Age-related changes in mechanical properties of semitendinosus tendon used for anterior cruciate ligament reconstruction

Background Hamstring tendons are a popular choice for autografts in anterior cruciate ligament (ACL) reconstruction. However, there is increasing evidence that hamstring tendon autografts carry a high risk of revision and residual instability in young patients. To elucidate the reasons for the inferior outcome of the reconstructed ACL with hamstring tendon autografts in young patients, we investigated the Young's modulus and the extent of cyclic loading-induced slackening of the semitendinosus tendon used for ACL reconstruction across a broad range of ages. Methods Twenty-six male patients (aged 17-53 years), who were scheduled for ACL reconstruction surgery using the semitendinosus tendon autograft, participated in this study. The distal portion of the harvested semitendinosus tendon, which was not used to construct the autograft, was used for cyclic tensile testing to calculate the Young's modulus and the extent of slackening (i.e., increase in slack length). Results Spearman correlation analysis revealed that the Young's modulus of the semitendinosus tendon was positively correlated with the patient's age (rho = 0.559, P = 0.003). In contrast, the extent of tendon slackening did not correlate with the patient's age. Conclusions We demonstrated that the Young's modulus of the semitendinosus tendon increases with age, indicating that the semitendinosus tendon used for ACL reconstruction is compliant in young patients.