Mechanical Performance of Knots Using Braided and Monofilament Absorbable Sutures
Drs. Daniel C. Schubert, James B. Unger, Debi Mukherjee, Jack F. Perrone
Louisiana State University Health Sciences Center
Shreveport, Louisiana

Objective:   To test the integrity various flat and sliding knots with braided and monofilament absorbable sutures.
Materials and Methods: There were four study groups, each of which consisted of a single suture type and size with 5 different knots.  Each combination was tested 10 times for a total of 200 experiments. The suture types used were 0 and 2-0 monofilament Glycomer 631 (Biosyn®) and 0 and 2-0 coated braided Lactomer (Polysorb®).  The flat knots tested were the square (1=1=1=1=1=1), surgeon’s (2=1=1=1=1), and modified granny knots (1x1=1=1=1=1). The sliding knots (S) were the modified identical (S=SxSxSxSxS) and  non-identical knots (SxSxSxSxSxS). A tensiometer was used to stress the loops of the knots until knot failure occurred.  Failure was defined as untying of the knot or breakage at the knot. We compared the proportion of knots becoming untied within each of the 4 suture groups as well as the ultimate load required to break the remaining tied knots.   
Results: All knots that untied did so between 14N and 68N of load. In the 0 lactomer suture group 90% of the modified identical sliding knots became untied compared to 10% of the non-identical sliding knots, 0% each of the flat square knots and flat surgeon’s knots, and 10% of modified granny knots, x²(4)=34.3,p<.0001. In the 2-0 lactomer suture group 60% of the identical sliding knots became untied compared to 10% of the non-identical sliding knots and 0% each of the 3 flat knots, x²(4)=22.6,  p=.0002. In the 0 glycomer 631 group 40% of the non-identical sliding knots became untied compared to 20% of the modified identical sliding knots, 10% of the modified granny knots, and 0% each of the square and surgeon’s knots, x²(4)=9.3, p=.05. In the 2-0 glycomer 631 group there was no significant difference between the proportion of knots becoming untied (20% square knot, 30% modified granny knot, 0% surgeon’s knot, 0% modified identical sliding knot, 10% non-identical sliding knot, x²(4)=6.4, p=.17). Ultimate load required to break knots that remained tied ranged from 130.1 N to 141.6N in the 0 glycomer 631 group, 136.7N to 147.0N in the 0 lactomer group, 88.0N to 99.1N in the 2-0 glycomer 631 group, and 107.4N to 114.7N in the 2-0 lactomer group. Only in the 0 lactomer group was there a significant difference between the loads required to break various knots, F=3.49, v _n=4, v _d= 45, p =.02.
Conclusions:   When using 0 and 2-0 lactomer suture modified identical sliding knots should be avoided. When using 0 glycomer 631 non-identical sliding knots may not be as secure as other knots and perhaps should be avoided as well.
Key Words: Flat knots, sliding knots, braided suture, monofilament suture