Raimondi M T, Sassi R, Pietrabissa R
Laboratory of Biological Structure Mechanics, Dipartimento di Bioingegneria, Politecnico di Milano, Milan, Italy.
Proc Inst Mech Eng H. 2000;214(6):577-87. doi: 10.1243/0954411001535606.
Studies on retrieved hip prostheses are currently performed in order to assess the wear mechanisms and the overall wear rate of such artificial joints. Several reported studies on the survival of artificial hips have been based on the measurement of the amount of worn material directly on retrieved acetabular cups. The estimation of the change in volume, V, of the cup cavity is particularly difficult in the case of slight wear due to several factors of which the most critical is the lack of information on the unworn geometry of the cup. This paper presents a new measuring technique, which is described in detail and has been applied to estimate the wear of 65 acetabular cups harvested from revised hip arthroplasty. The coordinate data of several points on the articular surface are sampled using a coordinate measuring machine (CMM). The value of V is calculated mathematically from the measurements by using the hypothesis that the actual shape of both slightly worn and highly worn surfaces has a small departure from a truly spherical shape. The wear volume is estimated with reasonable accuracy mainly on those cups showing penetration depths greater than 0.2 mm, corresponding to an amount of wear greater than 100 mm3 for a 32 mm cup. The uncertainty in the results is estimated for each cup. The repeatability of the technique is studied for a case showing very slight wear. The advantages, disadvantages and limitations of the method are presented and discussed.
目前开展了关于取出的髋关节假体的研究，以评估此类人工关节的磨损机制和总体磨损率。几项已报道的关于人工髋关节存活率的研究是基于直接测量取出的髋臼杯上磨损材料的量。由于多种因素，在轻微磨损的情况下，估计杯腔体积V的变化尤为困难，其中最关键的因素是缺乏关于未磨损杯几何形状的信息。本文介绍了一种新的测量技术，该技术将被详细描述，并已应用于估计从翻修髋关节置换术中取出的65个髋臼杯的磨损情况。使用坐标测量机（CMM）对关节表面上几个点的坐标数据进行采样。通过假设轻微磨损和高度磨损表面的实际形状与真正的球形有微小偏差，根据测量结果通过数学计算得出V的值。主要针对那些穿透深度大于0.2毫米的杯，估计磨损体积，对于一个32毫米的杯，这相当于磨损量大于100立方毫米。对每个杯估计结果的不确定性。针对一个磨损非常轻微的案例研究了该技术的可重复性。介绍并讨论了该方法的优点、缺点和局限性。
