Reconstruction of a Nonhealing Lick Granuloma in a Dog Using a Phalangeal Fillet Technique

Introduction

Canine acral lick dermatitis or lick granuloma is characterized by firm, raised, ulcerative skin plaques resulting from a compulsion to lick; its etiology may be dermatologic or psychogenic.^1–3 Treatment of this condition is complicated, and in selected cases surgical removal of the affected area is indicated, particularly if the lesion is small.¹ Complications resulting from surgical excision include wound dehiscence, owing to excessive skin tension and repeated trauma from a failure to identify and treat the underlying cause of the condition.¹

The reconstruction of distal limb defects in dogs and cats remains a surgical challenge.⁴ Reported techniques include distant direct skin flaps, skin grafts, microvascular-free tissue transfer, and digital pad transposition with phalangeal fillet.^5–14 Many procedures, particularly those involving phalangeal fillet techniques, are used primarily for digital pad defects.^6,10,12–14 A recent report described the transposition of a digital pad to reconstruct a palmer antebrachial defect following excision of an apocrine gland adenocarcinoma in a cat.¹⁵ The aim of this report is to describe the use of a phalangeal fillet technique to reconstruct a nonhealing wound resulting from excision of a lick granuloma on the lateral aspect of the metatarsal region in a dog.

Case Report

A 6.5-year-old, castrated male Dalmatian was presented to The Queen’s Veterinary School Hospital, University of Cambridge, with a history of a nonhealing wound located on the right foot over the lateral aspect of the fifth metatarsal bone. Three months previously, a lick granuloma lesion was excised from this region by the referring veterinarian, but the primary wound closure had dehisced. Despite attempts at open wound management and surgical debridement, the wound did not heal.

At presentation, a 3 cm-diameter bed of exuberant chronic granulation tissue was present, with the surface covered by purulent exudate [Figure 1]. Dermatological examination failed to reveal any other cutaneous lesions, and radiographs of the metatarsal area demonstrated only a mild periosteal reaction on the lateral fifth metatarsal bone. Under general anesthesia, the wound was excised en bloc, and the tissue was submitted for histopathology and bacterial and fungal culture. Open wound management with daily lavage and wet-to-dry dressings was commenced in preparation for skin grafting. Histopathological analysis revealed bacterial pyoderma with a neutrophilic infiltrate (as well as ulceration, granulation, and fibrosis), with no evidence of underlying neoplasia [Figure 2]. Fungal cultures were negative, but bacterial cultures grew Staphylococcus aureus that was resistant to all antimicrobials tested except cotrimoxazole and oxytetracycline. Parenteral treatment was started with trimethoprim/sulphonamide^a (20 mg/kg per os [PO] q 12 hours) and clomipramine^b (1 mg/kg PO q 12 hours). Clomipramine was given in an attempt to address the suspected psychogenic cause of the original lesion.¹

Following 3 weeks of medical treatment and open wound management, the area was skin grafted. The dog was pre-medicated with methadone^c (0.3 mg/kg intramuscularly [IM]) and acepromazine^d (0.03 mg/kg IM) and induced with propofol^e (6 mg/kg intravenously in incremental doses). The skin graft was full-thickness and meshed and was harvested from the right lateral thoracic region.⁹ After application of the graft, the limb was placed in a Robert Jones bandage, and the graft was examined every 48 hours. Ten days postoperatively it became apparent that the graft was not viable, and further surgical debridement of the wound was performed. A second bacterial culture from the wound was negative and revealed no further growth of the resistant Staphylococcus aureus. Because of graft failure and the inability of the wound to heal by secondary intention, a phalangeal fillet technique was performed to provide a local, axial pattern flap for reconstruction of the wound.

