Anterior cruciate ligament reconstructions are commonly performed using hamstring tendon autografts. Some surgeons believe that twisting the graft increases its strength under load. Tensile testing of grafts concluded that twisted grafts are weaker and less stiff than parallel grafts. These tests do not consider the varied tendon loads that occur during flexion and extension and thus may not accurately predict graft strength.

In this research, a model is developed of twisted and parallel hamstring grafts during flexion and extension under applied tibial displacements. A four-bar linkage is used to define the relative position of the femur with respect to the tibia and line elements were used to model the tendon strands. The grafts are also modelled under tensile loading conditions using line and helical elements to examine the validity of the model.

The physiological loading of the graft models shows that the twisted graft has greater laxity than the parallel graft, although it shows little difference in failure load for the two configurations. The tensile loading of the graft models shows little difference in failure load when the tendons are modelled using line segments. When the tendons are considered as three dimensional helical elements, which more accurately describes the tendon structure, the failure load of the twisted graft decreased significantly. This research provided no evidence to support the belief that a twisted tendon graft is a superior graft configuration relative to a parallel tendon graft.