THE EFFECTS OF FREEZE-DRYING AND ETHYLENE-OXIDE STERILIZATION ON THE MECHANICAL-PROPERTIES OF HUMAN PATELLAR TENDON

Human patellar tendon allografts are used to replace injured anterior cruciate ligaments. They are often stored by freeze-drying or freezing before use and have been sterilized by gamma irradiation or ethylene oxide gas. Studies comparing the mechanical properties of tendons pres erved by freeze-drying and sterilized by ethylene oxide have yielded c onflicting results. This study examined the effects of freeze-drying a nd ethylene oxide sterilization on the mechanical properties of human patellar tendons obtained from 11 human cadavers; all were free of mus culoskeletal disease. The 22 patellar tendons were halved longitudinal ly; 7 were frozen at -70-degrees-C for 8 weeks and served as controls; 8 were freeze-dried; and 7 were freeze-dried and sterilized with ethy lene oxide gas. Ultimate tensile stress and longitudinal strain were g reater for frozen than for freeze-dried, but not greater than freeze-d ried, ethylene oxide-sterilized tendons (P < 0.05). The modulus of ela sticity was similar in all tendon groups. The study suggests that some in vitro mechanical properties of frozen tendons may be marginally su perior to the properties of freeze-dried tendons, even after correctio n for size difference. Ethylene oxide gas sterilization had no adverse effect on tendon mechanical properties.