Räsänen Lasse P, Tanska Petri, Zbýň Štefan, van Donkelaar Corrinus C, Trattnig Siegfried, Nieminen Miika T, Korhonen Rami K
Department of Applied Physics, University of Eastern Finland, Kuopio, Finland; Diagnostic Imaging Center, Kuopio University Hospital, Kuopio, Finland.
Department of Applied Physics, University of Eastern Finland, Kuopio, Finland.
J Biomech. 2017 Aug 16;61:34-44. doi: 10.1016/j.jbiomech.2017.06.041. Epub 2017 Jul 6.
The effect of swelling of articular cartilage, caused by the fixed charge density (FCD) of proteoglycans, has not been demonstrated on knee joint mechanics during simulated walking before. In this study, the influence of the depth-wise variation of FCD was investigated on the internal collagen fibril strains and the mechanical response of the knee joint cartilage during gait using finite element (FE) analysis. The FCD distribution of tibial cartilage was implemented from sodium (Na) MRI into a 3-D FE-model of the knee joint ("Healthy model"). For comparison, models with decreased FCD values were created according to the decrease in FCD associated with the progression of osteoarthritis (OA) ("Early OA" and "Advanced OA" models). In addition, a model without FCD was created ("No FCD" model). The effect of FCD was studied with five different collagen fibril network moduli of cartilage. Using the reference fibril network moduli, the decrease in FCD from "Healthy model" to "Early OA" and "Advanced OA" models resulted in increased axial strains (by +2 and +6%) and decreased fibril strains (by -3 and -13%) throughout the stance, respectively, calculated as mean values through cartilage depth in the tibiofemoral contact regions. Correspondingly, compared to the "Healthy model", the removal of the FCD altogether in "NoFCD model" resulted in increased mean axial strains by +16% and decreased mean fibril strains by -24%. This effect was amplified as the fibril network moduli were decreased by 80% from the reference. Then mean axial strains increased by +6, +19 and +49% and mean fibril strains decreased by -9, -20 and -32%, respectively. Our results suggest that the FCD in articular cartilage has influence on cartilage responses in the knee during walking. Furthermore, the FCD is suggested to have larger impact on cartilage function as the collagen network degenerates e.g. in OA.
蛋白聚糖的固定电荷密度（FCD）所引起的关节软骨肿胀对模拟行走过程中膝关节力学的影响，此前尚未得到证实。在本研究中，利用有限元（FE）分析，研究了FCD的深度变化对步态期间膝关节软骨内部胶原纤维应变及力学响应的影响。将来自钠（Na）MRI的胫骨软骨FCD分布应用于膝关节的三维有限元模型（“健康模型”）。为作比较，根据与骨关节炎（OA）进展相关的FCD降低情况创建了FCD值降低的模型（“早期OA”和“晚期OA”模型）。此外，还创建了一个无FCD的模型（“无FCD”模型）。使用五种不同的软骨胶原纤维网络模量研究了FCD的影响。以参考纤维网络模量为例，从“健康模型”到“早期OA”和“晚期OA”模型，FCD的降低分别导致整个站立期轴向应变增加（分别增加+2%和+6%）和纤维应变降低（分别降低-3%和-13%），这些应变是通过胫股接触区域软骨深度的平均值计算得出的。相应地，与“健康模型”相比，“无FCD模型”中完全去除FCD导致平均轴向应变增加+16%，平均纤维应变降低-24%。当纤维网络模量从参考值降低80%时，这种效应会放大。此时，平均轴向应变分别增加+6%、+19%和+49%，平均纤维应变分别降低-9%、-20%和-32%。我们的结果表明，关节软骨中的FCD对行走过程中膝关节的软骨反应有影响。此外，随着胶原网络退化，如在OA中，FCD对软骨功能的影响可能更大。
