Knot Security: Throws, Knot Configuration and Technique
Knot security is the ability of a tied knot to hold without slipping or untying; in bench testing a knot is classed as secure when the suture breaks before the knot slips, or when slippage stays below a set limit of about 2 to 3 mm.[1][2][7] In 710 of 720 loaded suture loops the knot, not the strand, was the point of failure, and knot strength ranged from 5% to 99% of the unknotted suture's strength across 12 knots and 12 materials.[3] Security varies with suture material and size, knot configuration, number of throws, position in the suture line and tying technique.[2][4]
Suture materials are compared on Sutures; knotless running closure is on Barbed Sutures.
Terms
| Term | Definition |
|---|---|
| Throw | One half-knot: one strand passed around the other. A surgeon's double throw wraps twice. Most studies count a double throw as one throw; Trimbos 1984 and the Romeo laparoscopic studies count each wrap separately.[1][5] |
| Square (flat, reef) knot | Successive throws in opposite rotation, written 1=1.[6] |
| Granny knot | Successive throws in the same rotation, written 1×1.[6] |
| Surgeon's knot | A double first throw followed by single throws, written 2=1 or 2=1=1.[7] |
| Post | The strand held under tension while the other strand is thrown around it. Throws laid on a post slide down it as half-hitches.[8][7] |
| Identical sliding knot | The same tying action repeated with the same hand on the same post (S=S=S).[8] |
| Nonidentical (crossed) sliding knot | Forehand and backhand throws alternated with the same hand on the same post (S×S×S).[8] |
| Parallel sliding knot | The strand held under tension is changed on each throw while the hands alternate (S//S//S).[8] |
| Blocking half-hitch | A half-hitch thrown after the active and passive strands are exchanged; it stops further sliding.[9] |
Knot notation differs between research groups: Tera and Åberg introduced a code in 1976, Trimbos and colleagues use =, × and //, the Romeo and Koninckx laparoscopic studies use H (half-knot) and S (half-hitch) with a rotation suffix, and O'Keefe and colleagues proposed a unifying nomenclature in 2025.[3][10][11][12]
Throws Needed by Suture Material
"No knot slipped" is the throw count at which every knot in the tested group held, and stayed that way at every higher count tested.
| Suture | Size | Knot | Throws at which no knot slipped | Study model (knots per group) |
|---|---|---|---|---|
| Polyglactin 910 (Vicryl) | 5-0 | Square / surgeon's | 4 / 4 | Saline-soaked bench loops loaded to 8.89 N (10)[13] |
| Polyglactin 910 (Vicryl) | 5-0 | Square / surgeon's | Square: 1 of 10 still slipped at 5; surgeon's: 5 | Saline-soaked bench loops (10)[14] |
| Polyglactin 910 (Vicryl) | 4-0 | Square / surgeon's | 5 / 4 | Saline-soaked bench loops (10)[13] |
| Polyglactin 910 (Vicryl) | 3-0 | Square / surgeon's | 5 / 3 | Saline-soaked bench loops (10)[13] |
| Polyglactin 910 (Vicryl) | 2-0 | Snug square | 3 | Serum-soaked bench loops (20)[15] |
| Polyglactin 910 (Vicryl) | 0 | Square | 3 (both 2-throw versions slipped 10 of 10) | Bench loops (10)[1] |
| Polydioxanone (PDS) | 5-0 | Square / surgeon's | 5 / 5 | Saline-soaked bench loops (10)[14] |
| Polydioxanone (PDS) | 2-0 | Snug square | 4 | Serum-soaked bench loops (20)[15] |
| Polydioxanone (PDS) | 1 | Square / surgeon's | 3 / 3 | Water-lubricated bench knots (10)[16] |
| Polyglecaprone 25 (Monocryl) | 3-0 | Square | Security plateaued at 4 (4, 5 and 6 throws did not differ) | Plasma-soaked bench loops, 2 to 6 throws[17] |
| Polyglecaprone 25 (Monocryl) | 3-0 | Square, surgeon's, granny, sliding half-hitch | None of 95 knots slipped at 4 or 5 throws | Bench loops[18] |
| Chromic gut | 2-0 | Snug square | 3 | Serum-soaked bench loops (20)[15] |
| Chromic gut | 3-0 | Square | 1 of 10 still slipped at 6 | Saline-soaked bench loops (10)[13] |
| Polypropylene | 2-0 | Square, granny, surgeon's | 3 | Saline-soaked bench loops (10)[19] |
