Abstract
Self-locking button-like fixation devices for ACL reconstruction are attracting knee surgeons' attention due to promising technical advantages: complete filling of the tunnel with graft, anatomic reconstruction (AM portal), fixation achievement even when a short tunnel is reamed, opportunity of graft re-tensioning after tibial fixation and/or cyclic load. We compared two similar devices (TightRope vs ToggleLocZL)
20 fresh-frozen porcine femurs (mean age 2.1 years) were assigned to the two groups by randomization. Hamstrings with 9 mm of diameter were obtained using bovine tendons that show the same biomechanic behaviour of human hamstrings. Femoral tunnel was created by AM portal technique (anatomic position). Zwick-Roell z010 tension/compression device with bone and tendon clamps, was used for the study:
Cyclic test (1000 cycles, 0.5 Hz, 50–250 N/cycle, 50 cycles of preload at 10–80 N/cycle)
Final pull-out test (1 mm/s)
Failure analysis
CT scan and densitometry
Any implant didn't fail during cyclic test. The elongation average was 2.85±1.63 for ToggleLoc and 2.71±.85 for TightRope (P>0.05). Pull-out test showed different values in terms of Ultimate Strength Failure (USF), Stiffness at USF, and Stiffness:
The failure mode was:
The mean method of failure was the fracture of the cortical bone of the femoral condyle, for both groups. But if we extrapolate the USF the difference was favourable(P<0.05) for TightRope (707.83 N) than ToggleLoc (580.16).
The mean bone density of porcine femora was comparable to young human femora (1.12±0.31 BMD)
The reproducibility of surgical technique, the mechanical strength and endurance of the systems suggest two valid options for ACL reconstruction with hamstring. ToggleLoc showed worse results due to the sharp squared edges of the button.
