Split Thickness Flap - Indications, Contraindications, and Treatment

Introduction

Grafting of the skin is a surgical procedure that is done by transferring a part of the skin from one area of the body to another. This process is used most of the time to cover a large surface area of wounds. The concept of this procedure is the extraction of the skin from a parent or donor site that is capable of healing over time, enabling the tissue to be transferred. Grafts in general can be of two types namely the split thickness graft and full thickness graft, where the split-thickness graft is a portion of the graft that is extracted from the donor site, which contains the epidermal layer along with part of the dermis layer. The skin graft, unlike the flap does not have its supply of blood but rather they depend on the vascularization of the wound site it is going to be placed on.

Split thickness grafts can be used from various sources like allograft, autograft, homograft, and xenograft. Several anatomical sites have been used to register The anatomical sites from which the grafts are extracted are commonly the trunk and lateral thigh. It is also a preferred option that the grafts are extracted from areas that are not in esthetical concern. The thickness of the graft can be classified according to the thickness ranging from 0.15 to 0.3mm in the case of a thin graft, 0.3 to 0.45mm in the case of an intermediate graft, and 0.45 to 0.6mm in the case of a thick graft.

What Is the Anatomy of STSG Graft?

The anatomy of the split-thickness graft consists of two portions, namely the dermis and epidermis. The epidermal layer of the skin consists of the outermost layer of the skin which is made up of keratin-forming cells. The epidermis is a thin layer of skin that is semi-transparent, and mainly functions as a skin barrier. The epidermal layer also constitutes cells like melanocytes, Langerhans, and Merkel along with a few nerve endings. The epidermal layer also consists of structures like hair follicles, sebaceous and sweat glands that act as derivative layers which invaginate with the dermal layer of the skin. Whereas the dermis is a very fibrous skin layer that lies beneath the epidermal layer and is composed of cells like collagen, elastin, and glycosaminoglycans. The upper portion of the dermal layer also consists of the papillary structures, a group of nerves, and blood vessels.

What Are the Factors to Be Considered While Harvesting an STSG?

Before harvesting a flap it is important to consider its prerequisites, to know the quality, quantity, and longevity of the flap, and these factors to be considered are:

• The Thickness of the Grafts - The preferable thickness of the flap is neither very thick nor very thin but should have an ample amount of thickness to maintain the structural integrity and well as to allow the perfusion of blood.

• Contracting Ability - The graft should have a minimal shrinkage ability as the wound can appear distorted and a size reduction at the site of placement of the graft.

• Vitality Rate of the Donor Site - When harvesting a new layer of graft, part of the dermal layer as well as hair follicles are retained, which helps in adhering the graft to the donor area and trying to extract the vitality of the skin through the donor site making it viable.

• Matching Esthetically - The main purpose of restoration of the defective area is to establish the esthetic nature of the graft. Hence, it is important to see if the graft and the donor site match each other esthetically.

• Durability - The durability of the flap indicates the elastic nature of the flap and the strength that is provided to the wounded area by graft placement. So it is crucial to consider these factors for a long and successful event.

How Is Graft Placement Done Surgically?

First and foremost it is very crucial to gain the trust and the consent of the patient, so considering it both as a plastic correction as well as graft extraction, the patient should be well aware of the treatment scenario, procedures to be done, and follow-up care. All these must be informed to the patient before beginning the procedure. This is followed by preparing the site to receive the graft being the wound bed as a clean surface area makes the wound bed more susceptible to receiving the graft. Various techniques are employed in debriding the wound surface, the most commonly used one is by using a scalpel, dermatome, hydrological devices, and Norsen debrider. The debirementation of the wound should be in such a way that the edges and base of the

How Do the Grafts Accommodate the New Area?

Once the graft is placed in the recipient site, the tissue accommodates itself through the following process. The steps of adhesion are:

• Imbibition: The STSG graft slowly starts to absorb nutrients and oxygen from the site of the wound over which it is placed. During the initial phase, the skin graft appears very pale and ischemic and slowly and gradually starts to absorb the nutrients, reestablishing the vasculature of the graft. During this process, the flap appears white or paler when observed.

• Inosculation: This is the time when the flap slowly starts changing its color from pale to pinkish, indicating the establishment of the vasculature. This network of vasculature from the cut wound to the lower surface of the graft is established at the wound site. The process of inosculation takes place within forty-eight hours of graft placement.

• Revascularization: This process of revascularization is provided from the recipient site to the donor site by the process of ingrowth of endothelial cells slowly proliferating into the basal lamina.

What Are the Indications of Split Thickness Graft?

The STSG graft is indicated in conditions like:

• Chronic skin loss.

• Traumatic wound.

• Ulcers.

• Burn.

• Acute skin loss conditions.

• To cover the exposed muscle.

What Are the Contra-Indications of Split Thickness Graft?

The STSG graft is contraindicated in conditions like:

• Wound - in case of the site of pre-existing wound.

• The nerves showing vessel damage.

• Cancers.

• Active bleeding.

• Chronic steroid usage.

Conclusion

The main purpose of the STSG graft is to achieve a successful outcome. Although a vast number of factors can jeopardize the outcome of the surgery. Care should also be taken in selecting the donor site, the type and area of the wound, followed up by skin grafts, and extreme post-operative care shows great beneficial results. Although the surface area needs functional rehabilitation through exercises post-healing, the success rates are still commendable and mostly preferred treatment of choice.