Reverse Saphenous Conduit Flap in 19 Dogs and 1 Cat
ABSTRACT
The purpose of this retrospective study was to report the outcomes of 19 dogs and 1 cat undergoing reverse saphenous conduit flap between 1999 and 2016. Reverse saphenous conduit flap was used to treat traumatic wounds and wounds resulting from tumor excision in the hind limb; the majority of cases had medial shearing injuries. All animals had complete flap survival. In five animals (20%), minor donor site dehiscence occurred, which did not require surgery. Other postoperative complications included signs of severe venous congestion in one dog. Reverse saphenous conduit flap is a useful technique to repair skin defects of the distal hind limb.
Introduction
Large skin defects in the distal hind limb are a challenging problem. Defects at or below the tarsus are often unsuitable for primary or secondary closure; other options include second-intention healing, releasing incisions, skin flaps, free skin grafts, tissue expansion, and microvascular free tissue transfer.1,2 Second-intention healing is often used, but disadvantages include a fragile epithelial surface, prolonged healing time and wound care, and wound contracture.3 Free skin grafts are versatile, technically simple to perform, and can result in normal-haired skin with a good cosmetic outcome (depending on the type of graft). However, free skin grafts require well-vascularized recipient beds and are exquisitely sensitive to excessive motion, infection, or fluid accumulation under the graft.4,5
The reverse saphenous conduit flap (RSCF), a variation of the axial pattern skin flap technique, offers a unique solution for reconstruction of soft-tissue defects over the tarsus and metatarsus.6,7 The flap takes advantage of a vascular conduit that gives rise to several direct cutaneous arteries that supply the skin of the hind limb. The relevant vascular anatomy is well described in angiographic studies in dogs and cats.7,8 Despite its potential to provide a practical solution to a common problem, only a scant amount of information regarding the clinical use of RSCF in veterinary patients has been published.9–11 The purpose of this retrospective study was to report the outcome (success rate and complications) of RSCF in 19 dogs and 1 cat. We hypothesized that RSCF would be useful for treatment of extremity hind limb wounds with minimal complications.
Materials and Methods
Dogs and cats who underwent RSCF at Virginia-Maryland College of Veterinary Medicine from 1999 to 2016 were identified, and medical records were reviewed. Data retrieved included signalment, body weight, the location and the cause of the wound, time from injury to surgery, duration of postoperative hospitalization, surgical complications, and patient outcome.
Preoperative Management
Traumatic wounds were managed until they were macroscopically free of infection or necrosis. Before the decision was made to perform RSCF, patients with traumatic wounds had vascular integrity partially assessed by placing a Doppler probe over the dorsal tarsus/metatarsal area to ensure that a clear pulse could be detected from the dorsal pedal artery. Patients whose wounds were created by tumor excision had RSCF performed immediately after tumor excision.
Surgical Procedure
Intraoperative antibiotics (cefazolina 22 mg/kg IV q 2 hr) were used in all cases. Patients were placed in lateral recumbency with the affected leg down and the opposite leg abducted. The flap was outlined on the medial aspect of the leg (Figure 1A). The proximal incision was made at the level of the mid to proximal thigh, and dissection was continued down to the femoral vasculature to identify the origin of the saphenous artery before continuing further. The saphenous artery and the medial saphenous vein were identified, ligated, and transected at their origin from the femoral artery and vein. The cranial and caudal borders of the flap extended distally from the proximal incision, converging as they went distally with care to remain approximately 0.5–1 cm cranial and caudal to the cranial and caudal branches of the medial saphenous vessels, respectively. Flap width was determined by the size of the wound and the location of the medial saphenous vessels and was limited by the surgeon’s assessment of what would allow for donor site closure. Flap length (and ultimately the location of the base of the flap) was determined by the location of the wound—the flap was extended only as long as necessary to cover the wound without tension. During flap elevation, dissection proceeded at a depth that ensured patency of the medial saphenous vessels. This required dissection deep to the gastrocnemius fascia to avoid damage to the caudal branch of the saphenous artery and medial saphenous vein (Figure 1B).
Citation: Journal of the American Animal Hospital Association 54, 4; 10.5326/JAAHA-MS-6716
A bridging incision was made between the donor site and the recipient bed. The flap was rotated toward the skin defect and sutured to the wound edges in an interrupted pattern using 3-0 or 4-0 monofilament nonabsorbable suture (polypropylene or nylon) or skin staples. The donor site was closed in two layers, using 3-0 monofilament absorbable suture (polydioxanone) in the subcutaneous tissue with an interrupted pattern followed by 3-0 or 4-0 monofilament nonabsorbable suture or skin staples in the skin with an interrupted pattern. A drain was not placed under the flap.
