Very strong sutures can still slip: evaluation of five knot types and two suture materials for shoulder arthroscopy (SS-47)

      Persistent defects after arthroscopic rotator cuff repair may be due to the technical challenges associated with suture loop and knot security. Very strong suture materials decrease the incidence of suture breakage during knot tying, however these materials are not automatically more reliable in regard to slippage at sub-maximal loads. The purpose of this study was (1) to compare the performance of a standard suture material (No. 2 Ethibond [Ethicon]) with a newer material (No. 2 Fiberwire [Arthrex]) in regard to knot security and load to failure using multiple arthroscopic knot configurations, and (2) to evaluate the biomechanical performance of a new sliding - locking knot compared to four surgical standards. Methods: Five knots were evaluated (Weston, Tennessee, Duncan, SMC, and the new San Diego knot) using two suture materials (No. 2 Ethibond or No. 2 Fiberwire). Ten samples were tested for each knot-suture configuration. All knots were tied by the same surgeon using an arthroscopic knot pusher. Knots were tied through a working cannula over a 38 mm diameter dowel to create loops of consistent diameter. Each knot was backed up by four reversed hitches over reversed posts. The suture loops were fixed inside a servohydraulic MTS858 machine, pre-tensioned to 10N and cycled between 10N and 45N for 1000 cycles. Intact knots were then loaded to failure. A two-way ANOVA (P < .05) with a Tukey’s post-hoc test for multiple comparisons was used for statistical analysis. Results are presented as mean ± SD. Results: Fiberwire had significantly higher load-to-failure (276 ± 24 N) compared to Ethibond (111 ± 13 N, p < .001). Overall, there was no statistically significant difference in these parameters as a function of knot configuration. However, marked sub-maximal “slippage” was noted in a subset of the knots tied with Fiberwire. Of the fifty Fiberwire knots, three failed by early slippage during cyclic load, and eight slipped at very low tension during load to failure. Early slippage was not observed with Fiberwire using the San Diego knot, and none of the Ethibond knots failed by early slippage. For knots that did not slip early, Fiberwire demonstrated approximately 50% less total loop elongation prior to failure compared to Ethibond (p < .005). Discussion: Although Fiberwire was considerably stronger than Ethibond, it also had a greater tendency for slippage at relatively low loads. This observation reflects the surface characteristics and internal construction elements that affect frictional resistance within the knot. Early slippage was not observed with the San Diego knot, which has a unique flip-loop mechanism that creates high internal knot friction. Although slippery suture is an advantage for sliding within anchor eyelets and for delivery of arthroscopic knots, it may come at a price in regard to knot security. Surgeons should understand the impact of handling characteristics, frictional properties, and ultimate failure load when selecting suture materials and knots for arthroscopic repair.