Viscoelastic adaptation of tendon graft material to compression: biomechanical quantification of graft preconditioning
Meyer, Dominik ; Snedeker, Jess ; Weinert-Aplin, Robert ; Farshad, Mazda
In: Archives of Orthopaedic and Trauma Surgery, 2012, vol. 132, no. 9, p. 1315-1320
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- Purpose: The tensile viscoelastic behaviour of tendon tissue is of central biomechanical importance and well examined. However, the viscoelastic tendon adaptation to external compression, such as when a tendon graft is fixated with an interference screw, has not been investigated before. Here, we quantify this adaptive behaviour in order to develop a new method to mechanically precondition tendon grafts and to better understand volumetric changes of tendinous tissue. The hypothesis of this study was that under compressive loads, tendon grafts will undergo a temporary volumetric (and therefore diametric) reduction, due to the extrusion of water from the tendon. Methods: Compressive testing was performed on a material testing machine and load applied through the use of a custom-made mould, with a semi-circular cross section to accommodate the tendon graft. The effects of different compressive forces on the length, diameter and weight of tendon grafts were measured by calipers and a weighing scale, respectively. Further, different strain rates (1 vs. 10mm/min) (n=6, per rate), compression method (steady compression vs. creep) (n=15 for each method) and different compression durations (1, 5, 10min) (n=5 for each duration) were tested to identify the most effective combination to reduce graft size by preserving its macroscopic structure. Results: The effect of compression on volume reduction (75% of initial volume and weight) reached a plateau at 6,000N on an 8-mm tendon bundle. Length thereby increased by approximately 10%. Both steady compression and creeping were able to reduce dimensions of the graft; however, creeping was more effective. There was no difference in effect with different durations for compression (p>0.05) in both methods. Conclusion: The viscoelastic behaviour of hamstring tendon grafts under pressure allows preconditioning of the grafts for reduction of volume and diameter and therefore to drill a smaller bone tunnel, retaining more of the original bone. At the same time, the collagen content of the transplant is preserved and a tight fit of the transplant in the bone tunnel achieved