Recent advances in anterior segment surgery have increased the attention given to control of astigmatism following placement of sutures in a corneal or limbal wound. Several knots have been proposed to allow the surgeon to control the tension on such knots intraoperatively.1,2 Because the techniques in tying these knots are relatively complex and the knots themselves are large and difficult to bury in the corneal stroma, we developed an adjustable knot which is easier to tie and easier to bury. This knot is a series of three overhand knots with a granny relationship between the first and second throws and a square relationship between the second and third throws (Fig 1).
Figures 1 to 11 demonstrate the technique from the surgeon's perspective.
All the previously proposed slip knots work well in terms of the surgeon's control of suture tension. After several thousand uses over the past 3 years, we have found that our knot allows similar control over suture tension and astigmatism, but has the additional advantages of ease of tying and smaller knot size. In corneal transplants, in particular, suture burial as well as later selective suture removal are facilitated by this small knot. On only one occasion have we noted one of these knots to untie spontaneously. In practice, it has not been necessary for the third overhand knot to bear a square relationship to the second overhand knot, since the third knot tends to bind well even if it bears a granny relationship to the second knot.
This technique has another advantage: it can be used when the suture ends are very short, because the first throw involves only one loop instead of the commonly used three loops.
Our knot is adjustable because of the poor binding of the granny knot as opposed to the square knot. The knot described by Dangel and Keates relies on the orientation of the suture at the time the knot is pulled down to prevent premature binding. The knot described by Terry is a true slip knot in which a binding throw is deferred until the proper tension is attained. Our knot is the mirror image of one of the knots described by Dangel and Keates but it is tightened in a different direction.
We have encountered two minor problems with our knot. First, sutures smaller than 10-0 nylon (ie, less than 22 µ in diameter) are not suitable for use with this knot because the knot tends to bind too quickly and does not allow the suture to be adequately tightened in a large percentage of cases. Therefore, we use it only for 9-0 nylon and 10-0 nylon closures. Second, if the suture is allowed to become dry or form kinks during adjustment of suture tension, the knot may bind prematurely and necessitate replacement of the suture. Overall, we have not found this last problem to be significant when reasonable attention is paid to the handling of fine nylon suture.
FIGURE 1: (A) A square knot.
(B) A granny knot.
(C) A granny knot locked by a square knot.
FIGURE 2: The proximal end of the suture is grasped with tying forceps held in the left hand. Tying forceps held by the right hand are placed to the left of the point where the suture emerges from the tissue.
FIGURE 3: The suture is wrapped around the forceps held by the right hand and these forceps are used to grasp the distal end of the suture.
FIGURE 4: The first overhand throw is completed.
FIGURE 5: The tying forceps held in the right hand are placed on the right side for the suture held by the forceps held in the left hand.
FIGURE 6: The suture is wrapped around the suture held by the right hand and these forceps are used to grasp the distal end of the suture.
FIGURE 7: The second throw of the knot is completed, thus creating a granny knot.
FIGURE 8: The suture is pulled to the right and the left until appropriate tension has been achieved.
FIGURE 9: The forceps held by the right hand are placed on the right side of the suture held by the forceps in the left hand.
FIGURE 10: The suture is wrapped around the sutures held in the right hand and these forceps are used to grasp the distal end of the suture.
FIGURE 11: The knot is tightened.
1. Terry C. The differentially adjustable slideknot. American Intraocular Implant Society Journal. 1977;3:197.
2. Dangel ME, Keates RH. The adjustable slideknot - an alternate technique. Ophthalmic Surg. 1980;12:843.