To tie or not to knot: How the Half Instrument Tie Technique Outdoes the Traditional Surgeon's Knot
Ronald K. Akiki, MD, Vinay Rao, MD, MPH, Mimi R. Borrelli, MD, Dardan Beqiri MD, Paul Y. Liu, MD
Department of Plastic Surgery, Alpert Medical School at Brown University, Providence, Rhode Island
Background: Despite the widely acknowledged advantages to the surgeon’s knot technique, there are drawbacks to consider. The second throw in a surgeon’s knot creates an acute angulation of the suture which creates a gap between each suture. This decreases knot security and prevents sufficient advancement. The outcome is a bulky knot at risk of gapping and obstructing complete approximation of wound edges. Decreased loop security, defined as the ability to maintain a tight suture loop as a knot is tied, is also an inherent risk of surgeon’s knots and may further prevent adequate tissue approximation. We propose an underappreciated alternative to the traditional surgeon’s knot; the “half instrument tie”.
Methods: Figure 1 presents its first formal description for a right-handed individual. The half instrument tie technique provides many theoretical advantages to the surgeon’s knot. First, it presents a biomechanical advantage by avoiding an additional same direction throw and thus consequently a decrease in knot advancement. Second, it is relatively simple and fast, and exploits the tension created using a pinch maneuver. Third, it provides a means by which to hold tension between the first and second throw, and thus solves the problem of potential unraveling when performing single throw square knots. For a square knot, the coefficient of friction while laying the knot is explained using the equation reported by Maddocks and Keller 1=2?e(??) Where, ? is the coefficient of friction (~0.24) while the tension required to break the knot is outlined in the equation by Reis et al n^2 h/e=1/(8?^2 ?3) g([?(96?3 ?)/??^2. (n^2 Fh^2)/B]^(1/3) ) Where, h is the suture radius, n is the number throws ( >= 1), F is the traction force, B is the bending stiffness coefficient, e is the end-to-end distance after knot Results: Comparing the surgeon’s knot to the half instrument tie using these equations provides a theoretical proof for the advantage the of the half instrument tie. A surgeon’s knot, having an increased number of throws (greater n) than the half-instrument tie, will simulate a lower traction force (lower F) and a greater end-to-end distance between wound edges (greater e). This means that the Surgeon’s knot requires less tension to break and is more likely to fail than the half instrument tie.
Conclusion: In summary, the half instrument tie is a simple new technique with significant advantages over the surgeon’s knot, providing surgeons an efficient and effective method to tie a square knot under tension.
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