MODIFIED COW-HITCH SUTURE FIXATION
Alison Fraenkel, BBiomedSc, MBBS, MScMed(OphthSc) and Lawrence Lee, MBBS, FRANZCO, FRACS
The modified cow-hitch suture fixation described here is a technique that was developed for 2-point transscleral fixation of a CZ70BD lens (Alcon Laboratories, Inc) in the ciliary sulcus when there is insufficient capsular support for in-the-bag lens positioning. Two partial-thickness triangular scleral flaps are made 180 degrees apart with a scleral tunnel in each. Two separate 10-0 polypropylene sutures are inserted blunt-end first through the scleral tunnels. A Kuglen hook is used to retrieve one suture loop per needle via a small limbal incision. The modified cow-hitch knot is created at each lens eyelet by grabbing the tip of the suture loop, feeding it up and through an eyelet, retrieving the trailing double strands through the loop to form a second loop that is double stranded, throwing this loop over the free end of the haptic, over to the optic side of the eyelet, and then pulling to secure. Widening of the limbal incision facilitates lens implantation. The modified cow-hitch suture knot is particularly secure because of the high number of loop segments in contact with each other, the lens haptic, and the eyelet. This maximizes the static friction of the knot and distributes opposing forces over multiple points on the haptic. A retrospective case series where this technique was used in 82 eyes, with an average follow-up time of 23 months, lends support to the safety and efficacy of the modified cow-hitch technique.
The modified cow-hitch suture evolved as a means of secure 2-point transscleral fixation for an intraocular lens (IOL) in the sulcus that avoids internal suture ends and minimizes intraocular manipulation. A CZ70BD lens and two 10-0 polypropylene sutures are the materials of choice. The technique evolved as a result of the ubiquity and suitability of the CZ70BD lens for ciliary sulcus placement along with consideration of the risks of single-pass suture knots and internal suture ends. These risks include lens dislocation from single-suture breakage and intraocular tissue compromise from exposed suture tips.
The modified cow-hitch suture technique has been substantiated by a retrospective case series of 82 eyes in 79 patients.1 With a mean follow-up time of 23 months, there were no cases of suture breakage. Visual outcomes were favorable, with 45 eyes (55%) achieving a best corrected visual acuity (BCVA) of 20/40 or better and 61 eyes (74%) experiencing an improvement in BCVA. The modified cow-hitch suture technique is demonstrated in Video 34-1 and elaborated on here so that readers are familiarized with this technique as an option where there is an indication for an IOL but insufficient capsular support.
History
The cow-hitch knot is defined in the The Ashley Book of Knots as “[t]he hitch by which farmers stake out their cows to nibble favoured grass in restricted places.”2 Figure 34-1 illustrates the knot in its most basic form. The knot is executed by taking a loop of string, throwing it over the object to be tied, reaching through the loop to grab its 2 composite strands, then pulling those strands back through the loop until the line is taut. This can be done with a discrete length of string folded in half or with a continuous loop of string. Although the cow-hitch knot earned its name in the pastures, it was described for use as a surgical knot by the Greek physician Heraklas in the 1st century AD by the translated name of the “threaded noose.”3 In Heraklas’s short essay titled “Sixteen Surgical Nooses and Knots,” he detailed its utility for limb traction and fracture reductions in orthopedic procedures.3 The cow-hitch knot has since been adopted on a more elegant scale for ophthalmic use, and many cow-hitch and modified cow-hitch methods of transscleral lens fixation have been described.1,4–9 We advocate that the modified cow-hitch method detailed in this chapter is particularly safe, effective, and durable.
Figure 34-1. The basic form of a cow-hitch knot. By definition, the cow-hitch knot is tied by taking a loop of line, throwing it over an object, reaching back through the loop to grab the lagging double strand, and pulling the double strand through the loop to secure the object.
Indications
Indications for our modified cow-hitch suture include lack of capsular support in cases of aphakia or lens dislocation. Specifically, we have described the technique in eyes that have experienced complex retinal detachment surgery, intracapsular cataract extraction, complicated cataract surgery, traumatic cataract, dislocation or subluxation of the crystalline lens, dislocation of posterior chamber IOLs (PCIOLs), as well as for replacement of problematic anterior chamber IOLs (ACIOLs) or PCIOLs.
