Biomechanical comparison of Cross-pin and Endobutton-CL femoral fixation of a flexor tendon graft for anterior cruciate ligament reconstruction--a porcine femur-graft-tibia complex study.

BACKGROUND: A stable fixation of the graft is imperative for early aggressive rehabilitation after anterior cruciate ligament (ACL) reconstruction. The suspension devices such as Endobutton-CL and Cross-pin system are common techniques of femoral fixation for the hamstring tendon graft and provide superior initial biomechanical properties than the screws system. It remains unclear how such implants perform under cyclic loading and initial pull-out strength.

MATERIALS AND METHODS: Cross-pin and Endobutton-CL femoral fixation devices were tested for initial fixation strength in porcine knee joints by cyclic loads following a load-to-failure test. The Cross-pin and Endobutton-CL were used for femoral fixation of a porcine profundus flexor digitorum tendon autograft in 20 porcine knees. Ten specimens of femoral-graft-tibia complex in each group were loaded cyclically to between 0 and 150 N at 1 Hz for 1000 cycles following a load-to-failure test at a rate of 150 mm/min.

RESULTS: The amount of total femur-graft-tibia complex graft displacement was significantly lower in the Cross-pin fixation group (5.37 +/- 0.28 mm) than in Endobutton-CL fixation group (6.08 +/- 0.61 mm: P < 0.05). There were no significant differences in the maximal failure load, yield load, and stiffness between the Cross-pin and Endobutton-CL fixation groups.

CONCLUSIONS: This biomechanical study reveals that the Endobutton-CL and Cross-pin femoral fixation devices have an equally strong and safe fixation for ACL reconstruction. However, the Cross-pin fixation has significantly less displacement of femur-graft-tibia complex than that of Endobutton-CL fixation in response to the cyclic loading test. It indicates that the Cross-pin fixation is more suitable for early aggressive rehabilitation following ACL reconstruction.