Suture diameter
The most basic principle for selecting sutures is to use sutures that are as thin and strong as possible and have minimal reaction to tissue. The thickness of various sutures is indicated by numbers and zeros. The larger the number, the thicker the sutures; the unit of the diameter of the sutures is millimeters, often expressed as a few 0s. The thinner the suture, the greater the number of 0s. For example, six zero nylon threads are thinner than four zero nylon threads. But the actual thickness depends on the material of the suture. For example, with the same 5 zeros, the bowel thread is thicker than the polypropylene synthetic thread (ProleneTM). The principle of choosing the thickness is that, as long as it can withstand the tension of the wound, the suture should be as thin as possible.
tensile strength
The US National Pharmacopoeia (USP) defines tensile strength as the minimum strength that can pull a single suture. Therefore, the tensile strength refers to a specific tension value, but a non-linear interval. Effective tensile strength refers to the tensile strength after the stitches are looped or knotted. The tensile strength of the same type of suture after knotting is 1/3 of its unknotted. In general, the suture of synthetic material is greater than that of sheep intestine, and the tensile strength of tendon suture is greater than that of synthetic material.
structure
The structure refers to whether the suture is single strand (monofilament) or multiple strand (braided thread). Multiple strands of stitches are woven. Such sutures are easy to handle but increase the chance of infection and tissue reaction. It is easy to cause infection because of its siphon effect to allow bacteria and foreign matter to penetrate. Bacteria buried deep inside the braided thread can escape the host macrophage phagocytosis. Therefore, monofilament thread (nylon or polypropylene) is more suitable for suturing contaminated wounds. However, the monofilament thread is not easy to handle.
Coefficient of friction
The friction coefficient of the suture determines whether the suture easily passes through the tissue. Sutures with a low coefficient of friction (such as polypropylene sutures) can easily slide through tissues, so they are often used for intradermal sutures. The lower the friction coefficient, the smoother the suture and the easier the thread knot to loosen. Therefore, when using polypropylene sutures, it is often necessary to tie a few more knots.
Knot firmness
The knot strength refers to the minimum tension to loosen the knot, which is proportional to the friction coefficient of the suture. The greater the knot strength, the less likely the wound will split. Suture knots with high friction coefficients have good firmness, but they have high resistance when passing through the skin and are not easy to use.
elasticity
Elasticity refers to the ability of a suture to return to its original length and shape after being stretched by a wound swelling. Sutures with better elasticity (such as NovafilTM polybutylene synthetic thread) are not easy to cut the tissue when the tissue is edema, and it does not loosen after the edema subsides, and the wound is not easy to split.