Evaluation of Tibial Fixation Devices for Quadrupled Hamstring ACL Reconstruction

Abstract

Background: Shortcomings to tibial-side fixation have been reported as causes of failure after anterior cruciate ligament reconstruction. Adjustable-loop suspensory devices have become popular; however, no comparison with hybrid fixation (ie, interference screw and cortical button) exists to our knowledge.

Purpose: The purpose of this study was to compare the biomechanical properties of adjustable loop devices (ALDs) in full-tunnel and closed-socket configurations in relation to hybrid fixation. We hypothesized that primary stability of fixation by a tibial ALD will not be inferior to hybrid fixation.

Study design: Controlled laboratory study.

Methods: Tibial fixation of a quadrupled tendon graft was biomechanically investigated in a porcine tibia-bovine tendon model using 5 techniques (n = 6 specimens each). The tested constructs included hybrid fixation with a cortical fixation button and interference screw (group 1), single cortical fixation with the full-tunnel technique using an open-suture strand button (group 2) or an ALD (group 3), or closed-socket fixation using 2 different types of ALDs (groups 4 and 5). Each specimen was evaluated using a materials testing machine (1000 cycles from 50-250 N and pull to failure). Force at failure, cyclic displacement, stiffness, and ability to pretension the graft during insertion were compared among the groups.

Results: No differences in ultimate load to failure were found between the ALD constructs (groups 3, 4, and 5) and hybrid fixation (group 1). Cyclic displacement was significantly higher in group 2 vs all other groups (P < .001); however, no difference was observed in groups 3, 4, and 5 as compared with group 1. The remaining tension on the construct after fixation was significantly higher in groups 3 and 4 vs groups 1, 2, and 5 (P < .02 for all comparisons), irrespective of whether a full-tunnel or closed-socket approach was used.

Conclusion: Tibial anterior cruciate ligament graft fixation with knotless ALDs achieved comparable results with hybrid fixation in the full-tunnel and closed-socket techniques. The retention of graft tension appears to be biomechanically more relevant than tunnel type.

Clinical relevance: The study findings emphasize the importance of the tension at which fixation is performed.

Keywords: anterior cruciate ligament; biomechanics; fixation; tibia.

Figure 1.

The tibial fixation devices that were tested by construct group. (A) Full-tunnel technique with hybrid fixation (1), cortical suspensory fixation for open-suture strand (2), and ALD based on a modified sling lock mechanism and extension button (3). (B) Closed-socket configuration with ALD based on a modified sling lock mechanism (4) and ALD based on a finger trap mechanism (5). ALD, adjustable loop device; CFD, cortical fixation device; FTD, finger trap device; SLD, sling lock device.

Figure 2.

(Left) Mounting of the tibia graft construct on a universal materials testing machine. The proximal end of the graft is secured to a steel hook and aligned parallel to the machine loading axis. (Right) Schematic representations of the quadrupled graft preparation techniques with either continuous loop with an adjustable loop device (groups 3, 4, and 5) or open ends (groups 1 and 2).

Figure 3.

Box plots show the results of biomechanical testing for the 5 study constructs. The middle line represents the median; the box, interquartile range; and the whiskers, the minimum and maximum values. Significant difference between groups: *P < .05. ***P < .001. ^a Significant difference vs groups 1, 2, and 5 (P < .05). CFD, cortical fixation device; FTD, finger trap device; SLD, sling lock device.

Figure 4.

Correlation of retained pretension and initial displacement of different devices. Values less than 0 (gray line) indicate that the implanted graft was still under tension after preconditioning (eg, tendon was still stretched by 0.1 mm), and values greater than 0 indicate that the construct experienced elongation. Nonlinear regression curve (R ² = 0.85) was assessed with goodness of fit (sum of squares) and positively tested for homoscedasticity. The dotted lines indicate 95% CIs. CFD, cortical fixation device; FTD, finger trap device; SLD, sling lock device.