INFLUENCE OF TESTING CONDITIONS ON PRIMARY STABILITY OF ARTHROSCOPIC KNOT TYING FOR ROTATOR CUFF REPAIR: SLIPPERY WHEN WET?

Abstract

In recent years UHMWP sutures have gained more and more popularity in shoulder surgery. They have an increased tensile strength but were shown to have a higher rate of knot slippage due to their smooth surface. There exist different testing protocols on suture testing in dry or in wet conditions.

The purpose of this study was to gain some inside as to whether or not the knot security of sliding and non-sliding knots with different suture materials is influenced by dry or wet testing conditions.

We tested five common suture materials, all of them USP #2. The PDSII, the Ethibond and three ultra high molecular weight polyethylene (UHMWPE) sutures: Fiber Wire, Orthocord and Herculine. As non-sliding knots we used Square knot and Revo knot and for sliding knots we used Fisherman and Roeder knot. 10 samples of each knot type were tested. In the first group knot tying and biomechanical testing were performed under dry conditions. In the second group the sutures were soaked in saline solution for 3 min. before knot tying and afterwards tested in saline bath. Cyclic loading was performed to simulate the physiological conditions. We started with a tensile load of 25 N. After 100 cycles, the load was increased to 50 N for another 100 cycles. Until suture rupture or knot slippage of 3 mm the tensile load was gradually increased by 25 N per 100 cycles. Under dry conditions 170 suture ruptures and 30 knot slippages were recorded. Under wet testing conditions 186 suture ruptures and 14 knot slippages were seen, which tested statistically significant. Failure by knot slippage (n=44) was seen under dry and saline testing conditions mainly with UHMWPE sutures particularly with Herculine suture. Knot slippage occured only with sliding knots. With the Ethibond suture no knot slippage was found regardless of the testing conditions and applied knot type. Across all knot types the UHMPE-sutures were significantly stronger in ultimate load to failure than Ethibond and PDSII under dry and wet testing conditions.

Is the information we get from testing dry suture material reliable and helpful for our daily practice? Our study clearly showed: No! The mode of failure and the number of knot-failure differs significantly in wet testing conditions compared to dry testing. We found that the number of knot-failures is higher when tested with dry sutures than in wet testing conditions. The soaking of the suture material with fluid improves its “skid-resistance”. As we expected showed the UHMWP sutures with their smooth surface a high number of knot-failures compared to polyethylen suture Ethibond, which did not show a single knot-failure in dry or wet tesing conditions. The maximum failure load showed clearly the superiority of the new UHMWP suture material, with around 300 N being double as high as for polyethylen and polydioxone sutures.