Speirs Andrew D, Heller Markus O, Taylor William R, Duda Georg N, Perka Carsten
Center for Musculoskeletal Surgery, Charité--Universitätsmedizin Berlin, Augustenburger Platz 1, D-13353 Berlin, Germany.
Clin Biomech (Bristol). 2007 May;22(4):431-9. doi: 10.1016/j.clinbiomech.2006.12.003. Epub 2007 Feb 1.
Short-stemmed hip implants were introduced to conserve proximal bone mass and may facilitate the use of minimally invasive surgery, in which smaller incisions limit access to the joint. This limited access may increase the risk of surgical mal-positioning of the implant, however the sensitivity of femoral loading to such mal-positioning of a short-stemmed implant has not been studied.
Finite element models were developed of a femur and a short-stemmed implant positioned to reproduce the intact hip centre, as well as with the implant placed in increased anteversion or offset. The effect of these surgical variables on femoral loading was examined for walking and stair climbing using loads from a validated musculoskeletal model. Results of the implanted models were compared with an intact model to evaluate stress shielding.
Implant position had little influence on cortical strains along the length of the diaphysis, although strains decreased by up to 95% at the neck resection level compared to the intact femur. In the proximal Gruen zones I and VII strain energy density among the implanted models varied by up to 0.4 kJ/m(3) (28%) and 0.6 kJ/m(3) (24%) under walking and stair climbing, respectively. All implanted models showed characteristic proximal stress shielding, indicated by a decrease in strain energy density of up to 5.4 kJ/m(3) (69%) compared to the intact femur.
Small changes in stem placement would likely have little influence on the internal loading of the femur after bone ingrowth has been achieved, however a reduction in strain energy density and therefore stress shielding was seen even for a short-stemmed implant, which may have consequences for longer-term bone remodelling.
短柄髋关节植入物被引入以保留近端骨量，并可能便于使用微创手术，因为较小的切口限制了进入关节的通道。然而，这种有限的通道可能会增加植入物手术位置不当的风险，不过短柄植入物位置不当对股骨负荷的敏感性尚未得到研究。
建立了股骨和短柄植入物的有限元模型，植入物的位置可重现完整的髋关节中心，也可将植入物置于增加的前倾角或偏移量的位置。使用经过验证的肌肉骨骼模型的负荷，研究了这些手术变量对步行和爬楼梯时股骨负荷的影响。将植入模型的结果与完整模型进行比较，以评估应力遮挡。
植入物位置对骨干长度上的皮质应变影响很小，尽管与完整股骨相比，在颈切除水平处应变降低了高达95%。在近端Gruen I区和VII区，步行和爬楼梯时植入模型中的应变能密度分别变化高达0.4 kJ/m³（28%）和0.6 kJ/m³（24%）。所有植入模型均显示出典型的近端应力遮挡，与完整股骨相比，应变能密度降低了高达5.4 kJ/m³（69%）。
在骨长入完成后，柄部位置的微小变化可能对股骨的内部负荷影响不大，然而，即使是短柄植入物也出现了应变能密度降低以及应力遮挡，这可能会对长期的骨重塑产生影响。
