Tie hard 2- an in-vitro comparison of first throw tension holding in twisted v straight-first throws; using Polyglycolic acid (Dexon S), Polyglactin 910 (Coated Vicryl).

Objective: To compare the first throw tension holding properties of twisted versus straight first throws in two commonly used Oculoplastic braided absorbable sutures.

Design: An in-vitro experimental model.

Methods: Variable loads were applied to the first double throw of a surgical knot - either in straight-line configuration or twisting the knot using both 6/0 Polyglycolic acid (Dexon S) and 6/0 Polyglactin 910 (Coated Vicryl). Each suture was tested to the point of knot slipping and the critical tension recorded. Two variations of the experiment were undertaken: Experiment 1 - two metal loops were brought together by the test suture, experiment 2 - two strips of tissue (Permacol - cross-linked porcine dermal collagen) were brought together by the test suture.

Results: Experiment 1 straight: Polyglycolic acid 12.2g (11-13.5), Polyglactin-910 2.5 g (2.5- no range). Experiment 1 twisted: Polyglycolic acid 13.33 g (10-15), Polyglactin 910 3 g (2-5). Experiment 2 straight: Polyglycolic acid 33g (30-35), Polyglactin 910 25g (25 - no range). Experiment 2 twisted: Polyglycolic acid 35 (30-40), Polyglactin 910 25g (20-30).

Conclusions: Twisting the suture adds only a modest increase in first throw knot security. Polyglycolic acid (Dexon S) braided absorbable suture has significantly better first throw knot security when compared with Polyglactin-910 (coated Vicryl). This is an important property when suturing tissues under tension as it minimises slippage before the locking throw is tied.