Assessment of four tissue models on knot tensile strength.

OBJECTIVE To determine whether the tissue model onto which a knot is tied influences the knot's tensile strength. STUDY DESIGN Zero-gauge, nonexpired, silk, polyglactin 910, polydioxanone, and polypropylene sutures were tied on 4 different mock tissue models. The tissue models were standard metal hex head screw, uncooked chicken breast, a tube of packaged "string" cheese, and a cylinder of bubble wrap. The knots were tied without a surgeon's knot and with 4 additional square knots (1 = 1 = 1 = 1 = 1). The knots were tied by a single obstetrician/gynecologist investigator (J.M.D.) over the period of 1 week to minimize fatigue. We compared the knots when subjected to a tensiometer until the suture broke or untied. A minimum of 20 knots per group were needed to detect a moderate effect size with a power of 85% and a type I error rate of 5%. RESULTS A total of 407 knots were tied with 4 types of material (silk, polyglactin 910, polydioxanone, and polypropylene), using 4 different models (chicken, bubble wrap, cheese, and metal). Among the knot failures, 113 of 407 untied rather than broke (28%). No differences in the likelihood of knots coming untied between the different models (p = 0.34) or tension at failure (p = 0.81) were noted. A 4 × 4 factorial analysis of variance (ANOVA) was conducted to determine the effects of the suture material and model type on tension at failure and whether there was any interaction between the 2 factors. No significant difference was observed in the interaction between suture material and model type (p = 0.35), and no effect for model type was found (p = 0.22). CONCLUSIONS Tissue models that use materials more similar to human tissue do not seem to influence knot strength when compared with standard metal models. We propose that it is possible to have an accurate understanding of how knots withstand force and to simulate an in vivo environment by using low-cost, easily accessible natural and synthetic materials for the mechanism onto which the knot is tied.