Anterior cruciate ligament reconstruction with short hamstring grafts: the choice of femoral fixation device matters in controlling overall lengthening.

PURPOSE

The purpose was to conduct an independent biomechanical study comparing the main types of femoral fixation adapted to short hamstring grafts in anterior cruciate ligament (ACL) reconstruction surgery and to validate their performance.

METHODS

The ACLip Femoral, ToggleLoc™ Ziploop (TLZ), and Tape Locking Screw (TLS) implants were tested in tension in the following three different configurations: implant alone, implant fixed on the femur without graft, and implant fixed on the femur with graft. Grafts alone were also tested. The femurs and the 4-strand semi-tendinosus grafts were derived from porcine and human models, respectively. Each set-up was subjected to the same protocol of creep (50 N for 30 s), cycling (1000 cycles between 50 and 250 N, 1 Hz), and load to failure (50 mm/min).

RESULTS

A total of 93 tests were performed (30 ACLip, 30 TLZ, 20 TLS, and 13 ST4 alone). For the implants tested with femur and graft, the mean ± standard deviation (SD) overall elongation at 250 N after cycling was 5.2 ± 0.2 mm, 8.4 ± 2.1 mm, and 5.3 ± 0.8 mm, the mean ± SD ultimate load to failure was 736 ± 116 N, 830 ± 204 N, and 640 ± 242 N, and the mean ± SD stiffness at the 1000th cycle was 185 ± 15 N/mm, 172 ± 19 N/mm, and 178 ± 21 N/mm for ACLip, ToggleLoc™, and TLS devices, respectively. There was no significant difference between the implants except for post-cycling elongation between TLZ and the other two implants (p < 0.05).

CONCLUSION

The choice of femoral fixation device plays a decisive role in controlling the overall lengthening of an ACL reconstruction using a short hamstring graft. All implants validated the specifications in terms of ultimate load to failure, the TLS system had, however, a low performance limit. ToggleLoc™ with adjustable loop should no longer be used on the femur side; instead the other types of fixation should be used to improve the overall elongation control.