Background: The security of several popular arthroscopic knots to prolonged, incremental, cyclic loads is unknown, as is the security of knots tied with newer, superstrong sutures.
Hypothesis: Some arthroscopic knots are as secure as openly tied square knots, and knots tied with superstrong sutures are more secure than those tied with braided polyester. Some arthroscopic knots are significantly bulkier than openly tied square knots.
Study Design: Controlled laboratory study.
Methods: Five types of openly tied knots (3-throw square, 4-throw square, 5-throw square, 5-throw slip, open SAK [simple arthroscopic knot]), 6 complex arthroscopic knots backed with 3 reversed half-hitches with alternating posts (RHAPs) (SMC, Weston, taut-line hitch, Tennessee slider, Roeder, Duncan loop), and 2 stacked half-hitch (SHH) arthroscopic knots (surgeon’s [S=S=S//xS//xS//xS], SAK [S=S//xSxS//xS]) were tied using No. 2 Ethibond around 2 aluminum rods, which were pulled apart with stepwise, incremental, cyclic loads to a maximum force of 120 N (2250 total cycles). Then, 5-throw square knots openly tied with No. 2 Fiberwire, Orthocord, or Ultrabraid were subjected to the stepwise, incremental, cyclic loading protocol extended to a 260-N load level. Before mechanical testing, the height (maximum diameter) of each knot was measured with digital calipers.
Results: For Ethibond, the openly tied 3-throw square knots (56.2 ± 21.4 N) and 5-throw slip knots (49.9 ± 26.9 N) reached clinical failure (3 mm of laxity) at significantly lower loads (P < .05) than openly tied 5-throw square knots (90.8 ± 6.5 N), whereas the openly tied SAK (82.3 ± 9.4 N) and 4-throw square (84.3 ± 11.6 N) and all arthroscopically tied knots reached 3 mm of laxity at statistically similar loads. Five-throw square knots openly tied with Fiberwire or Orthocord reached 3 mm of laxity at much higher loads (194.9 ± 28.4 N and 168.4 ± 8.6 N, respectively) than those tied using Ethibond (P < .001 for each comparison), but there was no significant difference in performance between Fiberwire knots and Orthocord knots. Although Ultrabraid square knots also were stronger than those tied with Ethibond (137.9 ± 15.9 N, P < .005), they were not as secure as those tied with Orthocord or Fiberwire (P < .05). Compared with the 5-throw square knots, all arthroscopic knots were significantly bulkier. Especially bulky knots were the Duncan loop and the taut-line hitch. Orthocord square knots demonstrated bulkiness similar to Ethibond square knots, whereas Fiberwire and Ultrabraid square knots were significantly bulkier.
Conclusions: For braided suture, 5-throw knots optimize square knot security. Open or arthroscopic slip knots can achieve similar security with post switching and loop reversal. Fiberwire, Orthocord, or Ultrabraid openly tied square knots offer greater security than those tied with Ethibond. Arthroscopic knots vary in their bulkiness, but all are significantly bulkier than 5-throw openly tied square knots. Square knots openly tied with Fiberwire or Ultrabraid tend to be bulkier than if tied with Ethibond or Orthocord, which are similar to each other.
Clinical Relevance: The 5-throw openly tied square knot remains the gold standard, although the openly tied SAK offers similar security when tying in a hole. Arthroscopic knots, whether complex knots backed up by 3 RHAPs, the 6-throw surgeon’s knot, or the 5-throw SAK, give security similar to the standard. Square knots tied with the newer sutures in open fashion are more secure than if tied with braided polyester. Using lower profile knots may be especially important when employing Fiberwire or Ultrabraid, as these sutures tend to result in bulkier knots than those tied with Ethibond or Orthocord.