Slipping the knot: a comparison of knots used in adjustable suture strabismus surgery

PURPOSE To evaluate the frictional force created by different knots used in adjustable suture strabismus surgery. METHODS To allow the simulation of strabismus surgery suture tying methods a model using 6-0 polyglactin 910 suture was created. Three different knots were evaluated: (1) the sliding noose knot with a double wrap of suture, (2) the cinch knot with a single throw on both sides of the pole suture, (2) and a single-throw square knot. (Bow-tie knots were not included.) A digital force meter was used to measure the force (gram-force [gf]) required to overcome the static friction created by the knot. Each simulation was repeated with new suture material 5 times and the force required after subsequent repositioning was also recorded. RESULTS The force to overcome static friction of the sliding noose knot was 240 gf [95% CI, 187-284 gf]; of the cinch knot, 150 gf [95% CI, 123-167 gf]; and of the square knot, 110 gf [95% CI, 95-121 gf]. Subsequent movement of each knot along the same suture required progressively less force, with the sliding noose maintaining the most static friction. CONCLUSIONS The sliding noose knot generates the most frictional force and also maintains the most friction after subsequent repositioning. Important consideration should be given to multiple repositioning movements, because the force required for each subsequent repositioning decreases.