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

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 su