Tying an instrument knot

What it is

The instrument knot is how most skin stitches are tied: the suture is wrapped around the needle holder, which then grasps the short end and pulls it through the loop. It saves suture, works in small spaces and is the knot examiners expect in a suturing station. A secure knot is a square (reef) knot: each throw lies flat and is tied in the opposite direction to the one before. If successive throws go the same way, the result is a granny knot that slips. The first throw is often a double wrap (a surgeon's throw), whose extra friction holds the edges together while the second throw is laid. Monofilament sutures are slippery and springy, so they need more throws than braided ones. The skill is in laying each throw down flat with even pull on both ends, without crushing the part of the suture that stays in the skin.

Indications

• Tying every interrupted, mattress or anchoring stitch of a skin closure.
• Closing in small or deep spaces where hand ties are awkward.
• Saving suture length: the instrument knot can be tied with a short free end.
• OSCE suturing stations, where a secure square knot laid to one side is marked.

Contraindications and precautions

• Never grasp the part of the suture that will stay in the tissue with the instrument: crushing weakens it.
• Do not saw or jerk the throws: uneven pull converts a square knot into a slip knot.
• Do not over-tighten the first throw: the stitch must approximate, not strangle, the edges.
• Keep the needle under control during the knot to avoid a needlestick; hold it away from your fingers and the patient.
• Fine sutures break if pulled hard; very slippery monofilament needs extra throws to be secure.

Equipment

• Needle holder (instrument) and toothed fine forceps.
• Suture scissors.
• The suture already passed through the wound, with a short free end and a long end carrying the needle.
• A practice pad for learning, sterile gloves and field for patients.

Step by step (and why)

1. Pull the suture through until a short tail remains on the far side — a short tail is easy to grasp and saves suture.
2. Hold the needle holder parallel to the wound, between the two ends — this sets up the wraps and lays the knot flat.
3. Wrap the long end twice around the tips, away from you — a double first throw (surgeon's throw) holds without slipping.
4. Grasp the very end of the short tail and pull it through — grasping only the tip avoids crushing the suture that stays.
5. Lay the throw flat by pulling the ends in opposite directions across the wound — the hands cross, and the throw sits square.
6. Snug the throw just until the edges meet — tissue swells, so a tight first throw becomes a strangling stitch.
7. Wrap once in the opposite direction, grasp the tail and lay it flat with the hands back — reversing makes a square knot, not a granny.
8. Add further single throws, alternating each time — monofilament needs more throws than braided suture to stay secure.
9. Move the knot to one side of the wound and cut the tails, leaving enough to grasp at removal — knots on the wound line irritate it.

Complications

• Slipping or untied knots from throws in the same direction (granny knot) or too few throws for the material.
• Suture breakage from crushing with the instrument or pulling too hard on fine sutures.
• Strangulation of the tissue from an over-tight first throw: blanched edges, pain and later necrosis or marks.
• Tails cut too short (the knot unties or cannot be grasped at removal) or too long (they tangle in the wound).
• Needlestick injury while handling the needle during tying.

Next step

• Check each knot before cutting: square, flat, to one side and holding the edges together without blanching.
• Practise on a pad until the throw direction is automatic; examiners watch the alternation.
• If a knot slips during closure, remove that stitch and replace it rather than adding throws to a loose loop.
• Explain to the patient when and where the stitches will be removed.

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Elsewhere in DurgiPedia

• Removing sutures and staples

Connections

← All clinical skills

Educational content; it does not replace supervised hands-on training, your institution's protocols or a prescriber's order. A procedure is learnt with a teacher and done only once you are trained to do it.

Sources: Wound Closure Techniques (StatPearls (NCBI Bookshelf), 2023).

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Representative model, for educational purposes only.