Arthroscopic knot tying is a skill most orthopedic surgeons master during their training.1,2 Mastery generally comes with repetition to develop the proper feel of the appropriate suture tension when tying. For uncommon situations where the sutures have excessive tension while tying arthroscopic knots or in training situations where novice orthopedic surgeons are being taught this technique, suture breakage can be frustrating and pose a challenging dilemma. Most sutures break at the suture knot interface, causing loss of the suture as a fixation point. When using suture anchors, loss of the suture essentially is loss of the suture anchor. A technique that has suture breakage outside of the cannula where the suture can be saved and that prevents suture breakage at the suture knot can be useful during training in this arthroscopic procedure.
Recently, braided, nonabsorbable polyblend sutures have gained popularity in arthroscopic surgeries because of their superior biomechanical properties and tensile strengths compared with previous generations of suture materials, which were associated with suboptimal strength and intraoperative failure.3 Multiple studies have found that among the most commonly used braided, nonabsorbable polyblend sutures, FiberWire (Arthrex, Naples, Florida) has superior resistance to bending abrasion and superior tensile strength.4
In this study, the authors compared the maximum amount of strain across Fiber-Wire No. 2 and 2-0 sutures before failure when knot tying as well as the location of the suture break between hand tying and instrument tying, or tying with a safety clamp, needle driver. They hypothesized that use of a safety clamp would cause a weak point in the suture at the location of the clamp, thus making the suture more susceptible to breaking at said clamping point as opposed to breaking at the knot when too much tension was applied. Therefore, when surgeons are mastering the suture technique in arthroscopic surgery, a safety clamp could be useful by causing breakage of the suture at the clamping point away from the knot when too much tension is applied, thus salvaging the knot.
Materials and Methods
An experimental, comparative study of 2 suture knot tying techniques was performed. An FGV-XY digital force gauge (Shimpo Instruments, Cedarhurst, New York) was used to measure the strain across the suture at the time of its failure. The force gauge, along with its connecting hook attachment, was securely fastened to the table surface to limit artifact force measurements. Per the operator's manual, the “standard mode memory” setting of the force gauge was used to measure the peak force across the suture at the time of its failure. A FiberWire No. 2 braided polyblend suture was then fastened onto the hook attachment with a surgeon's knot followed by 2 square knots.5 One arm of the suture was strung through a knot pusher and a needle driver. The needle driver was used to hold tension while pushing the knot. The post arm was either fastened around the experimenter's hand for hand tying or clamped with a needle driver. While the knot pusher was down on the knot to serve as a counterforce, excessive force of pull was applied, both approximately 10 cm from the knot, directly back in the plane of the force gauge with the suture either wrapped around the experimenter's hand or secured with the safety clamp, post arm (Figure). Measurement of the strain across the suture was performed per the instructions provided in the operator's manual. This was then repeated using FiberWire 2-0.
The experimental setup: 1 arm of the suture was strung through a knot pusher and placed under excessive force, while the post arm of the suture was wrapped around the experimenter's left hand (A) or secured with the safety clamp (B).
FiberWire was chosen due to its utility in arthroscopic surgery. As a result of its ultra-high molecular weight polyethylene core and braided jacket of polyester ultra-high molecular weight polyethylene, FiberWire has advantages over other nonabsorbable braided sutures. It has higher failure loads and inherent ability to resist bending abrasion and tensile failure.3–7 FiberWire No. 2 and 2-0 were tested because they are among the most commonly used sutures, or anchors, during arthroscopic procedures, including anterior cruciate ligament reconstruction, rotator cuff repairs/reconstructions, and procedures related to the hand, wrist, foot, and ankle.8,9
For each type of FiberWire, 20 independent suture knot trials were conducted of both the hand tying and the safety clamp techniques, resulting in a total of 40 independent trials. The mean and standard deviation of the force causing suture failure (in Newtons) and the distance of the suture break (in centimeters) from the suture knot were recorded for both tying techniques on both types of FiberWire. Because fewer than 30 trials were performed per technique per wire type, the Wilcoxon rank sum test was used to assess for differences in the load to failure and the location of suture break between the knot tying techniques. P<.05 was considered statistically significant. In testing for differences in failure load, this study had 95% power to detect a statistically significant difference at an alpha level of 0.05 with 6 total trials on FiberWire No. 2 and 98% power to detect a statistically significant difference at an alpha level 0.05 with 2 trials on Fiber-Wire 2-0. SAS version 9.4 software (SAS Institute Inc, Cary, North Carolina) was used for all statistical and power analyses.