| Polypropylene | 5-0 | Square / surgeon's | 3 / 3 (none slipped at any count tested) | Saline-soaked bench loops (10)[14] |
| Nylon | 2-0 | Snug square | 4 | Serum-soaked bench loops (20)[15] |
| Expanded PTFE | CV-4 | Square, granny / surgeon's | 7 / 6 | Saline-soaked bench loops (10)[19] |
| Expanded PTFE | CV-5, 3-0 | Modified sliding knot | No failure below 2 N at 10 or 12 throws | Cardiac chordal model (10)[20] |
| Polyethylene-core braid (FiberWire) | Not stated | Flat square | 6 | Bench (20)[21] |
| Polyethylene-core braid (FiberWire, Nespron) | USP 2 | Reef | 9 to reach 100% rupture (braided polyester: 7) | Bench[22] |
Across five materials in sizes 4-0 to #5, at least 5 flat square throws met a binomial 95% confidence interval for security of 0.84 to 1.0 and 4 throws an interval of 0.76 to 0.99; FiberWire required 6 throws at either level.[21] In a 0-gauge comparison of polyester, polydioxanone, polypropylene and polyglactin 910, knots with 4 throws came untied more often than knots with 5 or 6, and tensile strength did not differ between 4, 5 and 6 throws.[23] In 0 polyglactin 910 tied with 5 throws, cut to 3 mm tails and soaked in saline, 27 of 56 square knots and 14 of 32 surgeon's knots untied; no silk, polydioxanone or chromic knot untied in the same test.[7]
In no. 1 sutures snugged against 1 N, 2-throw square knots held 11% to 51% of the suture's breaking force (polyglycolic acid: 100%), and every knot reached the breaking force after at most two additional throws.[16]
Position in the Suture Line
The knot that ends a continuous line ties a loop of two strands to a single strand and needs more throws than an interrupted knot.
| Suture (2-0, snug square knot) | Interrupted | Start of continuous line | End of continuous line |
|---|---|---|---|
| Chromic gut | 3 | 4 | 5 |
| Polyglycolic acid (Dexon Plus) | 3 | 3 | 5 |
| Polyglactin 910 (Vicryl) | 3 | 3 | 6 |
| Polydioxanone (PDS) | 4 | 5 | 7 |
| Nylon (Ethilon) | 4 | 5 | 6 |
| Polypropylene (Prolene) | 3 | 3 | 5 |
Minimum throws at which 20 of 20 knots broke without slipping, after 24 hours in canine serum at 37 °C.[15]
- Large-gauge suture. In USP 2 polydioxanone and USP 2 and 3 polyglactin 910, start knots needed at least 6 throws and end knots at least 7 to prevent unravelling; in polydioxanone square end knots, 1 of 10 still slipped at 6 and at 7 throws and none at 8.[24]
- Coated polydioxanone. With 2-0 polydioxanone coated in plasma or fat, square start knots needed 4 throws in plasma and 5 in fat, and square end knots needed 5 in both.[25]
- Aberdeen knot. An Aberdeen knot of 3 throws and 1 turn was secure in plasma- and fat-coated polydioxanone.[25] In a separate study, 3 throws and 2 turns gave the strongest Aberdeen knot, and adding throws or turns did not increase strength.[26]
Surgeon's Knot Versus Square Knot
- 5-0 polyglactin 910. A 3-throw square knot slipped in 10 of 12 tests; 3-throw knots that included a surgeon's double throw did not, and a 3-throw surgeon's knot had the same tensile strength as a 5-throw single-throw knot.[27]
- 3-0 to 5-0 sutures. Square and surgeon's knots generally needed 4 throws and sliding knots 5; 3-0 polyglactin 910 surgeon's knots were secure at 3 throws, against 5 for square knots.[13]
- 0 polyglactin 910. The 2=1 surgeon's knot slipped in 6 of 10 tests and the 2=2 knot in none.[1]
- 0-gauge sutures, 5 throws. Failure load and the rate of untying did not differ between surgeon's and square knots.[7]
- Dry laparoscopic bench knots in 2-0 polyglactin 910. The surgeon's flat knot (H2H1s) opened below 10 N in 5% of tests; 97.5% of symmetric H2H2 knots and 100% of asymmetric H2H2 and both H3H2 orientations met the study's no-opening-below-30 N criterion.[5]
Sliding Knots and Post Switching
A sliding knot forms whenever one strand is held under more tension than the other; each throw then runs down the tensioned strand. Its security depends mainly on whether successive throws repeat the same action and whether the post is changed.
