FREEZING CAUSES ALTERATIONS OF THE COLLAGEN NETWORK IN THE MENISCI: A NEW SCALE TO ASSESS THE ULTRASTRUCTURAL STATUS OF THE MENISCI

Abstract

Introduction and purpose: One of the complications observed after meniscal transplant is allograft shrinkage. Amongst the proposed causes are both a subtle immunological rejection, and an alteration of meniscal permeability leading to nutritional deficit. The purpose of this study was to asses freezing, one of the most frequently used processes to preserve menisci, and provide evidence either in favor of those articles in the literature that claim that freezing does not affect the collagen network, or against it.

Materials and methods: Twenty-six lateral menisci were obtained during total knee replacement. Thirteen were frozen at −80° and the rest were used as a control group. The menisci were analyzed with Transmission Electronic Microscopy. According to the periodicity and degree of disruption of the collagen, loss of band pattern and intrafibrillar edema, each meniscus was scored from 0 to 7 points. Subsequently the menisci were classified by degrees from normal (grade I, 0 to 2 points) to severely altered (grade III, 5 to 7 points).

Results: Collagen fibers in longitudinal sections averaged 14.26 nm in previously frozen menisci and 17.28 in the control group (p=0.019), whereas in cross sections they averaged 13.14 nm. vs. 16.93 nm. respectively (p=0.003)..

Eight of the 13 frozen menisci were classified as grade III (61.54%) and 5 as grade II. In the control group 6 were classified as grade I (46.15%) and 7 as grade II (53.85%). Frozen menisci averaged 4.85 points and the control menisci 2.46 (p< 0.001).

Conclusions: The freezing process to −80°C seems to alter both each fiber of collagen as well as its spatial position. We have presented a new qualitative/quantitative assessment scale for meniscal status.