Penetrating keratoplasty (PK) still remains the predominant procedure in corneal graft surgery. Complications include wound dehiscence, immune-mediated rejection, and refractive errors.1 A study by Jeganathan et al2 showed that resuturing of corneal wounds after PK may be required for various reasons, including wound dehiscence, loose sutures, and infectious keratitis, which can increase the incidence and severity of complications many fold.2, 3 There is evidence that inflammatory response and adhesion formation surrounding the sutures are most pronounced at the site of the knot.4, 5

Three different knots, 3/1/1, 1/1/1(slip-knot), and 1/1/1/1(modified slip-knot), were compared using 10-0 black monofilament polyamide-6 suture (Ethilon 30 cm with a 6-mm micro-point spatula needle, Johnson & Johnson, New Brunswick, NJ, USA). A special apparatus was designed for the study (Figure 1). The horizontal and vertical sizes of the knots and slippage were measured with a calibrated eyepiece graticule using a Nikon-E51i binocular bright-field microscope (New York, NY, USA). Knot slippage was observed at 5 and 24 h. The study was repeated five times for each knot type. Knot morphology was observed using a scanning electron microscope (Figure 2).

Figure 1
figure 1

Schematic diagram of the knot under study.

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Figure 2
figure 2

(a) (Left): Scanning electron microscope image of 3/1/1 knot (100 μm); (b) (middle): scanning electron microscope of knot 1/1/1/1 (100 μm); (c) (right): scanning electron microscope image of 1/1/1 (100 μm).

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Using a tension weight of 10 g, the mean slippage of knots measured at 5 and 24 h was least with 3/1/1 and maximum with 1/1/1 (Figure 3a). Using a tension weight of 20 g the mean slippage of knots at 5 h was least with 3/1/1 and maximum with 1/1/1/1, while at 24 h it was equal with 1/1/1 and 1/1/1/1 (Figure 3b). The knot size was measured in vertical and horizontal axes to the suture line. The 3/1/1 knot was found to be the largest (Figure 3c). There was no significant difference seen in the size of 1/1/1 and 1/1/1/1 knot.

Figure 3
figure 3

(a) Knot slippage with 10-g weight (top left: mean slippage at 5 h; top right: mean slippage at 24 h). (b) Knot slippage with 20-g weight (middle left: mean slippage at 5 h; middle right: mean slippage at 24 h). (c) Average knot morphology of the three different types of knots (bottom left: horizontal knot size; bottom right: vertical knot size). (Error bars show ±95% confidence interval (CI))

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Paired t test was used for statistical analysis (Data analysis toolpak, SPSS, Chicago, CA, USA) (Table 1).

Table 1 Statistical values of paired t tests used to compare knots
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In conclusion, our study demonstrates that 3/1/1 is the most secure knot with least slippage but was the largest of the three knots. The 1/1/1 knot showed the most slippage. The 1/1/1/1 knot may be a better knot type with benefits of minimum slippage and a smaller knot size, making it easy to bury.