Biomechanical Evaluation of an Adjustable Loop Suspensory Anterior Cruciate Ligament Reconstruction Fixation Device: The Value of Retensioning and Knot Tying

Purpose To evaluate the effects of retensioning and knot tying on the biomechanical properties of an adjustable loop anterior cruciate ligament (ACL) reconstruction device. Methods Testing consisted of 3 phases, which used both adjustable loop devices (ALD) and closed loop devices (CLD) tested under cyclic loading to 4,500 cycles. Phase 1 consisted of implant-only testing using cyclic loading from 50 to 250 N. Phase 2 used relatively unloaded cyclic loading of 10 to 250 N. Phase 3 used a tendon/bone/implant model. Subsets of the ALD implants were subjected to isolated retensioning, isolated knot tying, or a combination of both to allow for independent examination of these interventions. Results In phase 1, retensioning and knot tying reduced final ALD elongation by 60% (0.38 v 0.96 mm; P = .00004). In phase 2, retensioning and knot tying reduced final ALD elongation by 88% (0.51 v 4.22 mm, P = .014). In phase 3, retensioning and knot tying reduced final ALD elongation by 45% (1.5 v 2.7 mm; P = .001), which was half of the elongation of the CLD (3.0 mm; P = .0007). Conclusions The ALD did demonstrate an increase in cyclic elongation as compared with the CLD during both extended loading conditions. The phase 1 ALD elongation (0.96 mm), while statistically greater than the CLD (0.52 mm), was likely not of clinical importance. However, the ALD elongation in phase 2 (4.22 mm) could be of clinical concern. Both of these increased elongations were eliminated by retensioning and knot tying. Furthermore, when evaluating in a graft-femur construct, retensioning and knot tying of the ALD reduced final cyclic elongation by 50% when compared with CLD. Clinical Relevance Retensioning and knot tying after initial reduction of the tendon graft with an adjustable loop ACL fixation device may help to further reduce concerns of loop slippage and displacement with cyclic loading during postoperative rehabilitation.