Effects of preservation on the tensile properties and structure of the meniscus

Meniscus allografts must be transplanted shortly after harvest or be preserved until transplantation, typically by freezing. However, the effects of preservation on the structure-function relationship of the meniscus are not well understood. The objective of this study was to propose a physical mechanism by which preservation affects the tensile properties of the meniscus. It is hypothesized that the separation of collagen fibres from voids formed during freezing and fresh storage decrease tensile strength and modulus. Medial and lateral porcine menisci were dissected on the day of slaughter and allocated into four groups: processed immediately (controls), fresh storage (4 °C, 21 days), or frozen with (-140 °C, 21 days) and without cryoprotectant (-80 °C, 21 days). Tensile tests were performed in the circumferential and radial directions to measure tensile modulus, ultimate tensile strength (UTS), and ultimate strain in the circumferential and radial directions. Area void fractions of collagen fibre bundles were estimated from scanning electron microscopy images. All preservation groups had a significantly lower modulus, UTS and a significantly greater void fraction than controls. Menisci frozen with cryoprotectant had a significantly greater modulus, UTS and a significantly lower void fraction than those frozen without. No significant differences in mechanical or structural properties were found between the freezing without cryoprotectant and fresh storage groups. Decreases in tensile properties may result from interfibrillar changes such as fibril spacing and crosslinking. Future tensile studies should include dynamic mechanical analysis, physiological strain rates, and a physically representative material model.