Instrument Tie – Square Knot
Wayne W. LaMorte, M.D., Ph.D., M.P.H.
Photography by Michael J. LaMorte
The square knot is the most fundamental knot for the surgeon. Well-constructed square knots with flat throws have less likelihood of slipping. The instrument tie is commonly used for closure of superficial lacerations because it conserves suture material and can be done quickly.
1) This shows the beginning of knot construction.
Note that the short end is beneath the tubing, away from the surgeon.
2) The needle holder is held above the tubing pointing from right to left.
The left hand has brought the long end away from the surgeon to begin to form a loop.
3) The long strand has now been looped around the needle holder, and the tip of the needle holder is being rotated away from the surgeon to grasp the tip of the short end.
4) The needle holder, which now protrudes through the loop, grasps the short strand, and it will be pulled back through the loop toward the surgeon.
5) As the short end is pulled toward the surgeon, the long end is pushed away.
6) The throw is tightened by pulling with equal tension in both directions.
7) The left hand initiates creation of the 2nd loop by bringing the long strand toward the surgeon.
Note that the short end is now toward the surgeon, and the needle holder again is pointing to the left.
8) The left hand brings the long strand toward the surgeon across the needle holder to form a loop. The tip of the needle holder will now be rotated toward the surgeon to grasp the short end.
9) The tip of needle holder has now been rotated toward the surgeon, and grasps the short end, which will be pulled back through the loop.
10) The needle holder has now pulled the short end back through the loop away from the surgeon, and the left hand pulls the long strand toward the surgeon..
11) The second throw is tightened by pulling with equal tension in opposite directions. Additional throws are added, alternating between the first and second throws. For braided suture material, such as silk, 3 throws are generally sufficient. For monofilament material, such as nylon or prolene, 5 or 6 alternating throws are required to prevent knot failure.