The flank and elbow folds are situated cranial to the upper hind limb, and caudal to the upper forelimb, respectively. They have two skin layers; an external (or lateral) layer and an internal (or medial) layer. Fat and loose connective tissue is situated between the layers. The function of the skin folds is presumably to enable movement of the limb without undue tension. Vascular supply to the skin folds comes from the subdermal plexus, and also from branches of the lateral thoracic artery (elbow fold) and the deep circumflex iliac artery (flank fold). Each skin fold has attachments to the upper limb and the trunk; the medial layer attaches to the medial skin of the upper limb and the skin of the sternum or inguinal area, respectively, the lateral layer attaches to the lateral skin of the upper limb and the skin of the lateral thorax or flank, respectively.

Because of their multiple attachments, it is possible to mobilise skin folds and move them in a variety of directions whilst preserving their blood supply. Their use has been reported for closing large defects in the pectoral and inguinal locations, the lateral flank and thorax, and the lateral and medial upper limbs. Closure of the 'donor' site is simple, as the resulting medial and lateral incisions may be sutured directly. Unfolding the two layers of the skin fold and rotating or advancing it enable closure of an adjacent wound with little tension.

CLOSURE OF INGUINAL WOUNDS

One or both hind limbs are clipped to the level of the hock, including the lateral thigh. The flank fold is divided from the upper hind limb by cutting the medial and lateral skin attachments whilst leaving enough skin on the medial and lateral thigh to ensure closure of the donor wound with minimal tension. The medial and lateral layers of the skin fold are separated by dissecting through the connective tissue between them, enabling the skin fold to be opened into a U-shaped flap. The skin flap may then be advanced or rotated into the inguinal defect. If the defect is very large, bilateral flank fold flaps may be used. The skin folds maintain a single attachment to the lateral flank.

* Indicates position of the skin at the point of the stifle before and after creation of the skin fold flap

Skin fold divided from its attachments to the upper limb, unfolded and advanced into an inguinal wound

CLOSURE OF PECTORAL WOUNDS

One or both forelimbs are clipped to the level of the carpus, including the lateral upper limb. The medial and lateral attachments of the elbow fold are divided from the upper limb and the skin fold opened out and advanced into the wound. The skin folds maintain a single attachment to the lateral thorax.

CLOSURE OF FLANK WOUNDS

The hind limb on the affected side is clipped to the level of the hock. The attachments of the flank fold are divided from the cranial aspect of the limb and the flap unfolded to enable advancement into a defect on the side of the animal. The skin fold maintains a single attachment ventrally, to the inguinal skin.

CLOSURE OF LATERAL THORACIC WOUNDS

The forelimb on the affected side is clipped to the level of the carpus. The attachments of the flank fold are divided from the caudal aspect of the forelimb and the flap unfolded to enable advancement into a defect on the lateral thorax. The skin fold maintains a single attachment ventrally, to the pectoral skin.

CLOSURE OF WOUNDS ON THE UPPER FORE LIMB

The affected forelimb is clipped to the level of the carpus. Hair is also clipped from the pectoral region and lateral thorax. The elbow fold is mobilised by dividing its attachments to the trunk. The flap is then unfolded to enable advancement into the upper limb defect. The approach is similar for defects of either the medial or lateral aspect of the upper limb. If the flap is used to close a lateral limb defect, it maintains a single attachment to the medial skin layer of the upper limb. If it is used to close a defect of the medial limb, it maintains a single attachment to the skin of the lateral limb.

POSTOPERATIVE MANAGEMENT

Good postoperative care is critical to the success of these procedures. The skin fold is well vascularized and 100% survival can be expected in most cases, as long as the subdermal plexus is not damaged. Drains should be placed at surgery and the wounds protected with a soft, padded bandage. Simple rubber tube drains (penrose drains) may be used, although some surgeons prefer closed-suction drains such as the Jackson-Pratt or others. Pain relief will be required; we usually use incremental doses of morphine (0.1 mg/kg) or buprenorphine (0.01 mg/kg) in dogs. A fentanyl patch, or non-steroidal drugs such as meloxicam may be required if severe pain continues beyond 24 hours after surgery. A broad-spectrum antibiotic such as amoxicillin/clavulanic acid is given for at least 3 days. If the wound has been open for some time and pseudomonas contamination is a possibility, a fluoroquinolone, or gentamicin is given also. Drains are removed between 48 and 72 hours after surgery. The area is bandaged for at least 7 days to reduce dead space, reduce the risk of self-trauma and encourage healing of the skin flap to the subcutaneous tissues. If the bandage is tolerated well, it may be left in place until suture removal.

Assuming that the flaps have been created and employed appropriately, failure of the skin flaps to develop a firm connection with underlying tissues will focus tension on the suture line and is the most common cause of partial wound breakdown after this surgery. Surgeons attempting a skin fold flap for the first time should practice on a piece of cloth or rubber to ensure that they know exactly which skin attachments to divide in order to mobilise the fold in the direction required.

Two layers of sutures are routinely used; a subcutaneous (polydioxanone or polyglactin, interrupted continuous) and skin sutures (polypropylene, single interrupted or cruciate). Sutures are left in for at least 2 weeks and exercise restricted for 3 weeks after surgery.