Spoon C E, Wayne J S
Departments of Biomedical Engineering and Orthopaedic Surgery, Virginia Commonwealth University, Richmond, VA 23298-0694, USA.
Comput Methods Biomech Biomed Engin. 2004 Feb;7(1):17-23. doi: 10.1080/10255840410001653087.
Indentation tests are commonly used to determine the mechanical behaviour of articular cartilage with varying properties, thickness, and geometry. This investigation evaluated the effect of changing geometric parameters on the properties determined from creep indentation tests. Finite element analyses simulated the indentation behaviour of two models, an excised cylindrical specimen of cartilage with either normal and repair qualities and an osteochondral defect represented as a cylindrical region of repair cartilage integrated with a surrounding layer of normal tissue. For each model, the ratios of indenter radius to cartilage height (a/h=0.5,1.5) and cartilage radius to indenter radius (r/a=2,5) were varied. The vertical displacement of the cartilage under the indenter obtained through finite element analysis was fitted to a numerical algorithm to determine the aggregate modulus, permeability, and Poisson's ratio. Indentation behaviours of cartilage specimens for either model with a/h=1.5 were not affected by r/a for values of 2 and 5. Aggregate modulus was not greatly affected by the geometric changes studied. Permeability was affected by changes in the ratio of specimen to indenter radii for a/h=0.5. These findings suggest that experimental configurations of excised cylindrical specimens, also representing osteochondral defects with no or unknown degree of integration, where the cartilage layer has a/h=0.5 should not have r/a values on the order of 2 for confidence in the mechanical properties determined. Indentation of osteochondral defects where the repair cartilage is fully integrated to the surrounding cartilage can be performed with confidence for all cases tested.
压痕试验通常用于确定具有不同特性、厚度和几何形状的关节软骨的力学行为。本研究评估了改变几何参数对通过蠕变压痕试验确定的特性的影响。有限元分析模拟了两个模型的压痕行为，一个是具有正常和修复质量的切除圆柱形软骨标本，另一个是作为与周围正常组织层整合的修复软骨圆柱形区域表示的骨软骨缺损。对于每个模型，压头半径与软骨高度的比值（a/h = 0.5, 1.5）以及软骨半径与压头半径的比值（r/a = 2, 5）都有所变化。通过有限元分析获得的压头下软骨的垂直位移拟合到一个数值算法中，以确定总模量、渗透率和泊松比。对于a/h = 1.5的任一模型，软骨标本的压痕行为不受r/a值为2和5的影响。总模量受所研究的几何变化影响不大。对于a/h = 0.5，渗透率受标本与压头半径比值变化的影响。这些发现表明，切除的圆柱形标本的实验配置，也代表无整合或整合程度未知的骨软骨缺损，其中软骨层a/h = 0.5时，为了对所确定的力学性能有信心，r/a值不应在2左右。对于所有测试案例，可以放心地对修复软骨与周围软骨完全整合的骨软骨缺损进行压痕试验。
