The Effect on Loop Elongation and Stress Relaxation During Longitudinal Loading of FiberWire in Shoulder Arthroscopic Knots

Abstract

This study examined the viscoelastic properties of 6 common arthroscopic sliding knots (Tennessee slider, Roeder knot, SMC knot, Duncan loop, Weston knot, and Nicky's knot) with 3 reversing half-hitches on alternating posts, tied with No. 2 FiberWire (Arthrex, Naples, FL). Knot configuration was designed to simulate a double-row rotator cuff repair with suture bridges. Constructs were loaded in 20-N increments to 100 N and held for 2 minutes to monitor the viscoelastic behavior in tension. Suture was also tested without tying a knot. Stress relaxation increased with loading but did not differ between knot configurations. Initial elongation was highest during the first loading to 20 N. Relaxation was greater for the Roeder knot at 20 N and for the Roeder and SMC knots at 80 N (P < .05) when compared with the loop with no knot. Elongation was greatest for the Roeder knot throughout all loads. This difference was significant at 60 N compared with the knotless loop. At 100 N, all knots showed greater elongation than the knotless loop (P < .05). Testing of suture, without any knots, accounted for more than 75% of the overall stress relaxation and loop elongation of the suture-knot construct. In our in vitro evaluation of the Tennessee slider, Roeder knot, SMC knot, Duncan loop, Weston knot, and Nicky's knot in a simulated suture bridge construct, knot configuration was not a variable that influenced elongation or stress relaxation. Overall response was primarily due to the suture itself. With the exception of the Roeder knot, relaxation was similar provided that a secure knot was formed at the time of original tying. With the evolution of surgical devices, the reliance on knots is decreasing. The results of this study suggest that using knotless techniques for securing the rotator cuff will not change the stress relaxation characteristics of the suture bridge.