Mechanical assessment of two different methods of tripling hamstring tendons when using suspensory fixation.

PURPOSE

To investigate two different methods of suture fixation and tendon behaviour when using an Endobutton and a tripled tendon.

METHODS

Thirty bovine tendons and foam blocks were randomly allocated to three groups: group 1: The tendon was doubled through 40-mm Endobutton; group 2: Tripled tendon--whip-stitched with No. 2 Ultrabraid, passed through an Endobutton and third limb secured to the loop via seven knots; and group 3: Tripled tendon--whip-stitched with No. 2 Fibreloop and fixed as group 2. A tunnel matching the graft diameter was drilled through the block. The graft was passed through the tunnel and fixed with an interference screw. The constructs were cycled at 1 Hz from 10 to 50 N for 10 cycles followed by 50-250 N at 1 Hz for 500 cycles. Load-to-failure test was then carried out at a rate of 20 mm/min. A custom digital image capture technique was used to measure and calculate displacement, strain and stress. Statistical analysis was carried out using Kruskal-Wallis test and paired t test.

RESULTS

There was no statistical significant difference between ultimate tensile strength (UTS) (P = 0.35) and yield load (0.41) between the 3 groups. The mean displacement of the third tendon limb in group 2 was 4.8 mm and in group 3, 1.5 mm. Displacement was not statistically significant (P = 0.07). The mean stress in the third limb versus the doubled portion of tendon in group 2 was 0.4 ± 0.02 versus 4.8 ± 0.52 MPa and in group 3, 0.5 ± 0.03 versus 5.2 ± 0.52 MPa.

CONCLUSIONS

In this biomechanical study, there was no mechanical difference in the overall properties between a doubled and tripled tendon graft. Significant cyclic elongation occurred in the third limb of the tripled tendon in comparison with the doubled portioned. Further work is needed to determine whether these mechanical findings translate to clinical practice. Caution should be used when tripling hamstring grafts. In particular, tripling small grafts provides no biomechanical advantage immediately and possibly long term, thus potentially increasing the risk of failure.