Stiffness of meniscus tissue depends on tibio-femoral load and structural integrity of the meniscus root.

Development of meniscus replacements requires in-depth knowledge of the material properties and biomechanical behavior of the native meniscus. The compressive properties are of particular interest in this context, which are often assessed with indentation tests. However, those tests are usually done on isolated tissue specimens ex situ, which could have a significant impact on the results. It was, therefore, the goal of the study to assess the stiffness of the meniscus tissue in situ in porcine specimens and to compare it to that of artificial substitutes. Porcine knees (n = 8) were prepared such that the medial meniscus periphery was exposed and the knees could be mounted in a materials testing machine. The tissue stiffness was than measured on the meniscus periphery using a Shore-A durometer in (1) the unloaded knee, (2) with 500-N tibio-femoral compressive load, and (3) with 500-N tibio-femoral load and the posterior meniscus root detached. The stiffness of the meniscus tissue was significantly increased when tibio-femoral load was applied, while this effect was lost when the meniscus root was cut (average measurements on a 0-100 Shore-A durometer scale: group A, 33.8; group B, 58.4; and group C, 36.2). Polyurethane and collagen meniscus implants showed an inferior stiffness compared to the native meniscus. These findings might be relevant for the material choice in artificial meniscus replacements and the fixation of allografts. Biomechanical testing of isolated tissue specimens could underestimate the effective meniscus tissue stiffness compared to a physiological joint environment.