The effect of an air knot on surgical knot integrity

Surgical trainees may tie air knots, which have a questionable tensile strength and rate of untying. The purpose of this study was to determine the effect of an air knot on knot integrity.

The 5 suture materials tested were 0-0 gauge coated polyethylene, polyglyconate, glycolide/lactide, polypropylene, and silk. The suture was tied between 2 hex screws 50 mm on center. The strands were tied using 5 square throws, and the knot tails were cut at 3-mm length. To create a standardized air knot, a round common nail measuring 3 mm in diameter was inserted between throws before tying square throw #3. The suture loop was positioned around the upper and lower hooks of the tensiometer so the location of the knot was roughly equidistant from the hooks. Ultimately, either the loop broke or the knot slipped. At that time, the peak tensile force as well as the outcome of the knot were recorded.

A total of 480 knots were tied. The presence of an air knot significantly lowered the tension at knot failure in the glycolide/lactide (P = 0.0003), polypropylene (P = 0.0005), and silk (P = 0.0001) knot configurations. Air knots had the same integrity as surgical knots when coated polyethylene and polyglyconate suture were used. Linear regression was performed and identified both suture material (P < 0.0001) and presence of an air knot (P < 0.0001) to be independently associated with a lower tension at failure.

Under laboratory conditions, an air knot may contribute to a lower tensile strength at failure for certain suture materials.