Femoral press-fit fixation of the hamstring tendons for anterior cruciate ligament reconstruction

Background: Press-fit fixation of patellar tendon-bone anterior cruciate ligament autografts is an interesting technique because no hardware is necessary. For hamstring tendon grafts, no biomechanical data exist of a press-fit procedure. Hypothesis: Press-fit femoral fixation of hamstring tendons is mechanically equivalent to press-fit patellar tendon-bone fixation. Study Design: Controlled laboratory study. Methods: Patellar and hamstring tendons of 30 human cadavers (age, 53.8 +/- 18.0 years) were used. An outside-in press-fit fixation with a knot in the semitendinosus and gracilis tendons and an inside-out and outside-in fixation with the tendons wrapped around a bone block were compared with patellar tendon-bone press-fit fixation in 30 ovine femora. Constructs were cyclically strained and then loaded until failure. Maximum load to failure, stiffness, and elongation during failure testing and cyclical loading were investigated. Results: The maximum load to failure was 561 +/- 309 N for the patellar tendon, 599 +/- 234 N for the semitendinosus/gracilis tendons knot construct, 678 +/- 231 for the semitendinosus/gracilis tendons bone construct inserted outside in, and 339 +/- 236 for the semitenclinosus/gracilis tendons bone construct inserted inside out (inferior to the others; analysis of variance, Dunn test, P < .01). Stiffness of the constructs averaged 134 +/- 32 N/mm for the patellar tendon, 124 +/- 21 N/mm for the knot construct, 118 +/- 27 N/mm for the outside-in fixation, and 117 +/- 23 N/mm for inside-out fixation. Elongation during initial cyclical loading was 0.7 +/- 0.6 mm for the patellar tendon, 1.6 +/- 0.5 mm for the knot construct, 1.9 +/- 1.2 mm for the outside-in fixation, and 1.9 +/- 0.9 mm for the inside-out fixation (significantly larger for all semitenclinosus/gracilis tendon techniques, P < .05). Conclusions: Failure loads for the semitendinosus/gracilis tendons bone construct inserted outside in and the semitendinosus/ gracilis tendons knot construct were within the confidence interval of the patellar tendon press-fit fixation. All semitenclinosus/gracilis tendon graft techniques exhibited larger elongation during initial cyclical loading than the patellar tendon graft. There was no difference in stiffness between all techniques. Clinical Relevance: Two of the 3 hamstring press-fit fixation techniques showed loads to failure similar to the patellar tendon fixation. Preconditioning of the constructs is critical. These results must be interpreted with care because of high standard deviations.