Harman Melinda K, Schmitt Sabine, Rössing Sven, Banks Scott A, Sharf Hans-Peter, Viceconti Marco, Hodge W Andrew
Medical Technology Lab, Rizzoli Orthopaedic Institute, Via di Barbiano 1/10, Bologna, Italy.
Clin Biomech (Bristol). 2010 Jul;25(6):570-5. doi: 10.1016/j.clinbiomech.2010.03.013. Epub 2010 May 8.
Deviations from nominal alignment of unicondylar knee replacements impact knee biomechanics, including the load and stress distribution at the articular contact surfaces. This study characterizes relationships between the biomechanical environment, distinguished by progressive changes in alignment and fixation, and articular damage and deformation in a consecutive series of retrieved unicondylar knee replacements.
Twenty seven fixed-bearing, non-conforming unicondylar knee replacements of one design were retrieved after 2 to 13 years of in vivo function. The in vivo biomechanical environment was characterized by grading component migration measured from full-length radiographs and grading component fixation based on intraoperative manual palpation. Articular damage patterns and linear deformation on the polyethylene inserts were measured using optical photogrammetry and contact point digitization.
Articular damage patterns and surface deformation on the explanted polyethylene inserts corresponded to progressive changes in component alignment and fixation. Component migration produced higher deformation rates, whereas loosening contributed to larger damage areas but lower deformation rates. Migration and loosening of the femoral component, but not the tibial component, were factors contributing to large regions of abrasion concentrated on the articular periphery.
Classifying component migration and fixation at revision proved useful for distinguishing common biomechanical conditions associated with the varied polyethylene damage patterns and linear deformation for this fixed-bearing, non-conforming design. Pre-clinical evaluations of unicondylar knee replacements that are capable of reproducing variations in clinical alignment and predicting the observed wear mechanisms are necessary to better understand the impact of knee biomechanics and design on unicondylar knee replacement longevity.
单髁膝关节置换假体的标称对线偏差会影响膝关节生物力学，包括关节接触面的负荷和应力分布。本研究描述了在一系列连续回收的单髁膝关节置换假体中，以对线和固定的渐进性变化为特征的生物力学环境与关节损伤和变形之间的关系。
在体内发挥功能2至13年后，回收了27个一种设计的固定平台、非标准单髁膝关节置换假体。通过对全长X线片测量的假体移位进行分级以及基于术中手动触诊对假体固定进行分级，来描述体内生物力学环境。使用光学摄影测量法和接触点数字化测量聚乙烯衬垫上的关节损伤模式和线性变形。
取出的聚乙烯衬垫上的关节损伤模式和表面变形与假体对线和固定的渐进性变化相对应。假体移位产生更高的变形率，而松动则导致更大的损伤面积，但变形率较低。股骨假体而非胫骨假体的移位和松动是导致集中在关节周边的大面积磨损的因素。
在翻修时对假体移位和固定进行分类，对于区分与这种固定平台、非标准设计中聚乙烯损伤模式和线性变形各异相关的常见生物力学状况很有用。能够再现临床对线变化并预测观察到的磨损机制的单髁膝关节置换假体的临床前评估，对于更好地理解膝关节生物力学和设计对单髁膝关节置换假体使用寿命的影响是必要的。
