In vitro Method to Quantify and Visualize Volumetric Wear in Meniscus Subjected to Joint Loading Using a 3D Optical Scanner

Abstract

The menisci are fibrocartilaginous soft tissues that act to absorb and distribute load across the surface of the knee joint. As a result of mechanical wear and large repetitive loading, meniscus tissue can begin to breakdown, or degenerate. Meniscus degeneration increases the risk of tearing, weakened tissue integrity, and the progression of osteoarthritis. Therefore, it is imperative to understand the wear behavior of whole human meniscus to identify conditions that may significantly increase the risk of degeneration. The objective of this study is to develop and validate an in vitro methodology for characterizing volumetric wear behavior in whole human meniscus using a 3D optical scanning system. This study was done in three parts. Part I and II consisted of assessing the accuracy and repeatability of the proposed methodology for meniscus tissue. Two surrogate models were developed for this purpose: (1) Simple Surrogate: Geometric Blocks and (2) Complex Surrogate: Menisci & Tibia Replicas. Part III utilized the method to quantify wear in whole human meniscus subjected to physiological loading conditions. One fresh-frozen cadaveric knee joint was potted in a custom designed and built knee simulator and subjected to four loading stages of 250,000 cycles. A 3D optical scanner was used to generate 3D renderings for pre- and post-wear conditions for both surrogates and human meniscus. An open-source software, CloudCompare, was then used to computationally evaluate volume loss. For the surrogate models, the process was repeated at varying wear depths, and the percentage error between real-life measured volumes and CloudCompare calculated volumes was determined. The human meniscus followed the same scanning procedure for pre- and post-wear; however, post-wear volume was recorded following each loading stage. Results from the simple surrogate model showed that the method was capable of measuring wear with < 2% error when detecting volumetric changes of 1.08 cm3 ; however, as defect depth decreased, the absolute mean percentage error increased (p < 0.001). The complex surrogate model showed significant difference when measuring wear in the lateral and medial meniscus (p < 0.05) with percentage errors of less than 7.9% when detecting volumetric changes of 0.4 cm3. The results obtained from whole human meniscus testing indicate that with an increase in loading cycles, a higher degree of meniscal wear and deformation is present. For the first time, this study provides a methodology to identify volumetric loss due to wear behavior in whole human meniscus. This is also the first study to provide comprehensive visualization and identification of global defects within the meniscus tissue. Results of this study have the potential to help identify the physical and biochemical factors that lead to meniscus degeneration thereby advancing fundamental knowledge of the etiology of degenerative wear within articulating soft tissue.