Tibial press-fit fixation of the hamstring tendons for ACL-reconstruction

Press-fit fixation of patellar tendon bone anterior cruciate ligament autografts is an interesting technique because no hardware is necessary to achieve fixation. Up till the present point, there is no biomechanical data available for the tibial press-fit fixation of the hamstring tendons. Hamstring tendons of 21 human cadavers (age: 41.9 +/- 13.1 years) were used. A press-fit fixation with looped semitendinosus and gracilis tendons secured by a tape (T) over a bone bridge, or by a baseball-stitched suture (S), was compared with degradable interference screw fixation (I) in 21 porcine tibiae. The constructs were cyclically strained and subsequently loaded to failure. The maximum load to failure, stiffness, and elongation during cyclical loading were measured. The maximum load to failure was highest for the T-fixation at 970 +/- 83 N, followed by the I-fixation with 544 +/- 109 N, and the S-fixation with 402 +/- 78 N (P < 0.03). Stiffness of the constructs averaged 78 +/- 13 N/mm for T, 108 +/- 18 N/mm for S, and 162 +/- 27 N/mm for I (P < 0.03). Elongation during initial cyclical loading was 2.0 +/- 0.6 mm for T, 3.3 +/- 1.1 mm for S, and 1.4 +/- 0.5 mm for I (S inferior to I and T, P<0.05). Elongation between the 20th and 1,500th loading cycle was lower for T (2.2 +/- 0.7 mm) compared with I (4.1 +/- 2.7 mm) and S (4.8 +/- 0.7 mm; P < 0.001). The T-fixation technique exhibited a significantly higher failure load than the S-, and I- techniques. All techniques exhibited larger elongation during initial cyclical loading than is reported in the literature for grafts with bone blocks. Only one technique (T) showed satisfactory elongation behavior during long-term cyclic loading. Interference screw fixation demonstrated significantly higher stiffness. Only one of the investigated techniques (T) seemed to exhibit adequate mechanical properties necessary for early aggressive rehabilitation programs.