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

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

METHODS: 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.

RESULTS: 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).

CONCLUSIONS: 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.