Purpose: The study in vitro compares primary fixation strength of two arthroscopic flip knots; clinical knot security and ultimate load to failure. SMC knot is well known and frequently used arthroscopic knot. SAK (Secure Arthroscopic Knot) is fully instrumental knot, easy to master, with short learning curve. Published 10 years ago, during that period it is predominantly used by senior author in arthroscopic shoulder procedures.

Materials and Methods: Curved metal rods are put in grips of the Universal Testing Machine and positioned centraly in vertical orientation 5 mm apart. The curvature of each rod was wrapped with 2 mm deerskin soaked in saline. Arthorscopic canulla was positioned in holder on the same position during testing procedure for all knots. Knots – 8 SAK and 8 SMC – were constructed outside the canulla, slided and positioned with arthroscopic knot pusher on the concave side of the caudal rod. Four additional loops (left-right alternatively) were put on the knot. Orthocord was used in all procedures, and all knots were performed by the same surgeon. The construct was preloaded with 7 N and distracted 0, 1mm/s. Ultimate tensile load (UF) and clinical load to failure (CF) were determined. Clinical load to failure is defined as force that distract knot for 3 mm. Data distribution was analysed and parametric statistics was performed.

Results: Clinical failure for SAK is 249±29 N, and for SMC 191±40 N, and this difference is significant on the level of 5 %. Ultimate failure of SAK is 292±34 N and for SMC 276±39 N, and this difference is not significant. SAK failured with breakage in 7 out of 8 measurments, and SMC failured equaly by slipage and breakage.

Discussion/Conclusion: The study imitated in vivo condition, slipage of knots during test was eliminated using deerskin which simulated human tissue. Both knots are equally strong regarding ultimate load to failure in hands of the experienced shoulder arthroscopist. Secure arthroscopic knot (SAK) presented greater load to clinical failure comparing with SMC knot. Autors can recomend SAK as an easy and safe arthroscopic flip knot.