| Objective:With rapid development of the international competitive sports and apparent increase of traffic accidents, the incidence of knee cruciate ligament injury has significantly increased. So the operation of cruciate ligament reconstruction is becoming a major method l to treat ligament injury. Graft There are varieties kind of graft, including autologous ligament, allograft ligament and artificial ligament. Comparing with autologous, allograft ligament reconstruction can gain similar clinical effect, especially for multi-ligament rupture and further renovation. However, allograft ligament should be given special treatment before transplant in order to reduce the immune response and the chance of disease spreading. Allograft ligament often sources from patellar ligament, semitendinosus tendon, gracilis tendon, quadriceps tendon and so on. These tendon grafts need to cryopreserved to reduce antigenicity and retain the biological activity before operation. However, there was no reports regarding on the thermal stability of tendon after cryopreservation, so our study aimed at evaluating the thermal stability of human hamstring tendons which were put in -80°C fridge and -196°C liquid nitrogen and we calculated the degeneration temperature and degeneration enthalpy by differential scanning calorimetry techniques by which we can evaluate the thermal stability of hamstring tendon.Methods:Our study chose 23 patients who were treated by the NO. Three Hospital of Hebei Medical University from September 2008 to December 2008 and was diagnosed as anterior cruciate ligament injury(ACL) by MRI and arthroscopy and needed to accept ACL reconstruction.Informed consent by patients, we began to take away hamstring tendons in the anterior cruciate ligament reconstruction surgery after finding the anterior cruciate ligament injured by arthroscopy. On the condition of no influence on the use of surgical graft cases, we chose three 3mm×3mm×1mm tendon blocks from each semitendinosus tendon and gracilis tendon. Each tendon was randomly divided into three groups, namely, Fresh group, Frozen group and Nitrogen group. Semitendinosus tendon blocks and gracilis tendon blocks in Fresh group were sent to the laboratory immediately, the other two groups were preserved separately at -80°C fridge, -196°C liquid nitrogen for four weeks and then sent to the laboratory. We used differential scanning calorimeter (DSC) measuring the peak temperature (Tm), peak heat (Qm), calculate the change of collagen denaturation enthalpy (ΔHm) and the amout o of the three helix structure f collagen fibers (%) in each group. By comparing degeneration enthalpy and quantitative analysis of three helix structure of tendons in each semitendinosus muscle and gracilis muscle group, We evaluated the thermal stability of human hamstring tendons by different methods of preservation.Results:1,Comparisons between each semitendinosus tendon and gracilis tendon group: there is no significantly differences(P> 0.05) between semitendinosus tendon and gracilis tendon at the quality of the sample (mg), the initial temperature (°C), the initial heat (mv), terminal temperature (°C), terminal heat (mv), peak temperature (°C), peak heat (mv), denaturation enthalpy change (J / g) and the amount of three helix structure (%)in fresh group, frozen group and nitrogen group.2,Comparisons among fresh group, frozen group and nitrogen group: Among the three groups, semitendinosus tendon has no significant differences (P> 0.05) at the quality of sample (mg), the initial temperature (°C), the initial heat (mv), the terminal temperature (°C), terminal heat (mv). Gracilis tendon also has no significant differences (P> 0.05) at the quality of the sample (mg), the initial temperature (°C), the initial heat (mv), the terminal temperature (°C), terminal heat (mv) among the three groups. Compared with fresh group, there is a decline in peak temperature (°C), peak heat (mv), denaturation enthalpy change (J / g) and the amount of three helix structure (%) of semitendinosus tendon in frozen group and nitrogen group.There is a significantly decline in frozen group than in nitrogen group and the three groups has a significant difference (P <0.05). Gracilis tendon in frozen group and nitrogen group declined in peak temperature (°C), peak heat (mv), denaturation enthalpy (J / g) and the amount of three helix structure (%)compared to fresh group, and the three groups have a significant difference (P <0.05).Conclusion1.There are different degrees of declines about the thermal stability of collagen molecules of humans hamstring tendons after different methods of low-temperature preservation.2. The thermal stability of humans hamstring tendons of -80°C frozen preservation is better than that of -196°C liquid nitrogen preservation.3. There is no difference about the thermal stability of collagen molecules between semitendinosus tendon and gracilis tendon at the same cryopreservation method.
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