Influence of testing conditions on primary stability of arthroscopic knot tying for rotator cuff repair: slippery when wet?

PURPOSE: The purpose was to evaluate whether the knot security of sliding and nonsliding knots with different sutures is influenced by dry or wet conditions.

METHODS: We tested 5 suture materials, all of them US Pharmacopeia No. 2: PDS (polydioxanone) II (Ethicon, Somerville, NJ), Ethibond (Ethicon), and 3 ultrahigh-molecular weight polyethylene (UHMWPE) sutures-FiberWire (Arthrex, Naples, FL), Orthocord (DePuy Mitek, Raynham, MA), and Herculine (Linvatec, Largo, FL). Testing was performed under dry and wet conditions with sutures soaked in a saline solution. Cyclic loading was performed to simulate physiologic conditions. We started with a tensile load of 25 N. After 100 cycles, the load was increased to 50 N for another 100 cycles. The tensile load was gradually increased by 25 N per 100 cycles until suture rupture or knot slippage, defined as lengthening over 3 mm.

RESULTS: Under dry conditions, 170 suture ruptures and 30 knot slippages were reported; and under wet testing conditions, 186 suture ruptures and 14 knot slippages were reported, with P < .044 and P < .027, respectively. Failure by knot slippage (n = 44) was seen under dry and saline solution conditions mainly with UHMWPE sutures, in particular with the Herculine suture using a Roeder knot showing comparable maximum failure loads in dry (274.5 ± 58.2 N) and saline solution (312.5 ± 14.2 N) conditions (P > .056). Knot slippage occurred only with sliding knots. With the Ethibond suture, no knot slippage was found regardless of the testing conditions and knot type. Across all knot types, the UHMWPE sutures were significantly stronger with respect to clinical and maximum failure loads in ultimate load to failure than Ethibond and PDS II under dry and wet testing conditions (P < .001 for both).

CONCLUSIONS: We conclude that testing of different suture materials and knot types is different in wet versus dry conditions and believe that biomechanical testing might be more realistic in a wet environment.

CLINICAL RELEVANCE: Suture knots behave differently in a wet versus dry environment, and testing of knot mechanics might better be carried out in wet environments.