Skin of humans and animals is a non-homogeneous viscoelastic tissue with the combined characteristics of a viscous fluid and elastic solid. Skin extensibility is dependent upon three factors occurring consecutively as a load applied to the skin is progressively increased:

 Convolutions in dermal collagen progressively straighten.

 Dermal collagen fibres align parallel to each other in the direction of the applied load.

 Fully aligned collagen fibres extend only upon application of great increases in tension.

As skin progressively extends, it contracts in a plane at right angles to the applied load.

The inherent extensibility of the skin is subjectively assessed by gently grasping and lifting this skin between the thumb and index finger. Mechanical creep is the biomechanical property of skin allowing further extension of skin beyond the limits of its inherent extensibility. In mechanical creep, collagen fibres align, over time, with subsequent displacement of interstitial fluid surrounding the collagen fibres and fibrils which comprise individual collagen strands. Stress relaxation of the skin, the progressive reduction in force required to maintain the stretched skin's length, is a corollary of mechanical creep. Mechanical creep and stress relaxation can be achieved by application of a constant load to the skin or by intermittent stretching of the skin with periods of relaxation (load cycling). Biological creep has been recognised as the progressive increase in skin surface area that occurs when slowly expanding subcutaneous forces are applied to the overlying cutaneous tissues. Progressive enlargement of a gravid uterus, enlarging tumours and obesity are examples of this natural phenomenon.

Surgical attempts at stretching skin to facilitate closure of wounds primarily rely on mobilisation by taking advantage of the skin's inherent extensibility, mechanical creep and stress relaxation. Tissue expanders, presuturing, load cycling with skin hooks and a 'C-clamp' skin-stretching device are examples of methods currently employed to take advantage of these biomechanical properties of skin. Each technique has advantages and limitations to their usage in clinical patients. One common disadvantage of each of these devices, to a variable degree, is their proximity of placement to the surgical site. 'Recruitment' of skin is limited to the immediate vicinity of their application. Additionally, each device requires insertion beneath or into the skin to exert their mechanical effect.

The speaker has designed an externally applied, noninvasive device that applies adjustable tension to skin both locally and distant to the surgical site. The device, termed the 'skin stretcher', enables the surgeon to gradually increase tension on the skin as this tissue progressively accommodates to the load by mechanical creep and stress relaxation.

Skin stretchers (mpavletic@angell.org) are used to mobilise or stretch skin to facilitate wound closure. Uses include:

 Prestretching skin prior to elective surgical procedures (e.g., skin tumour removal).

 Stretching skin during open wound management in preparation for wound closure.

 Application to offset incisional tension postoperatively.

Skin Preparation and Application

Skin preparation includes the following steps prior to skin pad application:

1.  Clip the fur from the sites of skin pad application.

2.  Gently clean the skin with surgical soap and isopropyl alcohol.

3.  The skin must be dry for skin pad application.

4.  Pads generally are placed 10–20 cm from the surgical site. However, multiple skin pads can be placed in a variety of locations, local and distant to the surgery site.

5.  Pads are placed in pairs, on opposing sides of the surgical site.

Skin pads are applied in the following fashion:

1.  Peel off the backing to expose the adhesive surface.

2.  To enhance skin adhesion, apply a few drops of cyanoacrylate adhesive to this contact surface. Spread the glue to a thin uniform layer. Immediately apply the pad to the skin. NOTE: Apply the long axis of the pad perpendicular to the surgical site (long axis of the pad in the direction of stretching).

3.  Manually compress the pad on to the skin for 15–30 seconds.

4.  Apply the remaining skin pads in the same fashion.

After pad application, the elastic cables are attached to the skin pads in the following fashion:

1.  Anchor one end of the cable to one pad.

2.  Stretch the elastic cable across to the paired pad on the opposite site of the surgical site. Apply a mild amount of tension.

3.  Cut the redundant elastic cable from the coil provided.

4.  Repeat steps 1–3 with the remaining pads.

5.  A dressing and bandage may be placed over the surgical site to protect the area from cable irritation.

After application, elastic cables are adjusted in the following fashion:

1.  As the skin stretches and relaxes, the cable tension is increased by uncoupling the cable from one pad. The cable is stretched and reapplied to assure maximum uniform tension is maintained to optimise skin stretching.

2.  Cable tension is adjusted every 6–8 hours.

3.  Depending upon the desired results, skin stretching generally is performed for 1–5 days, depending upon the amount of skin requiring mobilisation. In most cases skin stretchers are used for 72 hours.

Comments

Skin pads can be trimmed with bandage scissors to fit a given area or particular need. In small patients, skin pads can be cut in half and trimmed to conform to smaller donor regions or to offset incisional tension postoperatively. Skin pads also can be slightly bent or 'pre-curved' prior to application to better conform to body contours.

Pads occasionally separate from the skin surface secondary to improper skin preparation, glue application, excessive cable tension or moisture accumulation. The adherent properties of the skin pads also will vary to some degree with the individual patient. Pads can be replaced by the application of additional glue and allowing the supplemental glue to dry for a few minutes before reapplication of the cable. Occasionally, damaged pads will require replacement.

Skin pads are removed by manually peeling them from the skin surface. In so doing, the corneal layer of the skin may be displaced; this outer epithelial layer often reforms within days. Cyanoacrylate glue solvent may be used to facilitate pad removal. Pads retained on the skin surface generally begin to separate spontaneously within a week after application. Skin pads are not reusable.

References

1.  Pavletic MM. An external skin-stretching device for wound closure in dogs and cats. Journal of the American Veterinary Medical Association 2000;217:350–354.

2.  Pavletic MM. Atlas of Small Animal Wound Management and Reconstructive Surgery. 3rd ed. Ames, Iowa: Wiley-Blackwell, 2010.