[Allografts for cruciate ligament reconstruction]

Cryopreservation with glycerol improves the in vitro biomechanical characteristics of human patellar tendon allografts

PURPOSE

To evaluate the in vitro biomechanical characteristics of patellar tendon ligaments (BTB) when stored as fresh frozen or as glycerol cryopreserved allografts.

METHODS

Seventy patellar tendons were harvested from 35 cadaveric human donors and randomly assigned into seven groups. Grafts in group FRESH were mechanically tested within 2 h of harvesting. FROZ-3, FROZ-6, and FROZ-9 were deep-frozen to -80 °C for 3, 6, and 9 months, respectively. Grafts in groups CRYO-3, CRYO-6, and CRYO-9 were initially incubated with 10% glycerol in a phosphate-buffered saline for 1 h and then stored in glycerol solution (10% glycerol in PBS) at -80 °C for 3, 6, and 9 months, respectively. Grafts were mechanically tested with two cycling modes (50-250 °N and 150-500 °N) and then loaded to failure.

RESULTS

Cryopreserved grafts demonstrated more consistent results and expressed lower elongation rates after both cycling loading protocols compared to their frozen counterparts at all storage times. During load-to-failure analysis, ultimate stiffness levels were predominantly higher (23.9-61.5%) in cryopreserved grafts compared with frozen grafts, and ultimate stress levels were 26% (13.3-47.7%) higher, regardless of the storage time. Moreover, cryopreserved grafts revealed similar ultimate elongation and uniformly higher ultimate stiffness and ultimate stress levels compared to fresh grafts.

CONCLUSION

The results of this in vitro study demonstrated superior mechanical properties of cryopreserved grafts compared to frozen grafts within a preservation period of 9 months. Cryopreservation with glycerol solution might be used to further improve the quality of preserved soft-tissue allografts.