[In vitro study of the role of various preservation methods on mechanical properties of allografts of the patellar tendon].

Tendon allografts are presently used for surgical reconstruction of the anterior cruciate ligament. The aim of this study was the in vitro evaluation of the modification of the mechanical properties of conserved human patellar tendons, deep-frozen or freeze-dried and sterilized with gamma rays. Thirty pairs of patellar tendons (central third) with their bony attachments were removed from fresh corpses, frozen in liquid nitrogen, then conserved at -80 degrees C. Out of each pair, one tendon was submitted to an additional treatment and the other was used as a control. Three types of treatment were studied: 2.5 Mrad irradiation (groupe I), freeze-drying with 1% residual humidity (groupe II), consecutive freeze-drying and irradiation (group III). After warming up (controls and group I treated tendons), the specimens were submitted to mechanical tests on the pulling machine with a suitable arrangement. Two types of tests were performed: a creep test (80 cycles at 1 Hz between 0 and 50 N) then an ultimate tensile strength test (0.25 mm/s). Freeze-drying causes macroscopic morphological alterations, which are even more marked if irradiation is applied in addition. The three types of treatment induce an increase in creep and a decrease in the ultimate, tensile strength and in Young's module, all being statistically significant. The three types of treatment alter the mechanical properties of the allograft. Freeze-drying maintains a better resistance of the graft. The combination of freeze-drying and irradiation is the most damaging method, and freeze-drying even seems to potentialize the harmful effects of irradiation resistance (group II freeze-dried grafts), the treated allografts present with changes in their viscoelastic properties that are incompatible with their clinical use. This study has also shown that some parameters influence the extent of the damaging effects of these three treatments, and experiments are being continued to optimize the conservation and sterilization procedure.