Tensile Force Applied Prior to Cutting Affects Knot Security in Small-Caliber Ultra-High Molecular Weight Polyethylene Suture.

Abstract

Given their stiffness, ultra-high molecular weight polyethylene (UHMWPE) sutures exhibit poor knot-holding capacity and are prone to unraveling. Surgeons often add extra throws to enhance knot security, leading to bulky knots, which can be problematic in procedures like flexor tendon repair. This study evaluated how different tensile forces applied to the suture ends prior to cutting affect the knot security of UHMWPE sutures. Two UHMWPE suture sizes, 3-0 and #2, were tested using an axial torsional test frame. Tensile preload forces of 2, 3, or 5 lbs were applied to the suture ends using calibrated weights before trimming at 3 mm tail length. Post-trimming, each knot was assessed visually and classified as fully unraveled, partially unraveled, or intact. A total of 120 trials were conducted, including 60 using #2 sutures and 60 using 3-0 sutures. The #2 knots exhibited no visible changes following cutting and did not unravel under any preload condition. In contrast, the 3-0 knots partially unraveled six times and completely unraveled 12 times. The frequency of 3-0 suture unraveling increased from 15% at 2 lbs to 40% at 5 lbs, indicating a tension-dependent failure pattern. Of the 48 knots that proceeded to load-to-failure testing, 45 failed via unraveling at a mean force of 29 N (95% CI: 27-35), whereas 3 failed via breakage at 77 N (95% CI: 72-82). Smaller calibers of UHMWPE suture have a greater propensity to unravel at the time of cutting as tension increases. We recommend limiting tension applied to the free suture limbs to <3 lbs prior to cutting to minimize the risk of unraveling and subsequent suture failure. Smaller-caliber UHMWPE sutures require less tension to reduce risk of knot unraveling.