Identification of Juxta-meniscus capsule and development of its augmentation method

Abstract

Meniscal tissue is composed of a fine dense framework of predominantly circumferentially oriented collagen fibers with few radially aligned fibers that binds circumferential fibers. This distinctive geometry and microstructure of meniscus is essential for the meniscus to function, allowing load transfer, shock absorption, and full conformity to occur whilst minimizing contact pressure This is achieved by creating a tensional radial displacement of generated forces through circumferential hoop tension dissipation. On the other hand, meniscus tear, especially root tear, or degenerative change of the joint accompanies the loss of hoop tension and may lead to meniscus extrusion. The microstructure and the role of the meniscus is well studied but those of the adjacent capsule that wraps the meniscus (peri-meniscal capsule) has not been described. Since menisco-capsular separation may not only cause clinical symptoms but also adversely affect knee biomechanics, it is plausible that peri-meniscal capsule also plays a role in the stability and function of the meniscus. In chapter Ⅰ: The goal of this study is to analyze the morphological and biomechanical characteristics of peri-meniscal capsule in knee joint thus establishing the roles of these tissues. A total of 10 human cadaver knees were used in this study. Medial meniscus and the adjacently surrounding joint capsules were harvested then sectioned both axially and coronally, followed by electron microscopy (SEM) analyses. The medial meniscus (anterior; middle; posterior) and the adjacent peri-meniscal capsules (superior; perioral) were biomechanically to assessed to ascertain the tensile modulus. Among the peri-meniscal capsules, the peripherally located capsules were morphologically different from the superiorly located capsules: The peripheral peri-meniscal capsule was thicker and showed circumferentially oriented fibers whereas the superior peri-meniscal capsule fibers were thinner and arranged in vertical orientation. The peripheral capsule also yielded significantly greater tensile modulus compared to the superior capsule biomechanically. Depending on its anatomical location, the peri-meniscal capsule consists of fibers of varying orientations. This may be important in maintaining the circumferential hoop tension of the meniscus especially in the presence of circumferentially-oriented and thick peripheral capsule fibers, which coincidentally has higher tensile modulus. In chapter Ⅱ: Meniscus functions while maintaining hoop stress and fails from its original place by a tear or degenerative change. This failure often happens medially, more specifically root area, leading to extrusion of the meniscus. Extrusion of meniscus results in increased tibiofemoral contact pressures, accelerating joint cartilage damage and the progression of osteoarthritis. Therefore, the eventual goal of the meniscus tear is to restore meniscus hoop stress and to prevent the extrusion. However, there are currently no clinical treatment options that target extrusion, so we assumed that it would be possible to restore the function of meniscus when we prevent meniscal extrusion and maintain its original position after the meniscus tear. A total of 28 rabbits were divided into four groups (A: normal, B: root tear, C: root tear + repair, D: root tear + ring augmentation). For ring augmentation, wire suture was passed circumferentially to the periphery of the meniscus, and each of the two suture ends was passed through the anterior and posterior insertional root and fixed by post-time. At 4 and 8 weeks after surgery, the degree of meniscus extrusion was analyzed using micro-CT and tibiofemoral joint contact pressure was measured accordingly. Ring augmentation group resulted in significantly less meniscal extrusion compared to the root group and repair group. Tibiofemoral joint contact pressure was also significantly lower in the ring augmentation group. Circumferential ring augmentation procedure of the meniscus reduces the degree of meniscus extrusion, and it also restores meniscal function by lowering tibiofemoral joint contact pressure, which may eventually contribute to the prevention of the progression of knee osteoarthritis.