On reviewing the load to failure and the location of the breaks using the Wilcoxon rank sum test to compare means, the authors found significant differences between hand tying and tying with a safety clamp. For FiberWire No. 2, the mean load to failure was 142.60±2.33 N for hand tying and 78.79±1.97 N for the safety clamp (P<.0001). For FiberWire 2-0, the mean load to failure was 62.98±4.90 N for hand tying and 34.43±2.46 N for the safety clamp (P<.0001) (Table 1).
Load to Failure Results
For FiberWire No. 2, the mean location of suture breakage was 0 cm for hand tying and at the clamping point (10.45±0.34 cm) for the safety clamp (P<.0001). For FiberWire 2-0, the mean location of suture breakage was 0 cm for hand tying and at the clamping point (10.47±0.22 cm) for the safety clamp (P<.0001) (Table 2).
Location of Break Results
The suture-breaking force was significantly higher for hand tying compared with the safety clamp on both FiberWire No. 2 and 2-0. In contrast, the distance of the suture breakage from the suture knot was significantly longer for the safety clamp compared with hand tying.
One of the most frustrating aspects of arthroscopic surgery is breakage of the suture knot. This frustration is amplified at academic institutions, where future surgeons are developing mastery of the arthroscopic suture technique. Part of said mastery is developing a tactile awareness of the appropriate amount of tension when tying a suture. At the beginning of their training, it is understandable that many surgeons are unsure of the strength with which they tie their knots. Suture breakage at the knot after passage of the suture through arthroscopic anchors will compromise the entire construct, forcing surgeons to start anew. To date, there have been no studies showing the utility of a safety clamp for instrument tying when mastering the arthroscopic suture technique.
In this study, the authors compared the measured peak force under which the FiberWire suture broke and the location of the suture breakage between hand tying and instrument tying, or use of a safety clamp. Use of a safety clamp in a controlled environment in which the suture was placed under excessive force resulted in failure of the suture at the clamping point away from the knot. In contrast, hand tying with excessive force led to failure of the suture at the knot. Failure of the suture with the use of a safety clamp also occurred at a significantly lower peak force when compared with hand tying.
The data indicated the utility of a safety clamp for the training of future arthroscopic surgeons at an academic institution. In arthroscopic surgery, use of the safety clamp preserves the suture by causing its breakage at the clamping point outside of the cannula as opposed to at the knot, thus leaving enough suture tail for the surgeon to still complete the knot. Preservation of the suture ultimately avoids the cost of the wasted FiberWire and anchor construct that results when the suture fails at the knot itself.
Failure of the suture at a significantly lower peak force with a safety clamp vs hand tying also has its utility during arthroscopic surgery involving osteoporotic bone. Recent literature has revealed that a high percentage of elderly patients have significant bone mineral density deficiency at the insertion site of the rotator cuff.10,11 Poor bone quality at the location of the suture anchor coupled with the higher peak force at which the suture will fail when hand tying may result in loosing or dislodging of the suture anchor before suture failure, with the end result being compromise of the current anchor location and the entire suture anchor construct itself. It can be argued that an anchor that fails during knot tying probably should never have been placed.
This experimental design had limitations. First, tying a knot on the secured hook of a force gauge differs greatly from the in vivo atmosphere of arthroscopic surgery and cannot account for clinical variability.12,13 The force gauge was securely fastened to a table, allowing the experimenter to consistently pull with excessive force in its plane. Surgeons, however, may pull in a variety of planes on an anchor attached to a non-static surface. This experiment also failed to account for the wet environment typical of arthroscopic surgery, the quality of the tissue being anchored, and the quality of the bone in which the anchor rests.14 Second, the experiment used a surgeon's knot coupled with 2 square knots instead of an arthroscopic knot that needs to slide through the arthroscopic cannula. Several studies have tested the behavior and security of arthroscopic knots, reporting that different knots have different biomechanical performance.6,15,16 Third, as a result of the high cost of FiberWire, the experiment was limited to only 40 trials.
The findings of this study indicate the utility of a safety clamp in orthopedic education as surgeons master the arthroscopic suture technique. Use of a safety clamp preserves the suture knot when it is placed under excessive tension, thus salvaging the suture anchor construct. Given the results of the power analysis and the consistency in their results, the authors believe that these data are valid and adequately powered for the current investigation.
