Tensile properties of an anterior cruciate ligament graft after bone–patellar tendon–bone press-fit fixation

Hardware used for fixation of ACL autografts in bone tunnels frequently complicates revision surgery, requiring two-stage procedures when a bone–patellar tendon–bone (B-PT-B) autograft is used for ACL reconstruction. Therefore alternative procedures that eliminate hardware have been advocated. This study compared the mechanical behavior of two fixation procedures: a widely used interference screw (IFS) fixation and a press-fit fixation that is hardware free. Twenty hind limbs from skeletally mature Saanen breed goats were used in this study, ten each in IFS and press-fit groups. After ACL reconstruction the specimens were dissected, leaving a femur–ACL graft–tibia complex (FATC) for uniaxial tensile testing. The tests included a series of three cyclic creep tests (C1–C3) for the evaluation of residual elongation followed by a tensile load to failure test to obtain linear stiffness and ultimate load of the FATCs. Four of ten specimens failed during the cyclic creep test for the press-fit group, compared to one for the IFS group. For the remaining specimens residual elongation following three cyclic creep tests (C1–C3) was 1.7±0.5 mm in the press-fit group compared to 1.3±0.6 mm in the IFS group, and there was no statistical significant difference between the two fixations. In the load to failure test there was also no statistical significant difference in linear stiffness between the two fixations. However, the ultimate load for the press-fit group (215±75 N) was significantly lower than that for the IFS group (328±103 N). These results provide the basis for future studies involving the time course of healing of these two procedures using the goat model.