The effect of sterilization and storage on the viscoelastic properties of human tendon allografts

Allografts have become increasingly preferred for anterior cruciate ligament replacement purposes. The risk of infections necessitates thorough sterilization procedures, and the allografts usually need to be stored prior to surgery. Classical mechanical tests have been performed with various types of tendons, however, tibialis anterior and peroneus longus tend to suffer the least biomechanical changes after irradiation. Only few results are available of the strain and creep behaviour of tendons, even though this information is necessary to provide suitable allografts. The aim of the present study is to analyze the effect of different tendon types (T-tibialis anterior, P-peroneus longus), sterilization methods (G-gamma irradiation of 21 kGy, E-electron beam irradiation of 21 kGy) and storage times (5 and 6 months) on the creep behavior, which is characterized by the strain at the end of the loading phase and creep deformation after static loading. Static creep tests were performed with 250 N load during 60 s. Deformation at the end of the loading phase of both tendons was significantly smaller after 5 months long storage than that after 6 months long storage. TE5 showed significantly less creep than group TE6, and TE6 significantly greater than PE6. The creep of TE5 was significantly lower than that of TG5. Based on the data, the peroneus longus sterilized by electron beam and stored deep frozen for 5 months is a better choice for anterior cruciate ligament reconstruction than tibialis anterior sterilized by gamma irradiation stored for 6 months.