Relationship Between Meniscal Sample Swelling and the Compressive Properties of Bovine Menisci

The menisci are anisotropic hydrated connective tissues, situated in the tibiofemoral joint. The menisci transmit approximately 50% of the load across this joint [1, 2]. In this tissue, compression would only be experienced in the axial (vertical) direction, and as such, many studies have tested samples in the axial direction to determine the compressive properties [3–5]. The material behaviour of the menisci has been described as biphasic, meaning the response of the tissue to applied load is time dependent and determined by both the solid constituents and their interaction with the fluid component [3]. Due to the low permeability of the tissue, deformation results in relative movement of the solid matrix and the fluid it contains, resulting in the creation of drag forces between the two phases. Fluid exudation from the matrix governs the viscoelastic behaviour of the tissue, including stress relaxation and creep [6]. The swelling behaviour of meniscal samples in varying osmotic environments was evaluated in our lab (unpublished data), where they swelled significantly, approximately 30% volumetrically in iso-osmotic phosphate buffered saline (PBS). It was hypothesized that the material properties of the tissue would be affected by this significant swelling. To date, no study has evaluated the effect of sample swelling, due to sample preparation and storage, on the behaviour of the menisci in compression. Therefore, the purpose of this study was to evaluate this relationship. We hypothesized that meniscal samples would be less stiff and more permeable in a swollen state than when they are compressed to the ‘fresh’, non-swollen, thickness prior to initiation of the protocol.