Suture and needles

Characteristics of the needle

• Needles can either be round bodied or cutting and this term is a description of the profile of the needle in cross-section. They also come in different sizes (measured in millimetres) and shapes (straight, half-curved and curved).
• The species and size of animal and purpose for which the needle is required will dictate the size, shape and cross-section of the suitable instrument.
• Round bodied needles are designed to separate tissue fibres rather than cut them and are used either for soft tissue (such as fat) or in situations where easy splitting of the tissue fibres is possible (as in muscle). After the needle has passed through the tissue it closes tightly around the suture material forming a leak-proof suture line. A variety of more specialised round-bodied needles can be purchased for use in intestinal surgery or work with friable tissues such as liver.
• Cutting needles are required wherever tough or dense tissue (such as skin) needs to be sutured. Various types of cutting needle are available, but the conventional cutting needle is suitable for use in the majority of circumstances.
• Round bodied / cutting needles also exist such as the trochar point and the tapercut. Further details can be found in the Ethicon booklet “Suture Material and Surgical Needles in Veterinary Surgery”

Characteristics of Suture Materials

The ideal suture material would permit its use in any operation by having the following characteristics:

• Easy to handle and knots securely
• Promotes rapid healing by causing minimum trauma
• Holds the wound together and has a high tensile strength
• Disappears when its work is done
• Non-irritant
• Free from infectious agents.

No single suture material has all these properties and so a suture material must be selected which will be most suitable for the purpose for which it is required. With the suture material selected there will be variation in:

• Ease of handling/knotting
• Tissue trauma – ‘drag’ of the material as it is pulled through body tissues
• Strength
• Absorption profile – time of useful holding strength
• Tissue reaction – inertness of the material
• Potential for wicking / capillary action
• Cost

Absorbable sutures provide temporary support for the tissues in which they are placed. Absorbable suture materials cause a reaction in the tissues as the body’s defence mechanisms “see” them as a foreign body and enzyme processes break them down. These materials will gradually loose their strength as the body degrades them and so wounds are only supported for a limited time (referred to as ‘time of useful holding strength’).

Non-absorbable sutures provide permanent support for the tissues in which they are placed, they remain encapsulated within the tissues and will not be broken down. The body’s defence mechanisms may “see” them but are not capable of degrading them. Occasionally the body will react to buried non-absorbable material in a more vigorous way and a sinus will develop or the material will migrate and eventually be expelled by the body. If placed in the skin layers these sutures can (should) be removed.

Absorption profile – time of useful holding strength

The type of tissue to be sutured and the time it takes to heal will dictate the shortest period for which the suture must retain its strength and support the wound. The time a tissue type takes to heal will also vary between species, below are some examples relating to the tissues of dogs.

• Skin: 7-10 days
• Fat: 5-7 days
• Muscle: 14 days
• Fascia: 42 days
• Serosa / mucosa: 2-3 days