The force required to advance the knot is called knot rundown force. Once meticulous approximation of the wound edges is achieved, the surgeon prefers to add one more throw to the two-throw knot so that it does not fail by slippage. The magnitude of the knot rundown force is influenced considerably by the configuration of two-throw knots. Failure of the knotted suture loop may be the result of either knot slippage or breakage, suture cutting through tissue, and mechanical crushing of the suture by surgical instruments. Initially, the knotted suture fails by slippage, which results in untying of the knot.
All knots slip to some degree, regardless of the type of suture material.
3 Dermal sutures are, however, an exception to this rule. The degree to which a knot slips can be influenced by a variety of factors including the coefficient of friction of the suture material, suture diameter, moisture, knot type, and final geometry.