Knot security in simple sliding knots and its relationship to rotator cuff repair: how secure must the knot be?

We sought to determine which simple sliding knot configurations would have adequate strength for rotator cuff repair. Four knot configurations were tied with both No. 1 polydioxanone suture and No. 2 Ethibond suture (Ethicon, Somerville, NJ) using 3 different tying techniques: hand-tie, standard knot pusher, and cannulated double-diameter knot pusher. The knots were then tested to failure on a materials testing system. The weakest standard knot configuration was S=S=S=S. The other 3 knot configurations (S//S//S//S, SxSxSxS, and S//xS//xS//xS) generally failed in the 35 to 50 N range. Ultimate strength in this range can be shown to be adequate to withstand, without suture failure, a maximal contraction of a repaired rotator cuff tear within the rotator crescent, assuming certain conditions are met (suture anchors placed 1 cm apart, 2 sutures per anchor). More complex knots are not necessary for adequate knot security. However, the same configuration with only 1 suture per anchor will not be strong enough because the suture will fail under maximum physiological load. This study shows that we can predict the adequacy of a given knot configuration under maximum physiological loading conditions.