Poor knot security when closing running sutures with three threads

Knot security varies with half-knot and half-hitch sequences, rotation sense, and the type and diameter of sutures.

To evaluate the security of knots with three threads, as used for tying off running sutures.

Three-way randomised experiments, with a factorial design and 10 knots/cell. The first experiment evaluated the knot security of a surgical knot (H2H1sH1s) for single stitches (2 threads) or running sutures (3 threads), using polyglactin 910 or polydioxanone, of 2-0 or 1 diameter. The second experiment evaluated the knot security of a running suture with 4 or 5 half-hitch sequences and 2 or 3 blocking knots, using polyglactin 910 or polydioxanone, and with diameters of 2-0 or 1.

Knot security in Newton, measured with a digital dynamometer. With increasing forces, the knot either slipped open or blocked, causing the suture to break.

In the first experiment, the knot security of surgical knots was less with monofilament (P=0.0004) and running sutures (P<0.0001), but not with suture diameter (three-way analysis of variance). Variability in outcome was greater with running sutures, especially with monofilament sutures of larger diameter. The second experiment demonstrated that half-hitch sequences occasionally opened with low forces, especially with larger monofilament sutures.

Compared to knots tied with two threads, knots with three threads have a lower and more variable knot security, especially with larger monofilament sutures.

Knots with 3 threads should be avoided, as they may occasionally open with forces below 30 or 10 Newton.