Beyond the square knot: A novel knotting technique for surgical use

Sixteen surgical knot configurations were described by Heraklas in the first century AD1. Heraklas’ “Hercules” knot is recognized as the “square” or “reef” knot commonly used today. This knot and its double-loop first-throw variant, the surgeon’s knot, have been the gold standard of surgical knots for tissue repair, ligature, and wound closure for nearly a century2,3. Despite the primacy given to the square knot and its variants, knot holding strength (i.e., the force required for the knot to unravel [untie] or for the suture to break at the knot site) has been an important research topic for many years3-7. Adequate knot holding strength is essential to maintain wound closure and ensure tissue contact for healing. Knot unraveling can lead to severe complications, especially in the setting of internal tissue repairs that cannot be directly observed or monitored before catastrophic failure. Knot holding strength is especially important for high-tension closures, such as herniorrhaphy, capsular closure, and tendon and ligament repairs8-12. Knot holding strength is extremely important for flexor tendon repair, as these small structures can only provide purchase for one or two sutures and as the repair bears a high tensile force during postoperative rehabilitation. Recent studies have shown that, despite the best modern techniques of knot positioning and tying, knots unravel following flexor tendon repair as frequently as 71% to 86% of the time, depending on the repair technique13. The typical recommendation for circumventing this problem has been to increase the number of knot throws13,14. However, increasing the number of throws increases bulk, which can be a problem with certain repairs, especially the repair of flexor tendons, which must pass through a narrow fibro-osseous pulley. In addition, a large knot placed between cut tendon ends potentially interferes with the healing process and could decrease repair strength15,16. Modern high-strength suture materials cannot be used to their full advantage without proper knot holding strength, and many of these newer materials have a low coefficient of friction and are thus more likely to slip when tied17-19. Silva et al. studied the frictional coefficient of several suture materials and found that braided polyblend suture had a lower frictional coefficient than polyester or nylon sutures20. Waitayawinyu et al. reported that braided polyblend suture increased flexor tendon repair strength. However, braided polyblend knots unraveled before they broke or pulled out during 79% of failure tests13. We recently designed a 3-throw knot involving a combination of a two-strand-overhand knot plus two surgical square knots, which we have named the “TSOL” (two-strand-overhand locking) knot. The purpose of this study was (1) to measure the TSOL knot holding strength compared with that of a standard surgical 4-throw square knot with use of different suture materials, (2) to compare the TSOL knot holding strength with that of other commonly employed surgical knots, and (3) to investigate the strength of flexor tendon repairs with a TSOL knot compared with a standard square knot. We hypothesized that, compared with the square knot, the TSOL knot would have increased knot holding strength, regardless of the suture material, and would yield increased strength of repaired tendons.