[The development and biomechanical testing of a femoral press fit fixation for hamstring tendons]

Abstract

Purpose: The purpose of this study was to investigate press fit femoral fixation of hamstring tendons and to compare the mechanical properties with press fit patellar tendon bone (PTB) fixation.

Methods: The PTB and hamstring tendons of 30 human cadavers (age: 55.8+/-18.0 years) were used as grafts. An outside-in press fit fixation with a knot in the semitendinosus and gracilis graft (SG-K) and an inside-out (SG-BI) and an outside-in fixation (SG-BO) with the tendons looped over a bone block were compared with a bone-patellar tendon (PT) press fit fixation in 30 bovine femora. The angle between the direction of force and bone tunnel was 60 degrees. The constructs underwent 20 cycles of loading between 60 and 260 N. Constructs were loaded until failure at a speed of 1 mm/sec. Graft fixation was analyzed in terms of maximum load to failure, stiffness and elongation during cyclic stretching. A video analysis of length changes was investigated.

Results: There was a significant difference in the maximum load to failure. The SG-BI fixation was inferior to the other three techniques (Mann-WhitneyU-test, P<0.01). There was no difference in stiffness between the techniques. Length changes of PT-fixation from the first to the fifth loading cycle were significantly smaller compared with all other groups (0.73+/-0.58 mm). There was no significant difference between the groups from the 15th to the 20th cycle of cyclic loading.

Conclusions: Press fit fixation of hamstring grafts is technically challenging. However, pull-out forces for SG-O and SG-K were equivalent to BPT-graft fixation. Adequate preconditioning for all hamstring tendon press fit techniques is crucial.