| 3-0 suture, 5 throws | Identical (same post, same action) | Nonidentical (same post, alternating forehand and backhand) | Parallel (post changed each throw) |
|---|---|---|---|
| Polyglactin 910 (Vicryl), loop holding capacity[8] | 10.8 N | 34.0 N | 58.4 N |
| Four braided absorbables, loop holding capacity[8] | 3.2 to 11.4 N | 18.6 to 37.6 N | 50.4 to 59.3 N |
| Polyglactin 910 (Vicryl), knots slipping more than 2 mm[10] | 80% | 20% | 0% |
| Polydioxanone (PDS), knots slipping more than 2 mm[10] | 70% | 0% | 0% |
Loop holding capacity from van Leeuwen 2012 and slippage from Trimbos 1986; 10 knots per group in both.
- Throw count with identical throws. Identical sliding knots of 5 throws slipped in 40% to 80% of tests in four of five materials; parallel 5-throw knots never slipped in any of the five.[10]
- Throw count with nonidentical throws. In 0 and 2-0 polydioxanone and polyglactin 910, 3-throw nonidentical sliding knots untied in 50% to 90% of tests and 6-throw knots in 20% to 30%.[28] In 0 and 2-0 glycomer 631 monofilament, 8 of 20 and 9 of 20 nonidentical 6-throw knots untied against none of the parallel knots, and 1 or 2 of 20 nonidentical knots still untied at 10 throws.[29]
- Square knots versus sliding knots. Three-throw sliding knots and two-throw square and surgeon's knots performed poorly; in smaller-diameter sutures, sliding knots with one extra throw performed the same as square knots.[30]
- Blocking half-hitches. In 0 polyglactin 910, two sliding half-hitches followed by one blocking half-hitch held 52 N or 98 N depending on the rotation of the throws; with a second asymmetric blocking half-hitch every suture broke, and with a second symmetric blocking half-hitch 8 of 10 knots slid open.[9]
- Monofilament sequences. In tensiometer testing, secure monofilament knots needed 6 throws (two symmetric sliding half-hitches and four asymmetric blocking half-hitches), whereas 4- or 5-throw sequences were secure with braided sutures.[6][11] Five half-hitches with three blocking throws (SSSbSbSb) were recommended for laparoscopic use.[31]
- Alternating posts. A systematic review of 14 studies found knots with throws on alternating posts more secure and less variable than knots with opposite throws on the same post.[32] Arthroscopic sliding knots are backed up with reversed half-hitches on alternating posts; in braided polyester, SMC, Field and Giant sliding knots resisted cyclic loading after 1 additional half-hitch and the Duncan loop after 2.[33]
- Trainee knots. Of knots tied by 25 surgical trainees, 12.6% in Vicryl and 5.6% in Prolene opened below 5 N, and every one of these was a slip knot of up to 6 throws.[34]
Tying Technique
- Tying force. In USP 2 polydioxanone, 5-throw square knots held when each throw was set with 5 N or more; 2 of 7 failed at 1 or 2 N and 7 of 7 at 0.5 N. Polyethylene-core 5-throw knots resolved in every test even at 50 N per throw.[35]
- Pulling direction. In 3-0 silk tied by 368 residents, knots laid by pulling in alternate directions were stronger at every count from 2 to 7 throws; at 7 throws, 7.7% of alternately pulled knots untied against 19.6% of knots pulled in a constant direction.[36]
