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.