Abstract
Most cases of tendinopathy are believed to be overuse injuries rather than the result of a chronic event. The investigation of the fatigue properties of tendon is therefore of critical importance. This work considered the cyclic stress-relaxation and creep behaviour of two contrasting bovine tendon types – the largely postional digital extensor and the more energy storing deep digital flexor tendon. Fascicles were cyclically loaded (1Hz), to 1800 cycles of stress relaxation or to failure in creep, stopping some tests at 300, 900 or 1200 cycles to perform quasi-static failure tests or confocal imaging using a highly concentrated Acridine Orange solution. Creep tests were cycled to 60% of the ultimate tensile strength (UTS), while for stress relaxation, cyclic deformation to the strain associated with 60% UTS was used. Flexor tendon fascicles were found to exhibit reduced stress relaxation at all time points compared to the extensor fascicles and also showed an increase in the mean cycles to failure during creep testing. Evidence of fatigue damage was clear in the confocal images with breakdown of the collagen fibre alignment evident from 300 cycles; however it appears that some damage could occur without effect on the UTS of the fascicle. Despite what appears to be superior fatigue resistance in the flexor tendon fascicles, the matrix damage, certainly at early time points, appeared visually to be as severe as that observed with the extensor tendon fascicles.
