Creep vs Stress-Relaxation
Stress-relaxation is a corollary of the more common term, “creep”. When skin is put under force or tension by internal or external tissue expanding “devices”, it stretches (creeps). There are two forms of creep: mechanical and biological.
Mechanical creep occurs quickly (intraoperatively), within minutes to hours, and results in stretching or lengthening of the skin because of the breakdown of the dermal framework. For example, polypropylene suture will creep (and eventually break) when under increasing amounts of tension.
Biological creep occurs over weeks to months (staged tissue expansion) and is the result of the production of new tissue and recruitment of surrounding tissue. The stretching of abdominal skin in pregnancy is an example of biological creep.
Not only does the skin elongate (mechanical creep) when enough force or tension is applied, but the force required to maintain that stretch of the skin reduces over time. This reduction of force (i.e. tension of skin around a defect) required to maintain a stretch is the property of stress-relaxation.
When repairing surgical defects, wound closure tension is more important than wound closure size. Most people are aware that a large wound in one part of the body may be very easy to close, while the same size wound in another part of the body may be under too much tension to approximate. For example, a 2.5cm wide wound on a calf may be relatively easy to approximate, while the same size wound on the shin could be very difficult. Thus, when discussing methods to facilitate wound closure, it is customary to discuss “stress relaxation” rather than creep.
How does the SUTUREGARD ISR Device help with Creep and Stress-Relaxation?
The SUTUREGARD Intraoperative Skin Relaxation (ISR) device is a suture bridge that allows large amounts of force to be applied to skin for the purposes of achieving mechanical creep and stress-relaxation of skin surrounding a wound without tearing the skin or damaging the wound edges.
You can think of the SUTUREGARD ISR Device like a snowshoe. Without a snowshoe, a person walking through deep snow with snow boots would sink into the snow. With the snowshoe, the boot’s surface area is increased thereby decreasing the pressure of the boot on the snow, allowing the person to walk on top of the snow.
Prior to the SUTUREGARD ISR Device, devices to create mechanical creep and stress-relax skin were more cumbersome and involved more skin punctures to the skin.