Graft-bone motion and tensile properties of hamstring and patellar tendon anterior cruciate ligament femoral graft fixation under cyclic loading

Purpose: To assess longitudinal graft-bone motion and tensile properties of the femur-anterior cruciate ligament (ACL) graft fixation-ACL graft complex based on the hypothesis that there is little difference in graft-bone motion between suspensory and aperture hamstring ACL femoral graft fixation techniques, and between hamstring and patellar tendon ACL femoral graft fixation techniques. Type of Study: In vitro biomechanical study using human cadavers. Methods: The distal femur-ACL graft fixation-ACL graft complex was cyclically loaded between 50 and 250 N at 1 Hz for 1,000 cycles with the direction of the load applied parallel to the axis of the femoral bone tunnel. Graft-bone motion was measured indirectly using retroreflective markers and a video motion-analysis system. Tensile testing to failure was performed at 1 mm/sec for fixation techniques completing 1,000 cycles without fixation failure. Results: Among the hamstring fixation techniques, 4 of 13 Bio-Interference screws (Arthrex, Naples, FL), 2 of 12 LinX HT fasteners (DePuy Mitek, Norwood, MA), and 1 of 11 TransFix cross-pins (Arthrex) failed before completing 1,000 cycles. Five of 13 patellar tendon grafts fixed with metal interference screws, and 2 of 12 patellar tendon grafts fixed with a plastic button and No. 5 sutures failed before completing 1,000 cycles. Suture/button fixation of patellar tendon grafts resulted in significantly more graft-bone motion than hamstring tendon grafts fixed using the Bone Mulch Screw (Arthrotek, Warsaw, IN), or interference screw fixation of patellar tendon and hamstring grafts. Otherwise, there was no significant difference in graft-bone motion among the various hamstring fixation techniques or the various hamstring fixation techniques and interference screw fixation of patellar tendon grafts. Maximum graft-bone displacement after cyclic loading was significantly greater for hamstring grafts fixed with the EndoButton and EndoButton Tape (Smith & Nephew Endoscopy, Andover, MA) compared with the other hamstring fixation techniques and interference screw fixation of patellar tendon grafts. All fixation techniques except hamstring tendon grafts fixed with the Bio-Interference screw achieved at least 59% of maximum graft-bone displacement after 20 cycles. Hamstring tendon grafts fixed with the EndoButton CL were significantly stronger than all other hamstring and patellar tendon fixation methods. Patellar tendon grafts fixed with interference screws and hamstring tendon grafts fixed with interference screws and the Bone Mulch Screw and TransFix were significantly stiffer than hamstring tendon grafts fixed with the EndoButton CL. Conclusions: There is no significant difference in graft-bone motion between aperture and suspensory femoral fixation methods when the stiffness of the femur-ACL graft fixation-ACL graft complex is similar. Clinical Relevance: The small differences in graft-bone motion reported in our study provide further evidence that graft-tunnel motion or the so-called bungee effect is unlikely to be the primary cause of radiographic bone tunnel enlargement following ACL reconstruction.