Urban R M, Jacobs J J, Sumner D R, Peters C L, Voss F R, Galante J O
Department of Orthopedic Surgery, Rush-Presbyterian-St. Luke's Medical Center, Chicago, Illinois 60612, USA.
J Bone Joint Surg Am. 1996 Jul;78(7):1068-81. doi: 10.2106/00004623-199607000-00012.
A histological study was performed of the bone-implant interface of fifteen titanium-alloy femoral stems with porous coating limited to three proximal areas that did not cover the full circumference of the device. The specimens were obtained at autopsy from ten cadavera at a mean of forty-six months (range, one to eighty-nine months) after the implant had been inserted without acrylic cement. The volume fraction of bone within the porous spaces (the percentage of the porous space that was filled with bone) and the extent of bone ingrowth (the percentage of the porous-coated surface covered with in-grown bone that was more than one-half fiber-diameter deep, as measured from the outer surface of the porous coating), were determined with histomorphometric methods. Eleven of the fifteen stems had bone within the porous coating that was in continuity with the surrounding medullary bone. The mean volume fraction of bone ingrowth in these specimens was 26.9 per cent (range, 12.2 to 61.0 per cent), and the mean extent of bone ingrowth was 64.3 per cent (range, 28.6 to 95.2 per cent). Both of these parameters increased with time. In the other four stems, the bone lacked continuity with the surrounding trabecular bed. Two of these stems had a limited amount of bone within the porous coating, and two stems (from one patient) had no bone ingrowth. Periprosthetic membranes surrounded by a shell of trabecular bone covered the uncoated surfaces of the stems. The membranes of implants that had been in situ for eight months or more demonstrated polyethylene wear debris, and other particles generated at the level of the joint, within histiocytes throughout the length of the femoral stem.
The findings in this study are relevant to the utilization and mechanisms of failure of femoral stems inserted without cement. Bone ingrowth and the resulting stability of the implant can be achieved with porous-coated stems. However, the extent of the surface that is porous-coated must be sufficient to prevent trabecular fracture as a secondary mechanism of loosening. Interruptions in the circumferential extent of the porous surface are associated with the formation of periprosthetic membranes, which provide a pathway for migration of particulate wear and corrosion products to the distal part of the stem. A circumferential coating may retard the access of particles and thus decrease the possibility of diaphyseal osteolysis.
对15个钛合金股骨柄的骨-植入物界面进行了组织学研究，这些股骨柄的多孔涂层仅限于三个近端区域，未覆盖装置的整个圆周。标本取自10具尸体的尸检，平均在植入物无骨水泥植入后46个月（范围1至89个月）。采用组织形态计量学方法测定多孔空间内的骨体积分数（多孔空间中被骨填充的百分比）和骨长入程度（从多孔涂层外表面测量，被长入骨覆盖且深度超过纤维直径一半的多孔涂层表面的百分比）。15个股骨柄中有11个在多孔涂层内有与周围髓质骨连续的骨。这些标本中骨长入的平均体积分数为26.9%（范围12.2%至61.0%），骨长入的平均程度为64.3%（范围28.6%至95.2%）。这两个参数均随时间增加。在另外4个股骨柄中，骨与周围小梁床缺乏连续性。其中2个股骨柄在多孔涂层内骨量有限，2个股骨柄（来自1名患者）无骨长入。由小梁骨壳包围的假体周围膜覆盖了股骨柄的未涂层表面。在位8个月或更长时间的植入物的膜显示有聚乙烯磨损碎屑以及在关节水平产生的其他颗粒，这些颗粒存在于整个股骨柄长度的组织细胞内。
本研究结果与无骨水泥植入的股骨柄的使用及失效机制相关。多孔涂层股骨柄可实现骨长入及植入物由此产生的稳定性。然而，多孔涂层表面的范围必须足够以防止小梁骨折作为松动的继发机制。多孔表面圆周范围的中断与假体周围膜的形成相关，假体周围膜为颗粒磨损和腐蚀产物向股骨柄远端迁移提供了途径。圆周涂层可能会阻碍颗粒进入，从而降低骨干骨溶解的可能性。
