Methodology and apparatus to determine material properties of the knee joint meniscus

This paper describes a soft tissue test method and apparatus which determines the constants necessary to characterise the elastic properties of a transversely isotropic material such as the knee joint meniscus. The tensile machine was designed to test small delicate samples in a humidified environment and measure specimen deformation with a CCD video camera. The method described here employs a common specimen preparation procedure and test protocol using specimens with four different fibre orientations. Discrete markers (0.075 mm graphite particles) permit repeatable measurements of two-dimensional strain on the specimen surface enabling the determination of Poisson's ratio characteristics. Shear strain was also measured in tensile test specimens prepared with an oblique collagen fibre orientation, offering an alternative method to investigate shear properties. Regional strain measurements provide an assessment of the uniformity of the tissue deformation. Preliminary results on bovine menisci are presented as an application of the test system. Material properties characterising the meniscus tissue were obtained with one test procedure and identical coupon size. This has the advantage of avoiding systematic errors caused by different preparation techniques, test procedures and equipment.