Chen Chun-Ming, Tsai Wen-Chi, Lin Shang-Chih, Tseng Ching-Shiow
Graduate Institute of Biomedical Engineering, National Taiwan University of Science and Technology, No, 43, Sec, 4, Keelung Rd, Taipei 106, Taiwan.
BMC Musculoskelet Disord. 2014 Sep 26;15:312. doi: 10.1186/1471-2474-15-312.
Despite improvements in shape, material, and coating for hip stem, both stress shielding and aseptic loosening have been the major drawbacks of stemmed hip arthroplasty. Some nonstemmed systems were developed to avoid rasping off the intramedullary canal and evacuating the bone marrow due to stem insertion.
In this study, the finite-element models of one intact, one stemmed, and two nonstemmed femora with minimal removal of the healthy neck were investigated to evaluate their biomechanical effects. The resurfacing (ball-shaped) and fitting (neck-shaped) systems were respectively selected as the representative of the ready- and custom-made nonstemmed implants. The stress distribution and interface micromotion were selected as the comparison indices.
The results showed that stress distributions of the two nonstemmed femora are consistently more similar to the intact femur than the stemmed one. Around the proximal femur, the stem definitely induces the stress-shielding phenomenon of its counterparts. The fitting system with the anatomy-shaped cup can make intimate contact with the neck cortex and reduce the bone-cup micromotion and the implant stress. Comparatively, the reamed femoral head provides weaker support to the resurfacing cup causing higher interfacial micromotion.
The reserved femoral neck could act as the load-transferring medium from the acetabular cup, femoral neck, to the diaphysial bone, thus depressing the stress-shielding effect below the neck region. If the hip-cup construct can be definitely stabilized, the nonstemmed design could be an alternative of hip arthroplasty for the younger or the specific patients with the disease limited only to the femoral head.
尽管髋关节柄在形状、材料和涂层方面有所改进，但应力遮挡和无菌性松动一直是带柄髋关节置换术的主要缺点。一些无柄系统被开发出来，以避免因柄的插入而刮除髓腔并清空骨髓。
在本研究中，研究了一个完整股骨、一个带柄股骨和两个切除健康股骨颈最少的无柄股骨的有限元模型，以评估它们的生物力学效应。分别选择表面置换（球形）和贴合（颈形）系统作为现成和定制无柄植入物的代表。选择应力分布和界面微动作为比较指标。
结果表明，与带柄股骨相比，两个无柄股骨的应力分布始终与完整股骨更相似。在股骨近端周围，柄肯定会引起其对应部位的应力遮挡现象。带有解剖形状髋臼杯的贴合系统可以与颈皮质紧密接触，减少骨-杯微动和植入物应力。相比之下，扩孔的股骨头对表面置换杯的支撑较弱，导致更高的界面微动。
保留的股骨颈可以作为从髋臼杯、股骨颈到骨干骨的载荷传递介质，从而降低颈部区域以下的应力遮挡效应。如果髋关节杯结构能够得到明确稳定，无柄设计可能是年轻患者或仅股骨头患病的特定患者髋关节置换术的一种选择。
