Arthroscopic knots: Determining the optimal balance of loop security and knot security

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Abstract

Purpose: The purpose of this study was to determine the optimal knot configuration that maximized both knot and loop security when tied with 2 different types of nonabsorbable, braided suture. Type of Study: In vitro biomechanical study. Methods: Six commonly used arthroscopic sliding knots (Duncan loop, Nicky’s knot, Tennessee slider, Roeder knot, SMC knot, Weston knot) with and without a series of 3 reversing half-hitches on alternating posts (RHAPs) as well as a static surgeon’s knot were tied. Two different nonabsorbable, braided sutures were used, and a total of 7 knots were tied for each possible combination of knots and sutures, for a total of 182 knots. Each knot was tied around a 30-mm circumference post to assure a consistent loop circumference of 30 mm before “locking” the complex sliding knots by tensioning the wrapping limb of the suture. Each loop was mounted on a Material Testing System machine, and its circumference was measured at a 5-N preload to assess each knot’s ability to maintain a tight suture loop without slippage (loop security). Knot security was measured as the maximum force to failure at 3 mm of crosshead displacement or suture breakage during single-pull load testing. Results: The surgeon’s knot provided the highest force to failure and the tightest loop circumference whether tied with No. 2 Ethibond (Ethicon, Somerville, NJ) or No. 2 Fiberwire (Arthrex, Naples, FL) suture. Among the sliding knots, the Roeder knot with 3 RHAPs showed the best balance of loop security and knot security when tied with No. 2 Ethibond or No. 2 Fiberwire. Sliding knots tied without RHAPs showed low force to failure and loose suture loops whether tied with Ethibond or Fiberwire. The addition of 3 RHAPs improved knot security and, in most cases, loop security of all the sliding knots. When tying a static surgeon’s knot or a sliding knot with RHAPs, using No. 2 Fiberwire increased the force to failure over comparable knots tied with No. 2 Ethibond. All knots failed by a combination of knot slippage and suture stretch. When using No. 2 Ethibond, securing most sliding knots with 3 RHAPs or tying a surgeon’s knot changed the failure mechanism from knot slippage to suture stretch, suggesting that the maximum knot holding capacity of No. 2 Ethibond had been achieved when tying these knot configurations. However, even at failure forces twice that achieved with No. 2 Ethibond, suture slippage continued to occur with sliding knots with 3 RHAPs using No. 2 Fiberwire. This indicates that the maximum knot-holding capacity of No. 2 Fiberwire had not been achieved, and that further knot configurations should be tested. Conclusions: (1) A static surgeon’s knot provides the best balance of loop security and knot security within the knot configurations tested in this study. (2) A sliding knot without RHAPs has both poor loop security and knot security and should not be tied. (3) The addition of 3 RHAPs improves knot security of all sliding knots tested and improves loop security of most of the sliding knots tested. (4) The addition of 3 RHAPs improves the knot security of all sliding knots to adequately resist predicted in vivo loads. (5) The Roeder knot with 3 RHAPs provides the best balance of loop security and knot security within the sliding knot configurations tested in this study regardless of suture type. (6) Tying a surgeon’s knot or a sliding knot with 3 RHAPS using No. 2 Fiberwire increases knot security over the same knot tied with No. 2 Ethibond. Clinical Relevance: This study identifies the static and sliding configurations of commonly used arthroscopic knots in order to aid the surgeon in choosing the most biomechanically effective knot for use in arthroscopic surgery.

Section snippets

Knot configurations and suture types

Six commonly used complex sliding arthroscopic knots were used in this study: the Duncan loop,12 Nicky’s knot,8 Tennessee slider,9 Roeder knot,3 SMC knot,5 and Weston knot4 (Fig 1A-F). A second set of knots was tied with the same 6 sliding knots as base knots secured by a series of 3 reversing half-hitches on alternating posts (RHAPs). Reversing the half-hitches and alternating the posts was performed by alternately tensioning the wrapping limbs with consecutive throws as previously described.

General results

Summaries of the force to failure of each of the sliding knots and the sliding knots secured with a series of RHAPs are shown in FIGURE 5, FIGURE 6, respectively. The surgeon’s knot is included in each figure as a reference. In all cases, no knots failed by suture breakage, suggesting that all knots failed by a combination of knot slippage and suture elongation.

Summaries of the loop circumference of each of the sliding knots and the sliding knots secured with a series of RHAPs are summarized

Discussion

Optimization of both knot security15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26 and loop security2, 19 for any given knot is critical, and recommendations regarding a specific knot should not be made without taking both characteristics under consideration. In this study, the loop security of almost all sliding knots tied without RHAPs (except the Duncan loop tied with No. 2 Fiberwire) was poor. Indeed, at a preload of only 5 N, many of the loop circumferences tied with No. 2 Ethibond were

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