- Traction. In laparoscopic testing, tying each knot with higher traction increased the security of half-knot and half-hitch sequences.[31]
- Laparoscopic versus hand tying. In knots tied in fresh postmortem human stomach, three half-hitches and surgeon's knots tied laparoscopically were weaker than the same hand-tied knots, and an additional throw increased security; hand-tied knots needed 4 half-hitches in nylon, polytetrafluoroethylene, braided polyester suture and polyamide and 3 in polyglactin 910, braided polyester fiber, silk and polydioxanone.[37]
- Fluid. DynaCord needed 6 throws dry, 4 wet and 5 in fat to rupture without unravelling, against 7 in all three conditions for FiberWire.[38]
Knot Bulk
- Volume and weight. In USP 2 polydioxanone square start knots, mean knot weight increased from 20.3 milligrams at 4 throws to 32.0 milligrams at 8.[24]
- Extrusion. In a swine subcuticular model with 4-0 braided absorbable surgeon's knots, cumulative suture extrusion over 5 weeks was 17% with 3 throws, 10% with 4 and 30% with 5 in lactomer (Polysorb), and averaged 31% in coated polyglactin 910 against 19% in lactomer.[39]
- Reviews. A review of 86 studies reported 3 to 5 throws for square and surgeon's knots, 3 throws with 1 or 2 turns for the Aberdeen knot, and an optimal tail length of 3 mm.[4]
See Also
References
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2. Wong YR, McGrouther DA. "Biomechanics of surgical knot security: a systematic review." Int J Surg. 2023;109(3):481-490. doi:10.1097/JS9.0000000000000298
3. Tera H, Aberg C. "Tensile strengths of twelve types of knot employed in surgery, using different suture materials." Acta Chir Scand. 1976;142(1):1-7. PMID 1266536
4. Bushong EE, Janis JE. "Knot Security 101: A Comprehensive Practical Review to Optimal Knot Configuration, Pulling Direction, Throw Count, and Tail Length." Plast Reconstr Surg Glob Open. 2024;12(8):e6047. doi:10.1097/GOX.0000000000006047
5. Romeo A, Rocha CL, Fernandes LF, et al. "What is the Best Surgeon's Knot? Evaluation of the Security of the Different Laparoscopic Knot Combinations." J Minim Invasive Gynecol. 2018;25(5):902-911. doi:10.1016/j.jmig.2018.01.032
6. Romeo A, Fujimoto C, Cipullo I, et al. "Effect of Diameter and Type of Suture on Knot and Loop Security." J Clin Med. 2023;12(19):6418. doi:10.3390/jcm12196418
7. Muffly TM, Boyce J, Kieweg SL, Bonham AJ. "Tensile strength of a surgeon's or a square knot." J Surg Educ. 2010;67(4):222-6. doi:10.1016/j.jsurg.2010.06.007
8. van Leeuwen N, Trimbos JB. "Strength of sliding knots in multifilament resorbable suture materials." Gynecol Surg. 2012;9(4):433-437. doi:10.1007/s10397-012-0753-5
9. Romeo A, Cipullo I, Kondo W, et al. "The importance of rotation to teach secure half-hitch sequences in surgery." Facts Views Vis Obgyn. 2023;15(4):317-324. doi:10.52054/FVVO.15.4.101
10. Trimbos JB, Van Rijssel EJ, Klopper PJ. "Performance of sliding knots in monofilament and multifilament suture material." Obstet Gynecol. 1986;68(3):425-30. doi:10.1097/00006250-198609000-00029
