Securing Extraocular Muscles in Strabismus Surgery: How Strong Is the Sclera?

Securing extraocular muscles in strabismus surgery: effect of cautery on suture strength

An experimental study was performed to evaluate quantitatively the effect of cautery on the tensile strength of sutures commonly used in strabismus surgery. This in vitro study was conducted in a controlled fashion using 6-0 polyglactin 910 suture, two different forms of cautery, and a precision digital force gauge. The results suggest that thermal electrocautery with a wire tip can substantially weaken or break 6-0 polyglactin threads only if direct contact is made, but bipolar cautery at typical ophthalmic surgical settings does not.

Securing extraocular muscles in strabismus surgery: biomechanical analysis of muscle imbrication and knot tying technique

An experimental study was performed to quantitatively evaluate the tensile strength implications of two important steps in extraocular muscle surgery: muscle imbrication and knot configuration. The study was conducted in a controlled fashion using fresh ex vivo pig eyes with extraocular muscles attached and a precision digital force gauge. The study provides clinically translatable data to inform optimal surgical technique. The results suggest that imbrication of the muscle edge is most secure when the suture is looped around itself in a manner that allows it to be tightly cinched and locked and that granny knots possess similar tensile strength to square knots.

Securing extraocular muscles in strabismus surgery: biomechanical analysis of knot-tying technique

BACKGROUND

The safe and precise reattachment of extraocular muscles requires a technical approach that minimizes any opportunity for the muscle to slip intraoperatively or postoperatively while minimizing surgical risk. Biomechanical testing can provide important quantitative information about the tensile properties of different knot configurations that may inform surgical technique.

METHODS

A precision digital force gauge was used to assess the tensile strength created by different knot tying techniques and configurations in human sclera using 6-0 polyglactin 910 suture.

RESULTS

The mean tensile strengths of the first knot throw formed with either one, two, or three loops, with widely separated scleral tunnels, were 5 g, 10 g, or 27 g, respectively. When the scleral tunnels are closely spaced in a "cross-swords" fashion, the mean strength of a first throw made with two loops increased to 385 g. If a first throw with two conventional loops was cinched against one of the scleral tunnels or a reversed first loop is used, the mean tensile strength increased to 112 g or 381 g, respectively, even with widely spaced scleral tunnels.

CONCLUSIONS

Proper cinching or minor modification of the first knot throw provides excellent tensile strength, even with short, widely spaced scleral tunnels, comparable to that achieved with the technically more demanding crossed swords technique. Conventional, noncinched first throws are prone to slip at low force when scleral tunnels are widely separated, though the resistance increases as the number of loops increases.