPS and PMMA-PS groups. PMMA was found remaining around screw without any degradation and absorption,which led to the second non-biological interface in PMMA-PS group. Nevertheless ,bone condition（ amount and density） around expanding part of EPS at 12 week were significantly improved compared with that at 6-week forming the good＂ screw-bone＂ interface. Conclusion EPS improve the bone condition around the anterior part of screw through expanding compression in early term in osteoporotic sheep lumbar vertebrae. Based on the stress stimulation from the continuous compression of anterior part of EPS, there is a significant improvement on the local bone condition in long term and form a good biological interface, which providing the good bone condition for the long-term stability.