The instrument tie is a foundational skill used to secure suture material after placing stitches through tissue. This technique is valuable in surgical environments where the wound is deep or narrow, making it difficult or impossible to perform a hand-tied knot. The instrument tie allows a surgeon to manipulate the suture ends precisely over a distance. Mastering this technique is required for effectively closing a wound and providing the necessary mechanical stability for healing.
Essential Tools and Setup
The primary tool for this procedure is the needle driver, which provides the mechanical advantage to grasp and manipulate the suture ends. A proper grip is established by inserting the thumb and the ring finger into the instrument’s rings, known as the conventional or tripod grip. The index finger rests near the instrument’s hinge, allowing for precise control and stabilization during the tie.
Before beginning, the suture material must be passed through the tissue, leaving a long working strand and a shorter, non-needle strand, often called the “tail.” The needle driver is positioned horizontally and parallel to the line of the wound, centered between the two strands. Maintaining this parallel positioning helps prevent the formation of an asymmetric knot.
Executing the Standard Instrument Tie
Knot formation begins with the first throw, often employing a double wrap known as a surgeon’s throw. The long working strand is wrapped around the closed tip of the needle driver twice, typically away from the surgeon. This double wrap introduces friction, temporarily holding the first half-knot in place once tension is applied.
The needle driver then reaches through the loops to grasp the short tail of the suture. The instrument is pulled back through the loops, carrying the tail, while the non-dominant hand maintains tension on the long strand. The first half-knot is gently pulled down to the tissue level and seated against the wound surface.
The second throw immediately follows and is required for locking the knot into a stable square knot. For this throw, the long working strand is wrapped around the needle driver only once, and the direction of the wrap must be reversed from the first throw. For example, if the first wrap was clockwise, the second must be counter-clockwise to ensure the knot lays flat.
The needle driver grasps the short tail through the single loop and pulls it back through, moving the tail in the opposite direction from the first throw. This reversal ensures the second half-knot seats directly on top of the first, creating the parallel configuration of a secure square knot.
Securing the Knot and Troubleshooting
To complete the surgical knot and prevent slippage, additional single throws are required beyond the initial two throws that form the square knot. The number of additional throws depends on the suture material; slippery monofilament sutures require more throws than braided sutures. Each subsequent throw is a single wrap that alternates direction to maintain the square configuration.
Proper tension management is required for a successful instrument tie. The surgeon must pull the knot horizontally, parallel to the wound line, to gently approximate the tissue edges. Sufficient tension must be applied to bring the tissue together without causing tissue strangulation, which could impair blood flow.
A common error is failing to alternate the direction of the wraps, resulting in an asymmetric granny knot. Unlike a square knot, a granny knot is mechanically unstable and prone to slipping or unraveling, risking wound separation. Another error is the formation of a slip knot, where the strands slide instead of locking down flat. These errors are corrected by ensuring that all subsequent throws are pulled in the exact opposite direction of the preceding throw, ensuring the knot layers lay flat and parallel.