Keloid Surgery: How Undermining Reduces Tension on the Suture Line

What is a keloid, and how does it differ from an ordinary scar?

A keloid is a raised scar formed when collagen and other scar tissue accumulate excessively during healing. It can follow relatively small injuries — acne, a surgical incision, ear piercing, an injection or trauma — and appears most often on the chest, shoulders, jawline and earlobe, sometimes growing larger or firmer over time.

An ordinary scar usually stays within the boundary of the original wound; a keloid can extend beyond it into normal skin. The surface may be red or darkly discoloured, and itching or discomfort can occur when clothing rubs it.

A keloid is more than an uneven surface. Because the tissue proliferates excessively, correction should consider how the surrounding skin moves and what force the suture line will carry, not only removing what is visible.

A review of keloids and hypertrophic scars describes both as arising from chronic inflammation in the deep dermis, with tension on the skin amplifying that inflammation.^[1]

Read alsoWhy keloids differ by site is covered in “Keloid scars: why the ear and the chest behave differently” (Korean).

Why does tension matter in keloid closure?

Closing a wound means bringing the two skin edges together. If there is not enough skin available or the surrounding tissue is firmly fixed, the edges must be pulled strongly — that force is suture tension.

When tension concentrates on the suture line, the skin is pulled and the closure is under strain. On the chest and shoulders, where skin moves and stretches constantly, force is repeatedly transmitted to the line. Scar revision therefore needs to create the conditions for the edges to meet without force, not just close the wound.

Since keloids involve excessive proliferation, reducing tension at the closure is one of the factors considered in managing the scar afterwards. Releasing the surrounding tissue so the edges come together naturally, rather than dragging them, reduces the force concentrated on the line and the pull on the skin.

In a systematic review of seven studies comparing adjuvant treatment after keloid excision, recurrence with excision alone was reported at nearly 100% — which is why surgery is always planned together with adjuvant treatment.^[2]

What is undermining?

Undermining is a technique that separates the tissue beneath the skin edge from the surrounding tissue to give the skin room to move. After the scar is excised or the wound refreshed, the underside of the skin edge is dissected only as far as needed, creating space for the skin to come together naturally.

In plain terms, it is not merely matching the surface edges but creating space so the tissue beneath can move. If the skin edge is firmly adherent to deeper tissue, closure demands strong force; with undermining, the edges can be closed without excessive pulling.

The key is not to dissect widely regardless. The extent is set by the scar's location and size, skin thickness and the state of surrounding tissue, with the aim of reducing force concentrated on the suture line — easing pull and helping the skin settle into a natural position.

How is undermining performed?

Details vary with the scar and the extent of surgery, but the principle is to secure movement of the skin edge and then close with reduced tension.

First, the size, depth and location of the scar and the elasticity and mobility of surrounding skin are assessed. The direction in which the skin is pulled and how much force the edges will carry after closure are reviewed to plan surgery, along with the extent of excision and the direction of closure.

Next, the scar tissue is trimmed where needed and the tissue beneath the skin edge is dissected, creating enough slack for the two edges to approach without strain. Securing movement from below rather than dragging the surface is the core step.

Finally the edges are aligned and closed, adjusting position so the skin is not over-stretched or pulled to one side. Undermining provides the slack the closure needs and reduces the force applied to the skin.

What change can undermining produce?

The main advantage is reducing tension concentrated on the suture line. With movement secured beneath the edge, the burden of pulling the skin hard during closure is lower.

• Less pull at the closure: reducing the force dragging the edges together lowers tension on the line.
• Less skin distortion: it can help reduce the skin being drawn to one side or the area around the line dimpling.
• More natural edge apposition: securing tissue movement helps both sides meet without strain.
• Less burden on the closure: lowering the force applied to skin reduces strain in closing the wound.
• Support for scar management: it can help reduce the risk of the scar widening under tension.

How does undermining reduce pull?

If the edges cannot move sufficiently during closure, force concentrates at the skin surface; closing in that state can pull the surrounding area or distort the natural contour. Undermining aims to reduce that burden by securing movement beneath the skin.

Where the skin is firmly fixed, the edges must be pulled hard to meet; with space created by undermining, the range in which the edge can move widens and excessive force is no longer necessary. That can ease pull around the suture line and reduce distortion of the contour. Tension management also matters during recovery: keeping repeated force off the closure helps the wound heal stably.

Recovery and scar care after undermining

After scar revision including undermining, the closure should be allowed to heal without excessive force; dressing and wound care follow your surgeon's instructions.

Before healing, movements that pull hard on the line and repeated friction should be limited. On the chest or shoulders, even ordinary movement transmits force to the closure, so activity restrictions matter in the early period.

Once the wound has stabilised, scar measures such as silicone gel or sheets and pressure therapy can be applied as directed. If the scar thickens again, becomes markedly red, or itching or pain appears, early assessment is advisable. Keloids can regrow even after surgery, so size and thickness should be monitored for a period after healing — which is why a tension-reducing technique and post-healing care belong together.

In 38 patients who used a continuous tension-reduction device for more than six months after keloid excision, followed for 24 months, recurrence was 7.9% — achieved through tension management alone, without radiotherapy.^[3]

What should be checked before undermining?

Undermining is not applied uniformly to every scar operation. Its use and extent are decided from the scar's size and location, skin elasticity, the extent of excision and the tension expected at closure. How and how far to dissect is planned around the structure and state of the site.

Keloids can grow beyond the original wound and may recur after correction, so the growth pattern, previous treatments and the direction of skin pull should all be reviewed when planning. Undermining is a technique for lowering suture tension — distinct from, and additional to, managing recurrence risk.

After surgery, healing should be confirmed and any re-thickening or new symptoms watched for. Linking preoperative skin assessment, closure method and post-healing care is what scar correction requires.

Keloid surgery: common myths and facts