11. Koninckx PR, Ussia A, Wattiez A, Kondo W, Romeo A. "Laparoscopic Surgery: A Systematic Review of Loop and Knot Security, Varying with the Suture and Sequences, Throws, Rotation and Destabilization of Half-Knots or Half-Hitches." J Clin Med. 2023;12(19):6166. doi:10.3390/jcm12196166
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18. Avoine X, Lussier B, Brailovski V, Inaekyan K, Beauchamp G. "Evaluation of the effect of 4 types of knots on the mechanical properties of 4 types of suture material used in small animal practice." Can J Vet Res. 2016;80(2):162-70. PMID 27127344
19. Dang MC, Thacker JG, Hwang JC, Rodeheaver GT, Melton SM, Edlich RF. "Some biomechanical considerations of polytetrafluoroethylene sutures." Arch Surg. 1990;125(5):647-50. doi:10.1001/archsurg.1990.01410170095020
20. Miller JR, Deeken CR, Ray S, et al. "Expanded Polytetrafluoroethylene for Chordal Replacement: Preventing Knot Failure." Ann Thorac Surg. 2015;100(6):2325-9. doi:10.1016/j.athoracsur.2015.07.089
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29. Ivy JJ, Unger JB, Mukherjee D. "Knot integrity with nonidentical and parallel sliding knots." Am J Obstet Gynecol. 2004;190(1):83-6. doi:10.1016/s0002-9378(03)00947-5
30. van Rijssel EJ, Trimbos JB, Booster MH. "Mechanical performance of square knots and sliding knots in surgery: comparative study." Am J Obstet Gynecol. 1990;162(1):93-7. doi:10.1016/0002-9378(90)90828-u
31. Romeo A, Fernandes LF, Cervantes GV, et al. "Which Knots Are Recommended in Laparoscopic Surgery and How to Avoid Insecure Knots." J Minim Invasive Gynecol. 2020;27(6):1395-1404. doi:10.1016/j.jmig.2019.09.782
32. O'Keefe TJ, Lake C, Perkins LA, et al. "'The Gordian knot of it he will unloose': Lessons learned from studies of half-hitch surgical knots and implications for practicing surgeons: A systematic review." Surgery. 2025;178:108932. doi:10.1016/j.surg.2024.10.023
33. Kim SH, Yoo JC, Wang JH, Choi KW, Bae TS, Lee CY. "Arthroscopic sliding knot: how many additional half-hitches are really needed?" Arthroscopy. 2005;21(4):405-11. doi:10.1016/j.arthro.2004.12.010
34. Ching SS, Mok CW, Koh YX, Tan SM, Tan YK. "Assessment of surgical trainees' quality of knot-tying." J Surg Educ. 2013;70(1):48-54. doi:10.1016/j.jsurg.2012.07.002
35. Neuhofer S, Wieser K, Lajtai G, Müller D, Gerber C, Meyer DC. "Surgical knot tightening: how much pull is necessary?" Knee Surg Sports Traumatol Arthrosc. 2014;22(11):2849-55. doi:10.1007/s00167-013-2452-9
36. Guo HF, Hou XY, Dai WW, Liao DZ, Wen C. "Influence of pulling direction on knot security: A laboratory research." Asian J Surg. 2024;47(1):420-424. doi:10.1016/j.asjsur.2023.09.058
37. Kadirkamanathan SS, Shelton JC, Hepworth CC, Laufer JG, Swain CP. "A comparison of the strength of knots tied by hand and at laparoscopy." J Am Coll Surg. 1996;182(1):46-54. PMID 8542089
38. van Knegsel KP, Zderic I, Kastner P, et al. "Knot holding capacity of two different high-strength sutures-a biomechanical analysis." Int Orthop. 2024;48(3):643-649. doi:10.1007/s00264-023-06041-z
39. Drake DB, Rodeheaver PF, Edlich RF, Rodeheaver GT. "Experimental studies in swine for measurement of suture extrusion." J Long Term Eff Med Implants. 2004;14(3):251-9. doi:10.1615/jlongtermeffmedimplants.v14.i3.90