Are porcine flexor digitorum profundus tendons suitable graft substitutes for human hamstring tendons in biomechanical in vitro-studies?

Abstract

Although a plenty of studies exist assessing the strength of ligamentous fixation techniques using porcine flexor digitorum profundus tendons as graft substitutes for human hamstring tendons, there is no biomechanical study comparing these two tendons. To interpret the results obtained with porcine flexor digitorum profundus tendons, knowledge of their biomechanical properties is essential. The purpose of this study was to compare the biomechanical properties of human hamstring tendons and porcine flexor digitorum profundus tendons. A total of six human hamstring tendons and six porcine flexor digitorum profundus tendons were analysed in this study. Quadruple-bundle human hamstring tendons and double-bundle porcine flexor digitorum profundus tendons with a diameter of 9mm were used. Specimens were placed into a tensile loading fixation of a servohydraulic testing machine. Biomechanical analysis included pretensioning of the constructs at 50N for 10min following cyclic loading of 1500 cycles between 50 and 200N at 0.5Hz for measurement of elongation. Subsequently, ultimate failure load and failure mode analysis were performed with a ramp speed of 20mm/min. Human hamstring tendons showed significantly higher maximum load to failure values compared to porcine flexor digitorum profundus tendons (1597±179.6N vs. 1109±101.9N; p=0.035). Human hamstring tendons yielded significantly lower initial elongation during preload, but not during cyclical loading. When porcine flexor digitorum profundus tendons are used as graft substitutes for human hamstring tendons in biomechanical studies, maximum load to failure is underestimated while elongation is comparable to that of human hamstring tendons. Transferring results of biomechanical studies into clinical practice, the lower maximum load to failure of porcine flexor digitorum profundus tendons needs to be taken into consideration.