Securing extraocular muscles in strabismus surgery: laboratory analysis of biomechanical parameters related to the...

To investigate the tensile properties of several components used to secure extraocular muscle to sclera in strabismus surgery to determine potential failure points.

A digital force gauge measured the tensile strength of intact or damaged 6-0 Vicryl suture (Ethicon, Somerville, NJ), as well as threads tied in a 2-1-1 or 2-1-1-1 surgeon's knot configuration. Human sclera was used to test the resistance to drag of knotted and unknotted 6-0 Vicryl suture thread through partial thickness sclera. Mean values were compared using a t test.

The mean tensile strength of 6-0 Vicryl suture was 623.5 g, but it was markedly reduced by damage from the needle (P < 0.0001) or ophthalmic needle holder (P < 0.0001). The 2-1-1 knots broke at a mean force of 307.6 g, compared with 292.8 g for 2-1-1-1 knots (P = 0.84). Drag through a 2 mm scleral tunnel was 4.6 g, compared to 13.6 g for a 4 mm tunnel (P = 0.011). The force required to pull a knotted suture through a 4 mm scleral tunnel was 254 g for a 2-1-1 knot and 367 g for a 2-1-1-1 knot (P < 0.015).

Although 6-0 Vicryl possesses adequate tensile strength for muscle fixation, thread damage from a needle or needle holder may cause serious losses in tensile strength. Knot-breaking strength is not significantly increased by adding a fourth throw. Frictional forces of the scleral tunnel are not sufficient to provide muscle stabilization, but the presence of a knot can provide substantial resistance to suture slip into the scleral tunnel.