Method
Our suture material of choice is the Ethicon single-ended 10-0 polypropylene (Prolene) on a curved CIF-4 needle, two of which are required. The CZ70BD is a single-piece, biconvex IOL made of polymethylmethacrylate. It has 2 haptics, each with an eyelet, an optic diameter of 7 mm, and overall length of 12.5 mm.
Our technique for 2-point transscleral fixation using a modified cow-hitch suture is as follows.
INITIAL INCISIONS
- Localized appropriately placed conjunctival peritomy is performed.
- Two partial-thickness triangular limbal-based scleral flaps, approximately 2.5 to 3.0 mm per side, are created 180 degrees apart using a crescent blade at the sites for suture fixation. The preferred positions are 6 and 12 o’clock, but individual case anatomy and prior surgeries may require placement elsewhere around the limbus, as illustrated in Figure 34-2. Larger blood vessels should be avoided.
- If clinically indicated, a 3-port pars plana vitrectomy is performed at this point.
- Using a 25-gauge needle, a scleral tunnel through to the ciliary sulcus is created under each scleral flap, 1.25 mm posterior to the limbus.
- A small initial corneal incision is made with a keratome blade in an adjacent superior limbal corneal position as depicted in Figure 34-2.
Figure 34-2. Two partial-thickness scleral flaps are made 180 degrees apart. The initial limbal incision is small, as indicated by the solid line, and is later expanded along the dotted lines to allow implantation of the lens. One needle is inserted suture-end first through the scleral tunnel created within the scleral flap. A Kuglen hook is then used to retrieve a loop of the suture through the limbal incision while keeping the needle tip outside the eye.
INTRODUCING THE SUTURE
- Also shown in Figure 34-2, a 10-0 Prolene suture is delivered into the posterior chamber via the scleral tunnel, with the needle inserted blunt-end first. This end of the needle, into which the suture thread inserts, should be visible to the surgeon through the pupil. The pointed end of the needle should remain outside the globe.
- Using a Kuglen hook inserted through the corneal incision, a loop of the suture is captured and externalized. The length of suture pulled through should result in an approximately 15-mm loop protruding from the corneal incision to allow sufficient slack for tying to the eyelet and haptic, with the suture needle retrieved from its incomplete insertion so that the sharp may be placed away from the eye but still attached to the suture.
- This process is repeated with the second 10-0 Prolene suture through the opposite scleral tunnel.
- Using a Kuglen hook inserted through the corneal incision, a loop of the suture is captured and externalized. The length of suture pulled through should result in an approximately 15-mm loop protruding from the corneal incision to allow sufficient slack for tying to the eyelet and haptic, with the suture needle retrieved from its incomplete insertion so that the sharp may be placed away from the eye but still attached to the suture.
Figure 34-3. The CZ70BD lens is positioned in the operating field atop the eye and in the correct orientation. A small loop of the externalized suture is grasped from outside and underneath the haptic, then passed up and through the eyelet.
MODIFIED COW-HITCH SUTURE
- The CZ70BD lens is positioned in the operating field on an aliquot of viscoelastic in the orientation it will assume in the eye (ie, anterior surface face up and shoulders of the haptics leading clockwise).
- Using tying forceps, the externalized loop of the first 10-0 Prolene suture is brought to a fine loop point so that it can be threaded up and through one of the eyelets as show in Figure 34-3.
- The emerging loop tip is gently caught with another pair of tying forceps and pulled through for approximately 5 mm, taking care not to grasp or crimp the loop.
- As depicted in Figure 34-4, the forceps are then fed up and through the loop approaching from the optic side, so that the trailing double strand of suture is picked up and pulled back through the loop. This creates a second, now double-stranded loop as seen in Figure 34-5.
Figure 34-4. A pair of tying forceps is pointed through the loop and over the haptic to grasp the lagging double strand of the suture.
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