Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, 2500 University Drive N.W. Alberta, Canada.
J Biomech. 2011 Mar 15;44(5):930-4. doi: 10.1016/j.jbiomech.2010.11.031. Epub 2010 Dec 9.
Work relating the mechanical states of articular cartilage chondrocytes to their biosynthetic responses is based on measurements in isolated cells or cells in explant samples removed from their natural in situ environment. Neither the mechanics nor the associated biological responses of chondrocytes have ever been studied in cartilage within a joint of a live animal, and no such measurements have ever been performed using physiologically relevant joint loading through muscular contractions. The purpose of this study was to design and apply a method to study the mechanics of chondrocytes in the exposed but fully intact knee of live animals, which was loaded near-physiologically through muscular contraction. In order to achieve this purpose, we developed an accurate and reliable method based on two-photon laser excitation microscopy. Near-physiological knee joint loading was achieved through controlled electrical activation of the knee extensor muscles that compress the articulating surfaces of the femur, tibia and patella. Accuracy of the system was assessed by inserting micro-beads of known dimensions into the articular cartilage of the mouse knee and comparing the measured volumes and diameters in the principal directions with known values of the beads. Accuracy was best in the plane perpendicular to the optical axis (average error = 1%) while it was slightly worse, but still excellent, along the optical axis (average error = 3%). Reliability of cell volume and shape measurements was 0.5% on average, and 2.9% in the worst-case-scenario. Pilot measurements of chondrocyte deformations upon sub-maximal muscular loading causing a mean articular contact pressure of 1.9 ± 0.2 MPa showed an "instantaneous" decrease in cell height (17 ± 4.5%) and loss of cell volume (22.3 ± 2.4%) that took minutes to recover upon deactivation of the knee extensor muscles.
研究关节软骨细胞的机械状态与其生物合成反应的关系，是基于对分离细胞或从其自然原位环境中取出的组织样本中的细胞进行测量。无论是软骨细胞的力学特性还是相关的生物学反应，都从未在活体动物关节的软骨中进行过研究，也从未使用肌肉收缩产生的生理相关关节负荷进行过此类测量。本研究旨在设计并应用一种方法，研究活体动物暴露但完整的膝关节中软骨细胞的力学特性，该方法通过肌肉收缩实现近生理负荷。为了达到这个目的，我们开发了一种基于双光子激光激发显微镜的精确可靠的方法。通过对膝关节伸肌进行受控电刺激，实现了近生理的膝关节加载，从而压缩股骨、胫骨和髌骨的关节面。该系统的准确性通过将已知尺寸的微珠插入小鼠膝关节的关节软骨中进行评估，并将测量的体积和主方向上的直径与珠的已知值进行比较。垂直于光轴的平面上的准确性最好（平均误差=1%），而沿着光轴的准确性略差，但仍非常出色（平均误差=3%）。细胞体积和形状测量的可靠性平均为 0.5%，在最坏情况下为 2.9%。在亚最大肌肉负荷下测量软骨细胞变形的初步结果表明，当关节接触压力平均为 1.9±0.2MPa 时，细胞高度（17±4.5%）和细胞体积（22.3±2.4%）会“瞬间”下降，当膝关节伸肌失活后，需要几分钟才能恢复。
