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Suturing and knot tying technique
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Basics of surgical knot tying
Surgical knots may be tied with one hand or two hands. When tying the surgical knot with one hand, one hand applies constant traction on one limb, while the other hand ties a throw or loop with the other limb of the suture. In the two-handed technique, both hands tie the knot equally and thus create a more direct and secure knot (see surgical knot video). The drawbacks of the two-handed technique are the lack of traction on both limbs of the suture and the fact that it is more difficult to learn.
The single-handed technique alternates between knot tying with the index and the middle finger. Knot security is achieved by switching the hand/suture limb applying the traction.
The benefits of this technique include faster tying speed, continuous limb traction (particularly useful when tying at depth, e.g., in the lesser pelvis) and ease of learning. As a rule, only two overlaid loops (i.e., two throws) will lock the knot. Final seating of the first two throws is achieved by alternating the hand/limb applying the traction. The first throw determines the traction on the tissue, while the second locks the first.
The following video sequences illustrate the basic techniques for single-handed knot tying from the perspective of a right-handed surgeon. Here, the "traction limb" is always in the left hand and the "knot tying limb" in the right hand.
Knot tying with the middle finger
Grasp the suture limbs between index finger and thumb . The limb to be used for tying must first cross under the traction limb to avoid an overthrow which would impair knot security. With the right hand in supination (palm facing up), place the middle and ring fingers on the knot tying limb. At the same time place the traction limb on the middle and ring finger of the right hand. With the bent right middle finger pull the knot tying limb behind the traction limb. While the thumb and index finger of the right hand release the knot tying limb, fashion the throw by anchoring the knot tying limb with the middle and ring fingers stretched out once again and then pulling it behind to the right. And finally, with the right index finger push the throw down along the traction limb.
The example demonstrates the base throw with two follow-on throws, with the last throw achieving reversal by alternating the hand applying the traction. A total of 4 throws are recommended with braided sutures. When tying the last two throws, alternate the traction limb / hand applying the traction. 6 to 8 throws are recommended with monofilament sutures. To achieve reversal and thus secure knots after the first two throws, tie all other throws by alternating the traction limb / hand applying the traction.
Note: Alternatively (not illustrated in the video), crossing the hands after tying the throws will avoid overthrown knots.
Index finger knot tying
With the hand applying traction, grasp the limb of the suture with thumb and index finger, while the knot tying hand grasps the other limb with thumb and middle finger. The suture limb used for tying now first crosses over the traction limb to avoid overthrowing. Load the knot tying limb onto the index finger and then guide this finger over the traction limb. This creates an "opening" between both limbs. Now bend the index finger of the tying hand such that its tip can be brought behind the tying suture limb. By straightening the index finger again, this will pull the tying limb forward out through the opening. Then anchor the tying limb between the index and middle finger and fashion the throw by moving the right hand sideways. Finally (not illustrated in the video sequence), push down the throw again along the traction limb.
The example demonstrates one base throw and two follow-on throws, with the last throw achieving reversal by alternating the hand applying the traction.
Note: In the video sequence, the overthrown knot is not pushed down since this would not provide secure seating. Here, too, the alternative of crossing the hands after tying the throws will avoid overthrown knots.
The square knot is the surgeon's most reliable knot. It is fashioned in single-handed technique by combining both throws shown above, guided by the middle and index finger, respectively. Reversing both throws placed on top of each other will lock the knot.
The first throw determines the traction on the tissue, while the second provides knot security.
Knot security can be improved even further by adding additional square knots.
Note: A higher number of throws (approx. 6 to 8) can compensate for the poorer knot security of monofilament suture material.