Anesthesia was induced as described previously, with the addition of morphine^f (0.3 mg) administered epidurally. An incision was made around the margins of the wound, continuing distally along the plantar-lateral aspect of the fifth digit. The incision extended circumferentially around the distal phalanx and the associated pad. After careful identification and retraction of the neurovascular bundles on the plantar aspect of the foot, the proximal, middle, and distal phalanges were removed [Figure 3]. The fifth digital pad was carefully excised as close to the pad as possible to avoid vascular trauma. Hemostasis was achieved using a combination of bipolar cautery^g and digital pressure. The resulting skin flap was then elevated and rotated 180° to lie directly over the defect. Closure was achieved using 4-0 polyglecaprone^h in a simple interrupted pattern for the subcutaneous tissue and using 3-0 nylonⁱ for the skin in a simple interrupted pattern. A closed-suction drain constructed from a perforated 19-gauge butterfly catheter attached to a 5-mL vacutainer tube was inserted into the wound prior to closure [Figure 4].

The wound was supported with a soft bandage that was changed daily for 5 days. The drain was removed 48 hours following surgery. Three days postoperatively, partial separation of the most proximal aspect of the flap occurred, which was treated with minimum debridement of the skin edges and the addition of several more skin sutures. At suture removal 15 days after surgery, the wound had completely healed and the dog was fully weight-bearing on the limb [Figure 5]. A follow-up telephone call with the owner 4 months postoperatively indicated good functional results. The dog did attempt to lick the healed wound for a short time once the bandage was removed, but the itch-lick cycle was broken by the use of distraction techniques and a change in environment (the owner remained at home with the dog). Clomipramine administration was stopped after 2 months.

Discussion

The phalangeal fillet technique has been primarily used in conjunction with digital pad transfer for reconstruction of the major weight-bearing surfaces of the paws of dogs.^7,10,12–14 This technique has also been described as a method of covering soft-tissue defects of the digits and dorsal paw following skin trauma, with or without osseous damage.⁹ In humans, this technique provides coverage superior to that of skin grafts or distant flaps to the hand, and it allows excellent function and sensibility to be maintained. ^16,17 This surgery is considered so successful in humans that an extended version has been developed for defects up to the metacarpophalangeal area.¹⁷ This modification is comparable to the surgery that was performed on the dog reported here, where a defect overlying the metatarsal region was completely covered using a phalangeal fillet. A similar technique has recently been reported in the cat, although the digital pad was included in the transfer of skin over a defect in the palmar carpal area.¹⁵ Because the wound in the case reported here was overlying a nonweight-bearing surface of the foot, it was not considered necessary for the pad to be included in the transfer.

The advantage of this phalangeal fillet technique over other reported methods of distal extremity reconstruction (i.e., skin grafting, distant direct flaps, tubed pedicle flaps, microvascular tissue transfer) is that a local axial pattern flap is created that allows simple transfer of skin with a consistent vascular supply into an adjacent defect.¹⁵ In this case a skin graft was attempted first, but it failed, possibly as a result of an inadequately vascularized recipient granulation bed. The subsequent flap that was created was based on a vascular pedicle consisting of the fourth plantar common digital artery (arising from the deep plantar fourth metatarsal artery) and the fourth superficial dorsal metatarsal vein.⁵ A previous study on microneurovascular free digital pad transfer in the dog established that the blood supply to the fifth digit of the rear foot was consistent and easily accessible.¹⁰ Because the fifth digit is not a major weight-bearing digit, the skin in this region can be used safely as a donor site, with minimal functional compromise.

The long-term prognosis in this case relied on treatment and resolution of the underlying condition. Clomipramine has been effective for the treatment of canine acral lick dermatitis; however, it was unclear whether the relatively short-term therapy with this drug alleviated the underlying condition in this dog.¹⁸ The successful treatment of lick granulomas relies on a thorough investigation of potential underlying causes (which was not possible in this case because of owner noncompliance) and a combination of treatments that may include systemic, topical, behavioral, and surgical methods.¹

Conclusion

Surgical excision of an acral lick granuloma resulted in a chronic, nonhealing wound in a 6.5-year-old Dalmatian. The wound failed to heal by secondary intention and following a full-thickness skin graft. A phalangeal fillet technique using skin from the lateral aspect of the fifth metatarsal area, but not including the digital pad, was used to successfully reconstruct the defect.

Acknowledgments

The authors thank Sean Haugland and Jacki House for their assistance in the analysis of the histopathology and production of the photomicrograph image.