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The Effect of Donor Age and Low-Dose Gamma Irradiation on the Initial Biomechanical Properties of Human Tibialis Tendon Allografts

Laura L. Greaves^,*, Aaron T. Hecker, MS and Charles H. Brown, Jr, MD^,||

From the Division of Orthopaedic Engineering Research, Department of Mechanical Engineering, University of British Columbia and Vancouver General Hospital, Vancouver, British Columbia, Smith & Nephew Endoscopy, Research and Development, Mansfield, Massachusetts, Department of Orthopaedic Surgery, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, and ^|| Abu Dhabi Knee and Sports Medicine Center, Abu Dhabi, United Arab Emirates

^* Address correspondence to Laura L. Greaves, Division of Orthopaedic Engineering Research, Department of Mechanical Engineering, University of British Columbia and Vancouver General Hospital, 828 West 10th Ave, Room 500, Vancouver, BC V5Z 1L8, Canada (e-mail: lauragreaves{at}gmail.com).

Background: Most tissue banks recover and irradiate tibialis tendon allografts from donors aged up to 65 years. It is unknown whether donor age and low-dose gamma irradiation affect the initial biomechanical properties of tibialis allografts.

Hypothesis: Donor age up to 65 years and low-dose gamma irradiation do not significantly affect the initial biomechanical properties of tibialis allografts.

Study Design: Controlled laboratory study.

Methods: One hundred twenty-six tibialis tendon allografts (63 pairs, 37 human donors) were divided into 3 age groups: young (<45 years), middle (46–55 years), and old (56–65 years). Within each age group, half of the paired tendons underwent tensile testing as single-strand grafts and the other half as double-strand grafts. One tendon from each donor pair was randomly assigned to undergo terminal sterilization with an absorbed dose of 1.46 to 1.80 Mrad (14.6–18.0 kGy) gamma irradiation, whereas the other tendon received no irradiation. All tendon grafts were preconditioned with a cyclic load and tested to failure in tension.

Results: Irradiated single-strand tendons in the old age group had a longer displacement at failure compared to the middle but not the young age group. Nonirradiated double-strand tendons in the old age group had a lower failure stress. Single-strand irradiated old tendons had a lower stiffness, and all irradiated young tendons and old double-strand tendons had a higher failure stress compared to nonirradiated tendons.

Conclusion: Donor age up to 65 years does not significantly affect the initial failure load, stiffness, or displacement at failure of tibialis allografts. An age-related decrease in failure stress was observed among nonirradiated tendons but not in tendons subjected to irradiation.

Clinical Relevance: The results provide biomechanical evidence for use of tibialis allografts from donors up to 65 years of age. Low-dose gamma irradiation does not negatively influence the initial biomechanical properties of tibialis allografts. Further studies examining age and irradiation effects after submaximal cyclic loading conditions are recommended.

Key Words: allograft • anterior cruciate ligament (ACL) • gamma irradiation • tibialis tendons