Combining both throws presented above, guided with the middle and index finger respectively, the slip knot is a single-handed technique particularly suitable for tying at depth, since the suture is under constant traction, thus ensuring good knot security. Fashion the first two throws using the same technique (guiding with middle and index finger respectively). Depending on the chosen technique, crossing over or under is only necessary the first time. This creates two parallel throws, which are pulled tight along the traction limb, but can also come loose again; they can therefore slip. The first two throws are then locked in position by a reversed throw. In the example shown, the throw tied with the index finger locks the two preceding throws tied with the middle finger. Follow this with two more throws tied with the middle finger while alternating the traction limb / hand applying the traction. This finally secures the knot.
Whereas this also combines throws tied with the middle and index finger, here both techniques are performed simultaneously. This immediately creates two throws, which are already quite secure, with final security being provided by a third throw. The surgeon's knot lends itself quite well, for example, for securing drains and central lines.
Handling of suture instruments and principles of skin suturing
Grasp the forceps like a writing implement. Tissue forceps help avoid bruising of the skin edges, which otherwise might impair wound healing.
The video example uses a Hegar-Olsen needle holder, with the thumb and ring finger passing through both ring handles. Rest the middle finger on the ring handle where the ring finger is inserted and place the index finger on the shanks for guidance. If possible, guide the needle holder solely with the distal phalanges of the fingers.
Handle scissors in the same fashion.
The needle holder should clamp the needle approximately one-third the distance from the shank to the tip of the point, but never over the shank, since the latter represents a given breakaway point for the attached suture.
Do not clamp sutures, particularly monofilament types, with the needle holder, as this will cause microdamage and decrease tensile strength. For knot tying, clamp the suture with the needle holder far distad in a section that will be clipped later.
Always try to suture toward you. The usual spacing between two stitches is between 0.5 cm and 1.5 cm. Larger spacing will leave sections of the wound gaping, thus promoting contamination.
The tissue entry and exit points of a skin suture must be far enough from the edge of the wound to prevent tearing and not impair the blood supply to the wound edges. The stitches should be 5 mm to 7 mm away from the edges of the wound. Edematous wounds and those under tension may require greater spacing.
The needle should penetrate the skin at right angles, rather than tangentially, and the needle design used should reflect the wound situation. The needle should exit the tissue in the middle of the wound and pierce the contralateral side anew. Distorted wound edges are best prevented by having the needle exit the tissue exactly opposite its point of entry.
Interrupted sutures and instrument ties
The most common type of surgical skin closure are interrupted sutures tied with the instruments already in the hands of the surgeon. They are straightforward to fashion and provide reliable seating. The following should be noted:
- Needle entry into and exit from the tissue should at the same distance from the incision, with the bites taking equal amounts of tissue
- always penetrate the skin with the needle at right angles
- maintain equal spacing between stitches.
For instrument ties, first place the needle holder between the two limbs of the suture. Then wrap the limb with the needle twice around the needle holder, which then grasps the other limb far distad. Now pull the needle holder toward you and the limb with the needle away from you. This will result in a fully secured knot without overthrowing.
By tying the knots away from the edges of the wound, they will rest on the skin rather than the wound itself.
Next, wrap the limb once around the needle holder and tie the throw in the reverse direction of the first throw. Fashion the third throw in the same way. The change in direction is mandatory to achieve truly reversed throws. Depending on the suture material and situation, repeat the sequence for all other throws.
Clip both limbs of the suture five to seven millimeters from the knot.
Note: When tightening the throws, pull only on the long limb of the suture.
Donati-McMillen vertical mattress suture
The vertical mattress suture, first described by Donati and McMillen, is more stable than interrupted sutures and can withstand greater tension. It starts the same way as interrupted sutures. The strictly intradermal back stitch away from the surgeon is in the plane of the first stitch. After each stitch, pull the (monofilament) suture all the way through the tissue; if it done at the very end, the suture will cut through the four penetration points of the needle with unwanted force. While this suture will improve wound edge approximation compared to interrupted sutures, it penetrates the skin four times. Fashion the instrument tie as described above.
Allgöwer vertical mattress suture
Wound closure with topical adhesives
Wound closure with tapes
Stapled wound closure