The mattress suture is a common stitch used to close wounds. It is an interrupted stitch, which means that each stitch is tied off before creating the next stitch. It is strong and can be used to close relatively wide wounds. There are two basic variations: the vertical and the horizontal.
The vertical mattress includes two deep penetrations, or bites, and two shallow bites, all on the same vertical line, which is perpendicular to the wound. The suture enters the tissue, passes under the surface of the tissue and through the wound and exits on the other side. The two shallow bites are made first, followed by the deep bites, returning to the side of the wound where the needle first entered, so that the ends can be tied off. Both the vertical and the horizontal mattress suture are typically tied using a square knot.
Since it actually has two anchors in both the deep and shallow penetration, along the same linear path, the vertical mattress suture has excellent tensile strength. A good surgeon will create even, symmetric stitches, piercing the tissue with the same depth and width from the wound. Irregular stitches can result in additional scaring.
The horizontal mattress suture requires four deep penetrations, in a rectangular pattern, with each bite marking the corners of the rectangle. It is sometimes used as a basting stitch to hold the tissue at its proper location so that other interrupted sutures can be made. In such a case, the horizontal stitch would be removed after the other stitches are in place.
A variation of the horizontal mattress stitch is the half-buried horizontal stitch. It is commonly used to close angled wounds. In this case, the suture enters the tissue outside the point of the wound, follows a curved path encompassing the entrance point and sides, and exits the tissue close to the entrance point. The suture forms the shape of a circle under the tissue, with only the tied off ends on the outside.
Both the horizontal and vertical stitches pose a risk of strangulation if they are tied too tightly. Bolstering the stitches, or supporting them with small pieces of material, can reduce strangulation, as well as removing the stitches as early as possible. The tightness of interrupted stitches can be adjusted in each individual suture, which is especially important for irregular lacerations.
It is common for the mattress suture to leave some scarring. The shape of the scar is sometimes called "train tracks" because the suture leaves a line of scar tissue accompanied by prick marks where the needle entered and exited the tissue. If possible, the mattress suture is removed within five to seven days to reduce scarring.