Viscoelastic adaptation of tendon graft material to compression: biomechanical quantification of graft preconditioning.
OBJECTIVE
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. 10 mm/min) (n = 6, per rate), compression method (steady compression vs. creep) (n = 15 for each method) and different compression durations (1, 5, 10 min) (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 6,000 N 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.


CONCLUSIONS
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.
Department of Orthopedics, University of Zürich, Balgrist, Forchstrasse 340, 8008, Zürich, Switzerland.
Dominik C
DC
Meyer
Jess G
JG
Snedeker
Robert A
RA
Weinert-Aplin
Mazda
M
Farshad
D000222:Adaptation, Physiological; D000818:Animals; D001696:Biomechanical Phenomena; D002417:Cattle; D019245:Compressive Strength; D004548:Elasticity; D008422:Materials Testing; D023421:Models, Animal; D011312:Pressure; D012756:Sheep; D013710:Tendons / Q000502:physiology* / Q000637:transplantation; D013718:Tensile Strength; D019737:Transplants; D014783:Viscosity