Effects of Preservation on the Compressive Properties and Microstructure of the Knee Meniscus

Meniscus transplantations commonly use tissue preserved by freezing or fresh storage. However, the mechanisms by which preservation affects mechanical properties are not well understood. The objective of the present study was to determine whether structural and mechanical properties of menisci differ after being preserved by freezing or prolonged fresh storage. Preservation is hypothesized to negatively affect the elastic and viscoelastic compressive properties of the meniscus through structural void formation.

Medial and lateral porcine menisci were obtained on the day of slaughter and allocated into four groups: processed immediately after dissection (controls), preserved in culture medium (4 °C, 21 days), or frozen with (- 140 °C, 21 days) and without cryoprotectant (- 80 °C, 21 days). Permeability, compressive moduli, peak stress, and tangent moduli were determined from multi-ramp stress relaxation tests (confined compression). Femoral and tibial surfaces were imaged with scanning electron microscopy and used to estimate the area porosity. Comparisons were made using ANOVA with linear contrasts.

Compared with controls, freezing and fresh storage led to increased permeability and decreased aggregate modulus, peak stress, and tangent modulus along with increased porosities estimated from electron micrographs (p < 0.028). Menisci frozen with cryoprotectant showed intermediate mechanical and structural properties between the control and frozen groups.

Freezing and fresh storage negatively affected the mechanical properties of porcine meniscus, with a possible mechanism being the creation of microstructural voids. Reducing ice formation during freezing with alternative cold preservation techniques may help retain physical properties, leading to improved guidelines for meniscal storage.