Augat P, Claes L, Hanselmann K F, Suger G, Fleischmann W
Abteilung Unfallchirurgische Forschung und Biomechanik, University of Ulm, Germany.
J Appl Biomater. 1995 Summer;6(2):99-104. doi: 10.1002/jab.770060203.
A major problem in fracture treatment by external fixation is screw loosening, which often results in reduced stability and can lead to prolonged treatment. A load-carrying experiment was conducted to determine whether coating implants with bioactive hydroxyapatite (HA) increases screw stability. Twelve HA-coated ASIF screws with 3 different macroporosities were inserted in 12 sheep that had already been fitted with a 6-pin external fixator for the treatment of a tibial osteotomy. The same number of uncoated polished steel screws served as controls. Although initial stability was not different for HA-coated screws, average removal torque after a 9-week implantation period increased with increasing macroporosity of the HA coating (p < .002). Instability of some screws was accompanied by histologic findings of cartilagenous tissue and proliferation of periosteal callus. Near the threads in the tibial cortex and in the shaft area of the screw were seen large numbers of HA particles that had been sheared off during implantation as well as during screw removal because of high contact forces between the HA coating and bone. Particulate debris of HA particles as well as the release of small bone fragments during explanation is likely to be unavoidable since HA adherence to bone is greater than adherence to steel after several weeks of implantation.
外固定治疗骨折的一个主要问题是螺钉松动，这常常导致稳定性下降并可能延长治疗时间。进行了一项承载实验，以确定用生物活性羟基磷灰石（HA）涂层植入物是否能提高螺钉稳定性。将12枚具有3种不同大孔隙率的HA涂层ASIF螺钉插入12只已安装6针外固定器用于治疗胫骨截骨术的绵羊体内。相同数量的未涂层抛光钢螺钉作为对照。虽然HA涂层螺钉的初始稳定性没有差异，但在9周植入期后的平均拔除扭矩随着HA涂层大孔隙率的增加而增加（p < .002）。一些螺钉的不稳定伴随着软骨组织和骨膜骨痂增生的组织学表现。在胫骨皮质的螺纹附近以及螺钉的杆部区域，可以看到大量在植入过程中以及由于HA涂层与骨之间的高接触力在螺钉取出过程中被剪切下来的HA颗粒。由于植入几周后HA与骨的附着力大于与钢的附着力，HA颗粒的颗粒碎片以及在取出过程中小骨碎片的释放可能是不可避免的。
