Introduction

Suture tying is a fundamental skill required in all surgical specialties. Knot and suture integrity is essential to safely carry out various aspects of surgery, such as hemostasis, anastomosis, tissue closure, or securing medical lines and devices. The integrity of a suture loop is dependent on multiple factors, the knot is the weakest part of the loop and therefore its strength and integrity is of utmost importance. [1,2] A square knot technique is one of many knots used in surgery. [3] A square knot has been shown to be most reliable when it is applied correctly using a technique where the surgeon’s hands cross each other at 180 degrees with each throw. [3-5] If this is not done properly an inadvertent slip knot is formed despite a ‘square knot’ configuration, leading to increased knot slippage. ⁵ Our research study aims to determine the minimum number of throws needed, when applied via a proper square knot technique, to secure various types of commonly used sutures in surgery. We also set out to determine whether suture material and gauge influence the number of throws needed for knot security.

Materials and Methods

Five commonly used absorbable sutures were individually tested in this study 0 and 4-0 Vicryl (Polyglactin 910), 3-0 Monocryl (Poliglecaprone 25) and 0 and 3-0 PDS (Polydioxanone). Ten tests for each suture were carried out with three, four and five throws using a square knot technique applied via hand tying onto a tensioning device, ensuring that a correct technique with crossing over of hands was used. Even distracting tension was then applied to the suture to test the knot. A ‘secure knot’ result was achieved when the tension applied resulted in fracture of the suture prior to slippage of <2mm from the center-point of the knot. Difference of proportions test was performed between four and five throws to determine whether a statistical difference was achieved with the fifth throw.

Results

All suture loops behaved similarly regardless of type and gauge. Suture loops secured with only three square throws all slipped and failed tension testing. Test results using four and five throws are listed in Table 1. Suture loops secured using four square throws were found to be adequately secured (average 10% failure rate). Total loop security was achieved when five throws were used (0% failure rate). No statistical difference was found between using four or five throws.

^† all loops secured using 3 throws slipped and failed testing, and therefore were not included in analysis and this table.

^‡ out of 100 tests. 

Table 1: Suture loop testing using 4 or 5 throws^†.

Discussion

Knot tying is an integral part of competency. Loop security is dependent on many factors, including suture tensile strength, knot type, and surgical technique. A square knot, when applied correctly, has been shown to be amongst one of the strongest surgical knots. [3-5] Our study shows that square knot integrity and strength is independent of suture type or size. When using a proper square knot technique, a minimum of four throws are required for adequate loop security. An additional fifth throw is optional to ensure absolute security.

References

1. Tera H, Aberg C (1976) Tensile strengths of twelve types of knot employed in surgery, using different suture materials. Acta Chir Scand 142: 1-7.
2. van Leeuwen N, Trimbos JB (2012) Strength of sliding knots in multifilament resorbable suture materials. Gynecol Surg 9: 433-437.
3. Trimbos JB (1984) Security of various knots commonly used in surgical practice. Obstet Gynecol 64: 274-280.
4. Brouwers JE, Oosting H, de Haas D, Klopper PJ (1991) Dynamic loading of surgical knots. Surg Gynecol Obstet 173: 443-448.
5. Drabble E, Spanopoulou S, Sioka E (2021) How to tie dangerous surgical knots: easily. Can we avoid this?. BMJ Surg Interv Health Technol 3: e000091.