Twisting and Braiding Reduces the Tensile Strength and Stiffness of Human Hamstring Tendon Grafts Used for Anterior Cruciate Ligament Reconstruction

Background: Twisting and braiding of four-strand hamstring tendon grafts used for anterior cruciate ligament reconstruction has been proposed, but not proven, as a method of improving tensile properties. Hypothesis: Twisting and braiding four-strand human hamstring tendon grafts will have no significant effect on initial graft strength or stiffness. Study Design: Paired in vitro biomechanical study. Methods: In 12 matched cadaveric pairs, a doubled gracilis and semitendinosus tendon graft from one knee was twisted 180° over a 30-mm length, while the doubled tendon graft from the contralateral knee was prepared for biomechanical testing with the graft strands in a parallel orientation. For an additional 12 matched pairs, a doubled graft was braided into a weave while the contralateral graft was prepared for testing in a parallel orientation. All four strands of each doubled tendon graft were equally tensioned with weights before being clamped in a tendon-freezing grip. Tensile testing was then performed. Results: Twisting decreased graft strength by 26% ( P < 0.01) and stiffness by 43% ( P < 0.01), while braiding reduced strength by 46% ( P < 0.01) and stiffness by 54% ( P < 0.01), compared with parallel-oriented grafts. Conclusions: Equally tensioned, parallel four-strand human hamstring tendon grafts were significantly stronger and stiffer than twisted or braided four-strand hamstring tendon grafts. Clinical Relevance: We caution against the use of twisted or braided four-strand hamstring tendon grafts for anterior cruciate ligament reconstruction.