Knot Security: Introduction
Introduction to Knot Security
Knot security is determined by a number of factors. Even when a knot is tied correctly using the "square" configuration, with the appropriate number of throws, knot security can still be compromised. The length of the knot ears and the characteristics of the suture are import factors affecting the security of the knot. Let us take a closer look at these factors.
Close up of knot ears
Length of Knot Ears
Generally speaking, the length of knot ear required to form a secure knot is related to the inherent "memory" or stiffness of the suture. For most synthetic sutures used in surgery today, leaving 3 mm ears on knots is recommended. If knot ears are cut more flush with the knot, an additional throw is required to maintain knot security. For chromic catgut, adding an additional 1 to 2 mm of length to the standard knot ear length (i.e., a total of 4 to 5 mm) is recommended, since catgut suture swells as it absorbs body fluid, and this might cause the last throw on the knot to untie, particularly when the ears are cut short.