Effect of cyclic tension on the biomechanical properties of flexor tendon grafts. Results of an ex-vivo porcine study

Background: Autologous flexor tendons are widely used for anterior cruciate ligament (ACL) reconstruction. Pretension of the graft before fixation has been described as part of the surgical technique, nevertheless there is no consensus on the type and amount to tension needed to increase the stiffness without affecting its biomechanical properties. Our hypothesis is cyclic tension increases flexor tendon stiffness without affecting its ultimate failure at maximum loads (UFML). Methods: Forty-five flexor digitorum profundus tendons harvested from domestic pigs (Sus scrofa domestica) were randomly divided into three groups: El (n = 15), E2 (n = 15) and C (n = 15). Groups El and E2 were subjected to 50 cyclic loads at a 1 Hz frequency, at 70 N and 100 N respectively, group C was not intervened. The three groups were then tested for UFML. Cyclic loads and measurements were performed using a Stress-Strain machine (SST 1.0 Kinetecnic (R)). Results were analyzed using GrapgPad statistical software. Groups were compared using Mann-Whitney test with a 95% confidence interval. Results: Significant increased stiffness for group El (p = 0.02) and group E2 (p < 0.01) when compared to group C. The stiffness of group E2 was also significantly higher than El (p = 0.03). There was a significant reduction on the UFML between group E2 and C (p < 0.01), which was not observed when comparing groups El and C. Conclusion: Cyclic loads at 70 N result in an increased stiffness of flexor tendons without affecting its ultimate failure at maximum loads. Cyclic loads at higher tensions might cause a deleterious effect on the biomechanical properties of flexor tendon grafts. (C) 2014 Elsevier B.V. All rights reserved.