Engh C A, O'Connor D, Jasty M, McGovern T F, Bobyn J D, Harris W H
Anderson Orthopaedic Research Institute, Arlington, Virginia 22206.
Clin Orthop Relat Res. 1992 Dec(285):13-29.
Fourteen femora containing porous-coated anatomic medullary locking (AML) femoral prostheses were retrieved from 12 patients at autopsy. Clinical roentgenograms in 13 femora showed bone remodeling changes, indicating that the implants were fixed by osseointegration. Under simulated physiologic loading, micromotion between the implant and the bone was measured using electrical displacement transducers connected to the implant and to the adjacent cortex. The micromotion between the implants at the areas of porous coating and the adjacent cortex in the one case of failed bone ingrowth measured 150 microns. Maximum relative motion between the cortex and the implant in the areas of porous coating for the 13 cases showing signs of bone ingrowth was 40 microns, and this was completely elastic relative displacement. With all implants, the micromotion between the cortex and the stem was always greatest over the uncoated portion of the stem. Four of the implants were proximally porous coated. With these, the micromotion was greater over the uncoated areas than with more extensively coated stems and was always greatest at the uncoated tip of the prosthesis. The amount of micromotion was directly related to the extent of porous coating on the implant. Maximum tip motion for the proximally coated implants was 210 micra, whereas for the fully porous-coated implants, it was 40 microns. In nine of the autopsies, the contralateral normal femur was obtained in addition to the femur containing the AML (the in vivo remodeled femur). These were used for comparative studies of strain shielding and femoral remodeling. Cortical strains were measured in the in vivo remodeled femora and were compared with measurements made in the contralateral normal femora before and following implantation of a stem identical to that present on the clinically treated side. The data showed major strain reductions in all the postmortem implanted normal femora. Comparison of the strain data from the postmortem implanted normal femora with those from the in vivo remodeled femora clearly indicated that extensive bone remodeling did not result in restoration of cortical strain levels anywhere near normal. Strain shielding continued to exist in all of the remodeled specimens, even up to 7.5 years after surgery. This strain shielding was associated with bone remodeling changes that resulted in regional reductions in bone mineral content that ranged from 7% to 78%. These observations are unique, important, and valuable in defining the in vivo function and clinical behavior of this type of porous-coated femoral component.
从12例患者尸检中获取了14个股骨，这些股骨植入了多孔涂层解剖型髓内锁定（AML）股骨假体。13个股骨的临床X线片显示有骨重塑变化，表明植入物通过骨整合固定。在模拟生理负荷下，使用连接到植入物和相邻皮质的电位移传感器测量植入物与骨之间的微动。在一例骨长入失败的病例中，多孔涂层区域的植入物与相邻皮质之间的微动测量为150微米。在13例显示骨长入迹象的病例中，多孔涂层区域皮质与植入物之间的最大相对运动为40微米，这是完全弹性的相对位移。对于所有植入物，皮质与柄之间的微动在柄的未涂层部分始终最大。其中4个植入物近端为多孔涂层。对于这些植入物，未涂层区域的微动比涂层更广泛的柄更大，并且在假体的未涂层尖端始终最大。微动的量与植入物上多孔涂层的范围直接相关。近端涂层植入物的最大尖端运动为210微米，而对于完全多孔涂层植入物，为40微米。在9例尸检中，除了含有AML的股骨（体内重塑股骨）外，还获取了对侧正常股骨。这些用于应变屏蔽和股骨重塑的比较研究。在体内重塑的股骨中测量皮质应变，并与在植入与临床治疗侧相同柄之前和之后对侧正常股骨中的测量值进行比较。数据显示所有死后植入的正常股骨中应变均大幅降低。将死后植入的正常股骨的应变数据与体内重塑股骨的应变数据进行比较清楚地表明，广泛的骨重塑并未导致皮质应变水平恢复到接近正常的水平。应变屏蔽在所有重塑标本中持续存在，甚至在手术后长达7.5年。这种应变屏蔽与骨重塑变化相关，导致骨矿物质含量区域减少7%至至78%。这些观察结果对于定义这种类型的多孔涂层股骨部件的体内功能和临床行为具有独特、重要和有价值的意义。
