One-hand square knot

​​By Mathias Mejdahl, MD, PhD and Stephan Bach-Frommer, MD

​

The efficient tying of surgical knots is a critical skill for every surgeon. It is crucial the knots are tightened correctly and remain tight without causing tissue tearing and strangulation.

 

This type of suture is typically preferred if one end has a needle attached. Pull the suture through, keeping the needle end long, and the free suture end short. If the short end is pointing away from you, use the index finger throw. If the short end points away from you, use the middle finger throw. If the short end is at your right side, use either the index finger throw by the left hand or the middle finger throw by the right hand. If the short end is at your left side, use either the middle finger throw by the left hand or the index finger throw by the right hand.

 

“Middle finger throw”

• Grab the free suture end between the left thumb and index finger. 

• You now have a long suture end fixated to your instrument and a short free suture end.

• Supinate the left hand so the suture is placed on the palmar side of the fingers. The long suture end should now be placed from the opposite side so it crosses the short suture end. 

• Flex the left middle finger, catching the short suture, and pull it through the loop. Notice how you change between holding the short suture end between the middle finger and thumb, then the ring and middle fingers, and the middle finger and thumb again. 

• You can now press down on the knot with your index finger to tighten the knot.

 

“Index finger throw”

• Hold the short suture end between your thumb and middle finger.

• In a pronating movement, place the short suture end on the radial side of the index finger. 

• Place the long suture on the other side, crossing the short suture end. At the same time, catch the short suture end with the index finger and pull it through the loop.

• Let go of the suture end with your thumb and middle finger and instead catch it between the index and middle fingers to pass it through the loop. 

• Hold the short suture end with your thumb and middle finger again and press down on the knot with your index finger to tighten the knot.