Knot integrity as a function of suture expiration.

OBJECTIVE To test the integrity of knots tied with expired suture and non-expired suture, using 5 different suture materials. STUDY DESIGN Knots were tied using expired and non-expired chromic catgut, polyglactin 910, polydioxanone, silk, or coated polyester. Expired sutures were a mean of 10.5 years past the date of expiration stamped on the packaging. Suture packaging was inspected for any flaws or humidity. There were 116 knots with expired suture and 109 non-expired knots. All knots were tied by hand. Suture was soaked in 0.9% sodium chloride for 60 seconds and subsequently transferred to a tensiometer where the tails of the knots were cut to 3 mm length. We compared the tensile strength of knots using a tensiometer to pull the knots until the suture broke or untied. A minimum of 30 knots were needed in order to detect a statistically significant main effect for expired and non-expired sutures with 80% power and a 5% chance of type I error. RESULTS A total of 225 knots were tied. Overall, we found no difference in mean tension between expired suture (77.5 ± 31.7 N) and non-expired suture at failure (81.9 ± 30.2 N). All the sutures broke at the knot and none untied. Expired chromic and polydioxanone were significantly weaker than the non-expired suture of the same material (p = 0.002 and p = 0.001, respectively). There was no statistically significant difference in tensile strength between expired absorbable or permanent suture materials. Based on a univariate analysis of variance ([SCAP]ANOVA)[R] there was no difference in the tension at failure between expired and non-expired sutures with suture packet as a covariate. No suture untied when knotted with expired suture. CONCLUSIONS Under laboratory conditions, expired chromic and polydioxanone sutures broke at lower tensile strength than non-expired sutures of the same material.