Suture Needles

The needle is half the device

A suture is sold as one product and is really two things joined together. The strand is a material question — what it is made of, and what becomes of it. The needle is a mechanical one — how the strand is carried through tissue and where it can be turned.

They are chosen on different grounds, which is the practical point of this page. The same polyglactin is offered on a dozen needles because the material decision and the needle decision are independent. A clinician who has settled on a material has not yet settled on a needle.

Three regions, specified separately

A surgical needle is one piece of steel, but it is described as three regions, and they answer different questions.

The point is the tip geometry: how the needle parts the tissue in front of it. The body is the length between the point and the far end — it carries the curvature and it is the section a needle holder grips. The swage is the end the strand is joined into.

Naming them separately is not pedantry; it is how a needle is ordered. A code states a point geometry, a curvature and a length, and those three are chosen independently of one another and independently of the suture material attached. That is why the same polyglactin appears against a dozen different needle codes.

Swaged, and what the bore is for

Modern sutures are swaged: a bore is drilled into the needle’s end and the strand is closed into it, so needle and suture form one continuous unit. There is no eye and nothing to thread.

That bore is annealed — heat-treated to soften it — before the strand goes in. A needle body is hardened steel; a hardened bore would crack rather than close when crimped onto the suture. So the two ends of the same needle are deliberately different: hard where it must hold its shape, soft where it must be deformed.

The older name for a swaged suture is atraumatic, from the contrast with a threaded eyed needle, which drags a doubled strand through the tissue behind it.

Points

The point decides how the needle gets through tissue, and there are only two answers to that: spread it, or cut it.

A taper point is round in cross-section and narrows to a tip. It spreads tissue apart as it passes, parting fibres rather than severing them. A cutting point is triangular and carries an edge. A blunt point is round with a rounded tip.

The distinction that the figure above makes clearest is the one that the names hide. Turn it to Conventional cutting and then to Reverse cutting: both are triangular, and both cut. What differs is where the edge sits. On a conventional cutting needle the edge is on the inside of the curve — the concave face. On a reverse cutting needle it is on the outside, the convex face, pointing away from the curve’s centre. That single difference in cross-section is the whole distinction between the two, which is why the names are so easily transposed and why the geometry is worth looking at rather than memorising.

Which of these belongs in which tissue is a clinical judgement, and the approved combinations are in the instructions for use.

Curvature

Needle curvature is given as a fraction of a circle — 1/4, 3/8, 1/2, 5/8 — or straight.

Every curvature in the figure is drawn at the same arc length, which is the point of showing them together: what changes between them is how tightly the same length of needle is turned, not how much needle there is. A flat drawing usually makes the tighter curves look shorter, and that is misleading.

The arc governs how the needle can be rotated through tissue in the space available. A needle is driven by rotating it about the centre of its own arc, so the curve sets the path the point travels and the room the wrist needs to complete the turn. A shallower arc sweeps a wider, flatter path; a tighter one comes back around within a smaller footprint. A confined or deep field constrains how much curve is usable, and a straight needle is pushed rather than rotated at all.

Curvature is independent of point geometry and of the strand: any of the points above can be supplied on any of these arcs, which is exactly why a code has to state both.

The steel

Needles are made from stainless steel in two families: the 300 series and the 420 series. They are different alloys and they respond differently to heat treatment, which is why a needle range uses both rather than settling on one. The difference between the two alloy families is its own subject.

That difference is not abstract: it is what makes the swage possible. The bore has to be softened enough to be closed onto a strand while the rest of the needle stays hard enough to hold its curve, so a single needle is deliberately not uniform along its length — and how an alloy answers to that treatment decides which family a given needle comes from.

Lengths run 16 mm to 90 mm in the 420 series and 30 mm to 50 mm in the 300 series. After forming, needles are electro-polished — an electrochemical surface finishing step — and siliconized. Both are surface treatments applied to the finished shape, not changes to the alloy underneath.

Dolphin Sutures needles are manufactured by Futura Surgicare Pvt Ltd, which also makes the suture range.

Finding the needle on a given product

A needle is specified by three things at once — its point, its curvature and its length — and a product code states all three. Every product page carries an ordering table, and every code in it gives the needle profile and the needle length supplied against that code.

That table is the answer to “which needle comes with this suture”. This page is the answer to “what are the choices, and why do they exist” — and the two questions are worth keeping apart, because a code is a fact about what is supplied, while the choice between geometries is a clinical judgement that belongs with the surgeon and the instructions for use.