The effect of deep-freezing on the structure of patellar and Achilles tendon allografts used for ACL reconstruction

According to the literature and to our recent studies, utilization of different types of allografts is a useful method for the reconstruction of the injured anterior crucial ligament. Of the different kind of allografts, in our practice, the patellar and Achilles tendons are the most commonly used types. Following our protocol, these allografts are subjected to cryopreservation at ?80 °C until utilization. The purpose of this study was to analyse the effects of cryopreservation at ?80 °C on the histological and structural properties of the human patellar and Achilles tendons. Total of four patellar and five Achilles tendons with human origin were collected for this study. The samples were subjected to fresh freezing and cryopreservation at ?80 °C. After 1, 3, 6, 12 and 24 weeks, the structure of the frozen tendons was compared to freshly collected samples by standard histological examination and thermal analyses, using differential scanning calorimetry (DSC). The thermal denaturation of different parts of human samples was monitored by a SETARAM Micro DSC-II calorimeter. The data treatment after ASCII conversion was done by Origin 6.0. DSC scans clearly demonstrated significant differences between the fresh and frozen samples. The decrease in collagen fibril density was supported by calorimetric and histological analyses in a time-dependent fashion. Our data suggest that application of allografts requires special attention paid to the proper storage time. The selection of grafts with possibly shorter storage time is recommended.