Ramamurti B S, Bragdon C R, O'Connor D O, Lowenstein J D, Jasty M, Estok D M, Harris W H
Orthopaedic Biomechanics Laboratory, Massachusetts General Hospital, Boston 02114, USA.
J Arthroplasty. 1996 Oct;11(7):845-52. doi: 10.1016/s0883-5403(96)80185-9.
Wear of ultrahigh-molecular-weight polyethylene and the subsequent lytic response to the particulate wear debris are the dominant problems in total joint arthroplasty surgery. Wear testing apparatus can play a vital role in the in vitro evaluation of the many factors involved in wear, such as head size, surface roughness, materials for the head, and new materials for the socket. Wear of ultrahigh-molecular-weight polyethylene may be influenced by the wear path. For the related polymer, high-density polyethylene, the wear path is critical to wear magnitude. What is the actual path taken by a single point (or by multiple representative points) on the femoral head of a total hip arthroplasty as it passes through the gait cycle? The goal of this computer simulation study was to trace the paths of specific points on the femoral head as they moved against the polyethylene cup during a single cycle of normal gait to illustrate the motions occurring at the intraarticular surface of the hip joint. This study also yielded unusual data on the "distance traversed" by these points during a single gait cycle. It was found that there was not one path, but rather there were many, and the paths varied widely in both shape and length depending on the location on the femoral head. Moreover, the differences in excursion and direction at different sites during the loaded phase were great. In addition, distances traveled by different points on the femoral head of any given size varied by a factor greater than 2. Most of the points traced quasielliptical paths. This automatically means that the paths of neighboring points cross each other, creating multidirectional shear forces on the acetabular cup surface which may be important in the localization and extent of wear. The plots of traces of the points derived from this study can serve as benchmarks for the ability of hip simulators to reproduce the actual distances and paths of travel of individual points on the femoral head.
超高分子量聚乙烯的磨损以及随后对颗粒磨损碎屑的溶解反应是全关节置换手术中的主要问题。磨损测试设备在体外评估磨损涉及的诸多因素（如头部尺寸、表面粗糙度、头部材料以及髋臼的新材料）方面可发挥至关重要的作用。超高分子量聚乙烯的磨损可能受磨损路径影响。对于相关聚合物高密度聚乙烯而言，磨损路径对磨损程度至关重要。在全髋关节置换术中，股骨头单个点（或多个代表性点）在步态周期中实际走过的路径是怎样的呢？本计算机模拟研究的目的是追踪股骨头特定点在正常步态单个周期内相对于聚乙烯杯运动时的路径，以阐明髋关节关节内表面发生的运动。这项研究还得出了这些点在单个步态周期内“走过的距离”的不同寻常的数据。研究发现，并非只有一条路径，而是有许多条路径，并且路径的形状和长度因股骨头位置不同而有很大差异。此外，在负重阶段不同部位的偏移和方向差异很大。另外，任何给定尺寸的股骨头不同点走过的距离相差超过两倍。大多数点的轨迹呈准椭圆形。这自然而然地意味着相邻点的路径相互交叉，在髋臼杯表面产生多方向剪切力，这可能对磨损的定位和程度具有重要意义。本研究得出的点的轨迹图可作为髋关节模拟器再现股骨头单个点实际行进距离和路径能力的基准。
