Department of Mechanical Engineering, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
J Biomech. 2010 Feb 10;43(3):477-84. doi: 10.1016/j.jbiomech.2009.09.048. Epub 2009 Dec 11.
Strain shielding, a mechanical effect occurring in structures combining stiff with more flexible materials, is considered to lead to a reduction of density in bone surrounding the implant. This effect can be related to the weakness of the implant fixation, which can promote implant loosening. Several studies describe a significant decrease in postoperative bone mineral density adjacent to joint implants, which can compromise their long-term fixation. The aim of the present study was to quantify the strain shielding effect on the distal femur after patellofemoral arthroplasty. For this purpose three activities of daily living were considered: level walking, stair climbing and deep bending at different angles of knee flexion. To determine the strain shielding effect, cortical bone strains were measured experimentally with triaxial strain gauges in synthetic femurs before and after patellofemoral arthroplasty for each of the different daily activities. The results showed that the patellofemoral arthroplasty in general reduced the strains in the medial and distal regions of the femur when deep bending activity occurred, consequently, strain shielding in these regions, with strain decreases of -72.0% and -67.5% were measured. On the other side, higher values of strain were found in the anterior region after patellofemoral replacement for this activity with an increase of +182.0%. The occurrence of strain shielding seems to be more significant when the angle of knee flexion and applied load increases. Strain shielding and over-loading may have relevant effects on bone remodeling surrounding the patellofemoral implant, suggesting a potential effect of later bone resorption in the medial and distal femur regions in case of regular deep bending activity.
应变屏蔽是一种在结合了刚性和柔性材料的结构中发生的机械效应，被认为会导致植入物周围骨骼的密度降低。这种效应可能与植入物固定的松动有关，从而促进植入物松动。有几项研究描述了关节植入物附近术后骨密度的显著下降，这可能会影响其长期固定。本研究的目的是量化髌股关节置换术后对股骨远端的应变屏蔽效应。为此，考虑了三种日常生活活动：水平行走、爬楼梯和在不同膝关节弯曲角度下的深度弯曲。为了确定应变屏蔽效应，使用三轴应变计在髌股关节置换前后的合成股骨中实验测量了皮质骨应变，用于每种不同的日常活动。结果表明，髌股关节置换术通常会降低深度弯曲活动时股骨内侧和远端的应变，因此，这些区域的应变屏蔽效应测量值分别降低了-72.0%和-67.5%。另一方面，对于这种活动，在前部区域发现了更高的应变值，增加了+182.0%。当膝关节弯曲角度和施加的载荷增加时，应变屏蔽似乎更为显著。应变屏蔽和过载可能对髌股植入物周围的骨重塑产生相关影响，这表明在经常进行深度弯曲活动的情况下，内侧和远端股骨区域可能会出现骨吸收的潜在影响。
