Biomechanical Analysis of Ligatures and Technique for Managing Drainage Tubes in Pediatric Glaucoma

Absorbable ligatures are often used with glaucoma drainage tubes to avoid early postoperative hypotony. We sought to measure the force required to ligate a drainage tube, and develop a modified technique to promote earlier release in pediatric patients, where plate encapsulation occurs more quickly than adults.

A precision digital force gauge was used to measure the tensile strength of several common ophthalmic sutures, and the necessary tensile force required to achieve tube ligation. A novel technique for tube ligation was devised to allow sutures as small as 10-0 to be effectively used.

The mean tensile strengths of unknotted sutures varied from 55.50±8.50 g for 10-0 vicryl to 477±69 g for 6-0 chromic gut. The mean tensile force required to ligate a Baerveldt or Ahmed tube was 35.9±0.9 g. However, 9-0 or 10-0 vicryl could not be reliably used for ligation, because of breakage, unless a modified technique was used, wherein the tube was first stretched to reduce its thickness and diameter.

Frictional forces inherent to knot tying make it unfeasible to reliably use 9-0 or 10-0 vicryl to ligate a drainage tube, despite the unknotted threads possessing apparently sufficient tensile strength. Our modified ligation technique overcomes this issue, allowing a wider range of suture choices, and the potential for achieving more rapid release in pediatric cases.