INTRODUCTION: Shrinkage is one of the complications observed after allograft meniscal transplantation. Subtle immune rejection and alterations in meniscal permeability leading to nutritional deficit have been suggested as causes of shrinkage. The purpose of this study was to ascertain how freezing, one of the most common procedures used to preserve allografts, alters the collagen’s architecture.

METHODS: 26 fresh human external menisci were harvested in sterile conditions during TKR procedures. 13 of them were immediately frozen to −80° C while the rest were used as controls. All the menisci were cut, processed and preserved in a 2.0% glutaraldehyde and then analyzed with transmission electron microscopy. Four hundred collagen fibrils were recorded and measured in longitudinal and transversal sections in each meniscus. According to the collagen’s periodicity and degree of disruption, loss of banding, degree of collagen packing, fibril size variability and its intrafibrilar oedema, each meniscus was pointed from 0 to 7. Subsequently they were classified in grades ranging from a normal state (grade I; 0 to 2 points) to severe disarray (grade III; 5 to 7 points).

RESULTS: The fibril collagen diameters of those menisci that had been previously frozen showed an average size in the longitudinal section of 14.256 nm, whereas 17.279 nm were seen in the menisci used as controls (p=0.019). In the transverse section, the frozen menisci averaged 13.145 nm and 16.935 nm the controls (p=0.003).

Samples of the 13 previously frozen menisci were classified as grade III in 8 cases (61,54 %), and grade II in 5 cases (38.46 %). They averaged 4.846 points. The control groups were classified as grade I in 6 cases (46.154%) and grade II in 7 cases (53.85 %). The frozen menisci averaged 4.85 points whereas the control group did so 2.46 (p< 0.001)

CONCLUSIONS: The fibril diameters in frozen menisci showed a thinner diameter and had a higher degree of disarray. Therefore, the results suggest that the freezing process alters the menisci’s collagen net. This could partially explain the pathological changes found in shrunken menisci. This is the first work that quantified and qualified methodologically the collagen meniscal architecture and its potential changes.