During training, needles are least talked about and most of us remain ignorant about the basic features and specific uses of the various types of needles. Only the members of the surgical team handling and dissecting the tissue have an idea of the texture of the tissue and the strength required to pierce it with minimal trauma. The needle point initiates penetration at the desired region and the rest mechanism consists of tissue separation along the path making way for the attached suture. Surgical needles have a needle-point front, a body, and a back portion. The suture is connected to the back end of the needle with the rest trailing, The manner in which the suture is connected is interesting – previously there were eyes posteriorly through which one end of the suture had to pass; this is the classical system, and the French modification was to have a springy divided back-end through which a suture end is forced.
The pointed needle front penetrates the tissue followed by the body and then the thread is swaged into the back end of the needle. The profile in the cut section depends upon the toughness and texture of the tissue the needle will have to encounter. Thus, a needle may be round-bodied for softer tissue and flat lance-like for cutting through tissue–cutting needles, these may be a conventional or reverse cutting (vide figure).
Needles may be curved or straight. The curve can be simple or compound and the easiest way to penetrate a tissue is to present the needle point at right angles to the surface of the tissue to be pierced. Prior planning, imagination, and visual ideation by the operating surgeon are important for this. Penetration by the needle tip becomes easiest when the tip encounters the tissue at right angles to the tissue to be penetrated.
Surgical needles are conventionally made from high-strength martensitic Tungsten-Rhenium stainless steel alloys such as AISI type 420, ASTM 45500, etc. Ethalloy is a proprietary alloy of Ethicon, Inc. used to make surgical needles. The use of this strong and non-brittle material ensures smooth passage through tissue. Fragmentation and breakage only happen in extreme conditions and minimum trauma during passage is ensured
There are specific surgical instruments - a needle-holder - for gripping a needle during surgery: --
1. Straight needles are mainly manipulated by hand.
2. Big needles need stout needle holders.
3. Cutting needles are for tough and calcific tissue - conventional and reverse cutting - the choice depends on the surgeon and the type of tissue he encounters.
4. Round-bodied needles negotiate softer tissue better.
5. A grip at the 2/3rd-1/3rd junction with the tip pointing forward is recommended for curved needles. The larger portion of the needle is always in front of the grip region and
Tungsten-carbide lipping is often added to the inner surface of the blades of a holder consolidating the hold.
6. Castroviejo needle holders are for smaller curved needles and finer suture manipulations.
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