The locking technique confers two important advantages over the traditional horizontal mattress suture. First, the standard horizontal mattress suture does not typically permit the same degree of wound-edge apposition as can be accomplished with other transepidermal sutures, since the everting effect of the suture technique may be associated with a small degree of gaping at the center of the horizontal mattress suture. Locking the suture material brings the knot, as well as the two parallel external rows of suture, to the center of the wound, thus improving wound-edge approximation.
Second, suture removal with the standard horizontal mattress technique may be challenging, particularly if sutures are left in situ for an extended period of time and some of the suture material has been overgrown by the healing epidermis, as the knot may be buried in the context of a ridged everted repair. Bringing the knot, along with the parallel rows of external suture material, centrally with the locking technique allows the knot to be more easily grasped at the time of suture removal.
A modification of this technique has also been described, where instead of passing the needle under the loop of suture, the loop is instead incorporated into the knot, thus increasing economy of motion. For this modification, a loop is left as described previously and all steps are followed through step (5). Then, the end of the suture with needle attached is looped twice around the needle driver and the tip of the needle driver is passed through the loop to grasp the tail of suture. Once the suture tail is pulled, the horizontal mattress suture becomes locked.
As with most transepidermal techniques, it is important to enter the epidermis at 90 degrees, allowing the needle to travel slightly laterally away from the wound edge before fully following the curvature of the needle when utilizing this technique. This will allow for maximal wound eversion and accurate wound-edge approximation.
As with the simple interrupted suture, care should be taken to avoid skimming the needle superficially beneath the epidermis. This results from failing to enter the skin at a perpendicular angle and failing to follow the curvature of the needle. This may result in wound inversion as the tension vector of the shallow bite pulls the wound edges outward and down.