Tying a suture means forming a secure knot that holds tissue edges together without cutting into them. The most practical method for beginners is the instrument tie, which uses a needle holder to build the knot throw by throw. It’s the technique taught first in most surgical skills courses because it wastes less suture material than hand tying and gives you more control over tension.
The Instrument Tie, Step by Step
You need a needle holder (also called a needle driver) and a length of suture that has already been passed through the tissue. Once the suture is through, you’ll have two ends: a long end still attached to the needle and a short free end. Hold the long end in your non-dominant hand. The needle holder goes in your dominant hand.
Place the needle holder between the two suture ends, resting it flat. Wrap the long end around the needle holder once, moving away from you. Open the jaws of the needle holder and grab the short end, gripping it close to its tip. Pull the short end through the loop you just created. As you pull, use both hands evenly so the first throw lays flat against the tissue. This is your first half-hitch.
For the second throw, place the needle holder between the two ends again. This time, wrap the long end around the needle holder once in the opposite direction. Grab the short end through the loop and pull it through. Pulling evenly with both hands is critical here. Keep this second throw parallel to the first and slide it down so it sits snugly against it. If you pull harder on one side, the knot becomes lopsided and less secure.
After the second throw is seated, you can gently lift both ends upward and lower them again to snug the knot further. Do this smoothly. Jerking at this stage converts a square knot into a series of loose hitches that can slip under tension. Add at least one more throw for security, alternating direction each time.
Square Knot vs. Surgeon’s Knot
The two knot types you’ll use most often differ in just one detail: the first throw. A square knot uses a single wrap on every throw. A surgeon’s knot doubles the first wrap, creating a double overhand on that initial throw. Everything else stays the same.
That double wrap matters because it adds friction. The extra twist holds its position while you lay down the second throw, which is especially useful when you’re working with slippery monofilament suture or tying under tension. In laparoscopic and robotic surgery, many surgeons prefer the surgeon’s knot for the same reason: it stays put between throws. For braided suture materials that naturally grip well, a standard square knot is often sufficient.
How Many Throws You Need
The minimum number of throws for a secure knot depends on your suture material. Smooth, single-strand materials need more throws because they’re more prone to slipping. Braided materials grip against themselves and can get away with fewer.
- Polypropylene: three throws is secure across most sizes, making it one of the easier monofilaments to work with.
- Nylon (monofilament): three to five throws, depending on suture size. Coated nylon tends toward four or five.
- PDS (absorbable monofilament): three to four throws.
- Vicryl (braided absorbable): three to five throws.
- PTFE: six throws, the most of any common suture material.
The universal minimum is three throws for both square knots and surgeon’s knots. Fewer than three and you don’t have a reliable knot regardless of material. When in doubt, adding one extra throw is far safer than cutting corners.
Getting the Tension Right
The goal of every suture is to approximate tissue, not strangulate it. You want the wound edges to come together and just touch. If you pull too tight, the suture cuts into swollen tissue, causes more damage, and can actually break. If you leave it too loose, the edges gap open and the wound won’t heal properly.
Keep your hands close to the knot while you’re tying. When your hands drift too far from the tissue, it becomes much harder to feel how much tension you’re applying. You lose that tactile feedback and risk either overtightening or leaving slack. Controlled, short movements near the knot site give you the most precision.
When closing a wound under significant tension, a sliding knot technique can help. You build the first throw as a slip knot, slide it down to the desired position until the wound edges meet, then lock it with square throws on top. This gives you controlled, sustained tension without having to muscle the knot into place.
Common Mistakes and How to Avoid Them
The Granny Knot
A square knot requires that you alternate the direction of your wraps with each throw. If you wrap the same direction every time, you create a granny knot, which looks like a knot but doesn’t hold. The visual cue is that a square knot lies flat, with the loops stacking neatly on top of each other. A granny knot twists and sits crooked. The fix is simple: cross your hands (switch which end is on top) between throws.
Air Knots
An air knot happens when you don’t slide each throw all the way down to the tissue surface. Small gaps form between the loops, leaving the knot loose even though it looks complete from above. The result is a closure that doesn’t actually hold the tissue together. After each throw, make sure the loop is fully seated against the previous one before starting the next.
Uneven Pulling
Pulling harder on one strand than the other shifts the knot off-center and weakens it. Both hands should move symmetrically, applying equal force. This is one of the hardest habits to develop because your dominant hand naturally wants to do more work. Practicing with both hands moving as mirror images builds the muscle memory.
Breaking the Suture
Excessive tension during tying can snap the suture entirely, especially with finer gauges. If you find yourself pulling hard to get tissue edges together, the solution isn’t more force. It’s a different closure strategy: undermining the wound edges, placing deeper tension-relieving sutures, or choosing a stronger suture size.
Cutting the Tails
Once your knot is complete, cut both suture tails at the same time using scissors designed for suture or the cutting surface built into some needle holders. Cutting both together avoids putting tension on just one strand, which could loosen the knot. Leave the tails long enough that the knot won’t unravel. For skin closures, tails of about 3 to 5 millimeters are typical, though slippery monofilament materials benefit from slightly longer tails since they’re more prone to slipping.
The number of throws matters more than tail length for knot security, but cutting tails too short negates the work you put into building a solid knot. When you’re learning, err on the side of leaving tails a bit longer until you’re confident in your knot quality.