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Beyond the Square Knot: A Novel Knotting Technique for Surgical Use
Chunfeng Zhao, MD1; Chung-Chen Hsu, MD1; Tamami Moriya, MD1; Andrew R. Thoreson, MS1; Steven S. Cha, MS1; Steven L. Moran, MD1; Kai-Nan An, PhD1; Peter C. Amadio, MD1
1 Biomechanics Laboratory, Department of Orthopaedics (C.Z., C.-C.H., T.M., A.R.T., S.L.M., K.-N.A., P.C.A.), and Biomedical Statistics and Bioinformatics (S.S.C.), Mayo Clinic, 200 First Street S.W., Rochester, MN 55905. E-mail address for C. Zhao: zhaoc@mayo.edu
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Investigation performed at the Mayo Clinic, Rochester, Minnesota

Disclosure: One or more of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of an aspect of this work. In addition, one or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.

Copyright © 2013 by The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2013 Jun 05;95(11):1020-1027. doi: 10.2106/JBJS.K.01525
The erratum to this article has been published | view the erratum
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This article was updated on September 25, 2013, because of a previous error. Figures 1, 2, and 7, which had previously shown a granny knot as the top portion of the TSOL knot, now show a square knot as the top portion.


Knot holding strength is essential to maintain wound closure and ensure tissue contact for healing. Knot unraveling can lead to severe complications, especially for high-tension closures such as tendon repairs, which have recently been reported to have knot unraveling rates as high as 86%. In the current study, a novel surgical knot, the two-strand-overhand locking (TSOL) knot, was designed and mechanically evaluated with use of different suture materials and knot configurations and in actual tendon repairs.


The knot holding strength of the TSOL knot was compared with that of a 4-throw square knot with use of three different suture materials that are in common clinical use. With use of braided polyblend suture, the TSOL knot was also compared with five other surgical knot configurations. Finally, the strength of tendon repairs performed with use of the TSOL knot and a 4-throw square knot was studied.


Compared with the 4-throw square knot, the holding strength of the TSOL knot was 143% greater for braided polyblend, 216% greater for polydioxanone, and 118% greater for polyester suture, with a significantly lower knot unraveling rate compared with that of the 4-throw square knot regardless of suture material. The TSOL knot holding strength was also greater than that of the other surgical knot configurations. The strength and stiffness of tendon repairs with a TSOL knot were significantly increased over those of repairs with a 4-throw square knot.


The TSOL knot provided superior knot holding strength compared with some commonly used surgical knots.

Clinical Relevance: 

The TSOL knot has potential clinical applications, especially when knot security is important and high loads are expected, as in tendon or ligament repairs.

Figures in this Article
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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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    Chunfeng Zhao MD, Steven L. Moran MD, Kai-Nan An PhD, Peter C. Amado MD
    Posted on September 11, 2013
    Risk of strangulation following tendon repair relates to suture loop configuration and repair tension, but not knot security
    Orthopedic Biomechanics Laboratory, Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN USA

    Dr. Meiss makes a good point -- any suture that can be snugged down can be over tightened, or be tied too loosely. Knowing the happy medium is the key, especially for sutures tied in tissue that will experience more tension postoperatively than it does when the knot is finally secured. Tendon repairs suffer from both problems: knots can be too tight, causing bunching and strangulation, or too loose, resulting in a gap. However, tendon strangulation has nothing to do with knot type or knot security. The potential for strangulation is related to the suture loops that grasp the tissue being sutured, and the tension under which the knot is secured[1,2]. Suture techniques have been designed to minimize strangulation, even when a knot is placed under high tension[3-5]. The purpose of the knot is to secure the repair, and to fix the tissue at the desired tension, without loosening. A knot can be tied without any tension or even with a gap, to avoid strangulation; or a knot can be tied to maintain a desired amount of tension.

    We agree with Dr. Meiss that the strangulation problem is less of a problem in hard tissues than in soft ones, for the simple reason that hard tissues are unlikely to be deformed by the suture. We disagree though that any one type of knot, such as the TSOL, is preferable in bone as opposed to soft tissue as a result. Regarding the second comment about knot configurations in our study, we described the groups C and D in the text as “…a 1-throw surgeon’s knot with a 2-throw square knot (group C), a 1-throw surgeon’s knot with a 3-throw square knot…”, which is a verbal description of Dr. Meiss’ classification. We believe that either representation is acceptable.

    Finally, we would like to alert readers to an error that another reader noted, post publication, in Figures 1, 2 and 7, which depict, incorrectly, a granny knot instead of a square knot in the drawing of TSOL knot. We have corrected this error in new figures, which will appear soon in JBJS.

    Once again, we thank Dr. Meiss for his careful review of our work and his thoughtful input.

    1.  Lee H. Double loop locking suture. J Hand Surg. 1990(15A):953-58.
    2.  Lawrence TM, Davis TR. Locking loops for flexor tendon repair. Ann R Coll Surg Engl 87(5):385-6. 2005 Sep;87(5):385-6.
    3.  Becker H, Orak F, Duponselle E. Early active motion following a beveled technique of flexor tendon repair: report on fifty cases. J Hand Surg [Am]. 1979;4(5):454-60.
    4.  Papandrea R, Seitz WH, Jr., Shapiro P, Borden B. Biomechanical and clinical evaluation of the epitenon-first technique of flexor tendon repair. J Hand Surg [Am]. 1995;20(2):261-6.
    5.  McLarney E, Hoffman H, Wolfe SW. Biomechanical analysis of the cruciate four-strand flexor tendon repair. J Hand Surg [Am]. 1999;24(2):295-301.

    A. Ludwig Meiss
    Posted on August 26, 2013
    Configuration of the TSOL knot. Risk of strangulation. Surgeon's knot with additional throws.
    Orthopaedicum-Hamburg, Hamburg, Germany

    It is well known that the security of a suture in vivo depends on the strength of the suture material and the quality of the knot, on the amount of stress (load) under function, and on the tissue strength. The latter may deteriorate by impairment of vascularity (e.g. through strangulation). Thus, necrosis of flexor tendon ends may occur which will lead to a suture insufficiency in spite of the best knot.

    According to Fig. 7, the first two-strand overhand knot of the TSOL knot can be slid, which allows an increase of tension for the approximation of the tissue ends in a comfortable way. There is a risk of overtightening, however, leading to strangulation. This risk needs to be addressed in order to avoid poor results with this interesting new knot, which is in competition with known locking sliding knots (Meiss 1985). It may follow that the TSOL knot is better suited for sutures of osseous fragments than flexor tendon ends.

    The knots in Fig. 2, C and D should be termed surgeon's knot with one/two additional square knot type throw(s) (2=1=1 and 2=1=1=1, respectively).

    Meiss L. A new, fast surgical knot for skin closures. Plast Reconstr Surg. 1985;75:428-9.

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