Biomechanical comparisons of current suspensory fixation devices for anterior cruciate ligament reconstruction

Cortical suspensory devices are routinely used for femoral side fixation of soft tissue graft in anterior cruciate ligament (ACL) reconstruction. The purpose of this study was to evaluate the biomechanical properties of a new adjustable loop device (GraftMax®) compared with established devices (EndoButton® and TightRope®) in ACL reconstruction and to investigate whether knotting the free end of TightRope could improve biomechanical properties.

The three cortical suspensory devices (GraftMax® Button; Conmed, EndoButton® CL; Smith & Nephew, and TightRope® RT; Arthrex) were tested under cyclic load (50-250 N for 1000 cycles) and pull-to-failure conditions at 50 mm/h in a device-only setup using a tensile testing machine. The TightRope was additionally tested with its free suture ends knotted. The statistical analyses were done with one-way analysis of variance (ANOVA) and post hoc Tukey HSD tests.

There are significant differences in the load-to-failure among the devices. The EndoButton showed the highest mean failure load at 1204.7 N compared to other devices (GraftMax (914.2 N), knotted TightRope (868.1 N) and TightRope (800.1 N) (p < 0.001). The mean total displacement after 1000 cycles was 0.76 mm, 2.11 mm, 1.56 mm and 1.38 mm for the EndoButton, GraftMax, TightRope, and knotted TightRope, respectively. The EndoButton showed significantly better properties than both the GraftMax (p = 0.000) and the TightRope (p = 0.020) but not the knotted TightRope (p = n.s.) in total displacement. However, there was no significant difference between the TightRope and GraftMax (p = n.s.).

The fixed loop (EndoButton) showed significantly better mechanical properties in failure load and displacement than TightRope or GraftMax in this biomechanical study. However, the mechanical properties of the GraftMax is comparable to the TightRope. Moreover, the knotting of TightRope improved mechanical properties in total displacement more than TightRope, but not in failure load.

The biomechanical properties of the GraftMax are comparable to the TightRope. The TightRope, when knotted, shows an improvement both in load to failure and cyclic displacement, though the differences are not significant.