- Hanypsiak BT, DeLong JM, Simmons L, Lowe W, Burkhart S. Knot strength varies widely among expert arthroscopists. Am J Sports Med. 2014;42(8):1978–1984. doi:10.1177/0363546514535554 [CrossRef]
- Baumgarten KM, Wright RW. Arthroscopic Knot Tying: An Instruction Manual. Baltimore, MD: Lippincott Williams & Wilkins; 2005.
- Swan KG Jr, Baldini T, McCarty EC. Arthroscopic suture material and knot type: an updated biomechanical analysis. Am J Sports Med. 2009;37(8):1578–1585. doi:10.1177/0363546509332816 [CrossRef]
- Savage E, Hurren CJ, Slader S, Khan LA, Sutti A, Page RS. Bending and abrasion fatigue of common suture materials used in arthroscopic and open orthopedic surgery. J Orthop Res. 2013;31(1):132–138. doi:10.1002/jor.22185 [CrossRef]
- Edlich RF. Surgical knot tying manual. www.covidien.com/syneture. http://www.surgsoc.org.au/wp-content/uploads/2014/03/Ethicon-Knot-Tying-Manual.pdf. Accessed April 8, 2017.
- Barber FA, Herbert MA, Beavis RC. Cyclic load and failure behavior of arthroscopic knots and high strength sutures. Arthroscopy. 2009;25(2):192–199. doi:10.1016/j.arthro.2008.09.010 [CrossRef]
- Najibi S, Banglmeier R, Matta J, Tannast M. Material properties of common suture materials in orthopaedic surgery. Iowa Orthop J. 2010;30:84–88.
- DeLee JC, Drez D Jr, Miller MD. DeLee & Drez's Orthopaedic Sports Medicine: Principles and Practice. 3rd ed. Philadelphia, PA: Saunders; 2010.
- Aboalata M, Elazab A, Halawa A, Imhoff AB, Bassiouny Y. Internal suture augmentation technique to protect the anterior cruciate ligament reconstruction graft. Arthrosc Tech. 2017;6(5):e1633–e1638. doi:10.1016/j.eats.2017.06.020 [CrossRef]
- Braunstein V, Ockert B, Windolf M, et al. Increasing pullout strength of suture anchors in osteoporotic bone using augmentation: a cadaver study. Clin Biomech (Bristol, Avon). 2015;30(3):243–247. doi:10.1016/j.clinbiomech.2015.02.002 [CrossRef]
- Er MS, Altinel L, Eroglu M, Verim O, Demir T, Atmaca H. Suture anchor fixation strength with or without augmentation in osteopenic and severely osteoporotic bones in rotator cuff repair: a biomechanical study on polyurethane foam model. J Orthop Surg Res. 2014;9:48. doi:10.1186/1749-799X-9-48 [CrossRef]
- Sileo MJ, Lee SJ, Kremenic IJ, et al. Bio-mechanical comparison of a knotless suture anchor with standard suture anchor in the repair of type II SLAP tears. Arthroscopy. 2009;25(4):348–354. doi:10.1016/j.arthro.2008.10.019 [CrossRef]
- Wust DM, Meyer DC, Favre P, Gerber C. Mechanical and handling properties of braided polyblend polyethylene sutures in comparison to braided polyester and monofilament polydioxanone sutures. Arthroscopy. 2006;22(11):1146–1153. doi:10.1016/j.arthro.2006.06.013 [CrossRef]
- Barber FA, Herbert MA. Cyclic loading bio-mechanical analysis of the pullout strengths of rotator cuff and glenoid anchors: 2013 update. Arthroscopy. 2013;29(5):832–844. doi:10.1016/j.arthro.2013.01.028 [CrossRef]
- Ilahi OA, Younas SA, Ho DM, Noble PC. Security of knots tied with Ethibond, Fiberwire, Orthocord, or Ultrabraid. Am J Sports Med. 2008;36(12):2407–2414. doi:10.1177/0363546508323745 [CrossRef]
- Lo IK, Burkhart SS, Chan KC, Athanasiou K. Arthroscopic knots: determining the optimal balance of loop security and knot security. Arthroscopy. 2004;20(5):489–502. doi:10.1016/j.arthro.2004.03.005 [CrossRef]
Load to Failure Results
|Suture/Tying Technique||No. of Sutures||Load to Failure, N|
|FiberWire No. 2a|
| Safety clamp||20||78.79±1.97|
| Safety clamp||20||34.43±2.46|
Location of Break Results
|Suture/Tying Technique||No. of Sutures||Breakage Distance From Suture Knot, cm|
|FiberWire No. 2a|
| Safety clamp||20||10.45±0.34|
| Safety clamp||20||10.47±0.22|