Strength of knots in surgery in relation to type of knot, type of suture material and dimension of suture thread.

The 12 commonest types of suture material in dimensions 7/0, 5/0, 000, 0 and 2 (USP, 1965) were tested in 16 types of knot with regard to tensile strength of knot using the loop method. The results are given in tabular form as the strength of the loop for alltypes of knot tested, and as the mean knoe efficiency for certain groups of knots. The knot efficiencies are compared with regard to the different types of knot, the various types of suture material, and the different dimensions of thread using statistical methods including variance analysis. The strength of unknotted thread within a given dimension showed considerable variations for different suture materials: a given material could be more than twice as strong as the weakest material of the same dimension. With very few exceptions, the knot was the weakest point in a suture loop subjected to disrupting forces. The knot efficiency depended very largely on the type of knot and the strength of different types of knots varied from 3% to 99% of the corresponding unknotted thread. With the exception of two types of steel thread and both types of catgut, the efficiency was low for most simple crossed knots and for many simple parallel knots, and here considerable variations were recorded. Knot efficiency was clearly highest and showed least fluctuation with complex and particularly complex knots, and was closely similar for these. The dependency of knot efficiency on the type of suture material (mean for 16 knots) varied from 44% (polyethylene) to 90% (multifil steel). The variations in dependency on material were greatest with simple knots and with certain materials, and decreased with increasing knot complexity. The dependency of knot efficiency on the dimension of any particular suture material was apparently of much less importance than the type of knot and type of material.