Alterations in meniscal permeability leading to nutritional deficit have been suggested as a cause of shrinkage in meniscal transplantation. The purpose of this study was to ascertain how freezing, one of the most common procedures used to preserve meniscal allografts, alters the collagen's architecture. Twenty-six fresh human external menisci were analyzed with transmission electron microscopy. Thirteen of them were previously frozen at -80 degrees C while the rest were used as controls. A new scale of the collagen meniscal architecture was proposed 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 scored from 0 to 7. Subsequently they were classified in grades ranging from a normal state (grade I; 0-2 points) to severe disarray (grade III; 5-7 points). The fibril collagen diameters of those menisci which had been previously frozen showed an average size in the longitudinal section of 14.26 nm, whereas it was 17.28 nm in the menisci used as controls (p=0.019). In the transverse section, the frozen menisci averaged 13.14 and 16.93 nm in the controls (p=0.003). Samples of the 13 previously frozen menisci were classified as grade III in 61.54% of the cases. In the control group, all the menisci were classified either as grade I or II. The frozen menisci averaged 4.85 points, whereas the control group did so at 2.46 (p<0.001). 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 after transplantation.

Fresh frozen menisci have recently been shown to have an altered meniscal ultrastructure. The cause might be a deterioration of its permeability due to collagen net disarray. The purpose of this study was to evaluate the cryopreserved meniscus in terms of ultrastructure and cellularity. Ten fresh human lateral menisci were harvested. Collagen architecture was evaluated with transmission electron microscopy. The Collagen Meniscal Architecture scoring system was used to assess the degree of meniscal disarray. Cell population, was also evaluated. The fibril collagen diameters of those menisci which had been previously cryopreserved showed an average size in the longitudinal section of 12.6 +/- 1.3 nm, whereas it was 13.4 +/- 2.2 nm in the menisci used as controls (n.s.). In the transverse section, the cryopreserved menisci averaged 15.5 +/- 2.4 and 16.7 +/- 3.5 nm in the controls (n.s.). The study group scored 4.8 points +/- 1.7, whereas the control group did so at 4.1 +/- 1.3 (n.s.). The percentage of cell survival after the cryopreservation ranged from 4 to 54. The fibril diameters and degree of disarray showed a similar distribution in both groups. The results suggest that meniscal cryopreservation does not alter the meniscal ultrastructure. Therefore, an allograft stored in that way would not alter its biomechanical properties, although its cellular viability is highly unpredictable.

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Only a few cases of the nearly unknown hypoplastic meniscus abnormality have been described. A case report of an incidental finding in a young female with a bilateral hypoplastic medial menisci is presented and, as far as we know, is the first report of bilateral hypoplasia of the medial meniscus in the literature.