Femoral suspension devices for anterior cruciate ligament reconstruction: Do adjustable loops lengthen?

Background: Cortical suspension devices are commonly used for femoral graft fixation during anterior cruciate ligament (ACL) reconstructive surgery. Adjustable-length fixation devices provide technical advantages over fixed-length loops but may be more susceptible to lengthening during cyclic loading. Hypothesis: Both fixed-length and adjustable-length femoral cortical suspension devices would withstand ultimate loads greater than those normally experienced by the native ACL and would prevent clinically significant lengthening during prolonged cyclic loading. Study Design: Controlled laboratory study. Methods: Mechanical testing was performed on 3 ACL graft cortical suspensory devices by use of an extended cyclic loading (4500 cycles at 10-250 N) and pull-to-failure protocol. Two adjustable-length devices were additionally tested with the free suture ends tied. Results: Total displacement after 4500 cycles of tensioning at variable loads (expressed as mean 6 SD) was 42.45 mm (67.01 mm) for the Arthrex TightRope RT, 5.76 mm (60.35 mm) for the Biomet ToggleLoc, and 1.34 mm (60.03 mm) for the Smith & Nephew EndoButton CL Ultra (P<.001). The Arthrex TightRope reached clinical failure of 3 mm lengthening after fewer cycles (1349 6 316) than the Biomet ToggleLoc (2576 6 73) (P<.001). The Smith & Nephew EndoButton did not reach clinical failure during cyclic testing. With the free suture ends tied, after 4500 cycles, the Arthrex TightRope had a significant decrease in lengthening to 13.36 6 1.86 mm (P<.037) There was also a significant difference in ultimate load between the TightRope (809.11 6 52.94 N) and the other 2 constructs (P<.001). Conclusion: The ultimate load of all graft-fixation devices exceeded the forces likely to be experienced in a patient's knee during the early postoperative rehabilitation period. However, the adjustable-length fixation devices experienced a clinically significant increase in loop lengthening during cyclic testing. This lengthening is partially caused by suture slippage into the adjustable-length loop. Clinical Relevance: Adjustable-length ACL graft cortical suspension devices lengthen under cyclic loads because free suture ends are pulled into the adjustable loop. This may allow for graft-fixation device lengthening during the acute postoperative period.