Aftercare
A light full-limb bandage was placed after the surgical procedures in all animals. When indicated, a medial splint was incorporated into the bandage to immobilize the tarsus. Bandages were maintained for various durations according to the cause of the injury (other healing wounds on the same limb, medial tarsus instability); minimum bandage duration was 1 day after surgery. Butorphanolb (0.4 mg/kg IV), morphinec (0.1–0.5 mg/kg subcutaneous), or hydromorphoned (0.05–0.1 mg/kg IV) was administered every 4–6 hr for analgesia during the first 24–48 hr after surgery at the discretion of the supervising clinician. Carprofene (2.2 mg/kg per os [PO] q 12 hr) and codeinef (2 mg/kg PO q 8 hr) or butorphanolb (0.4 mg/kg PO q 6 hr) were administered for 5–7 days after surgery. Cephalexing (22 mg/kg PO q 12 hr) was administered for 2 wk after surgery.
Outcome Assessment
Outcome evaluation was by clinical examination during postoperative hospitalization and at each recheck. Surgery sites were monitored until complete healing occurred. Clinical examination included visual assessment of the flap and donor site (color, edema, congestion, seroma formation, necrosis, and dehiscence). Long-term follow-up was by means of telephone interviews with clients and referring veterinarians. They were asked about the cosmetic results of the flaps and donor sites and regrowth of tumor if applicable.
Complications were defined as those affecting the RSCF or donor site within the postoperative period (early < 14 days, late > 14 days) and as major or minor. Major complications were defined as any complication necessitating a second surgical procedure. Minor complications were self-limiting or medically managed. Mild flap edema and erythema in the early postoperative period were considered normal for RSCF and were not classified as complications. The overall incidence, severity, and time of occurrence of complications were recorded.
Results
Study Population
Nineteen dogs and one cat underwent RSCF. Five patients had previously been included in an unrelated retrospective study.12 There were nine spayed females, two intact females, and nine neutered males. Age ranged from 10 mo to 14 yr (median, 5 yr). Median body weight was 17.5 kg (range, 4.2–43.4 kg). Ten dogs were mixed-breed, two were Labradors, and the remaining seven included one of each of the following breeds: German shepherd dog, beagle, Australian shepherd, chow chow, Shetland sheepdog, Jack Russell terrier, and Great Pyrenees. The cat was an American domestic shorthair.
Wounds
All 20 animals (19 dogs and 1 cat) had distal hind limb wounds with varying degrees of associated musculoskeletal damage: 17 tarsal wounds (15 medial, 1 lateral, and 1 dorsal aspects), 1 metatarsal, 1 calcaneal, and 1 caudal crus. The causes of the wounds were shearing injury (n = 14), snake bite (n = 1), dog bite (n = 1), foreign body (n = 1), bandage sore (n = 1), and tumor resection (n = 3 [2 dogs and 1 cat]; Table 1).
In five dogs, negative-pressure wound therapy was used during wound treatment. Time from wounding to surgery ranged from 0 days (patients with tumor excision) to 14 days.
Surgical Procedures
The 20 surgeries were performed by two board-certified surgeons or residents who were directly supervised by those surgeons. No intraoperative complications were noted. In patient 3, the RSCF did not extend over the most distal portion of the wound. The remaining wound was managed as an open wound for several days before eventually being covered with a mesh skin graft during a subsequent procedure. Patient 18 received a mesh skin graft to a small defect on the cranial aspect of the tarsus at the same time the RSCF was applied to a wound over the calcaneus. In patient 20, the distal half of the caudal belly of the sartorius muscle was elevated with the RSCF to create bulk and fill dead space in a deep wound of the caudal crus. In this dog, a Jackson-Pratt drain was placed in the donor site and exited through a skin incision over the craniolateral thigh. Two dogs received a type II external skeletal fixator at the time of surgery, and three dogs received a medial splint to immobilize the tarsus to treat medial collateral instability.
Outcome
The median hospitalization time (surgery to discharge) was 5.5 days (range, 1–11 days). There were no major complications. Six dogs (30%) had minor complications in the early postoperative period. Five dogs had partial donor site dehiscence. Dehiscence sites comprised less than half the length of the donor site closure incision and were located at the level of the stifle (four dogs) or just distal to the stifle (one dog). All were treated without surgery, and the dehiscent areas healed by second intention. All animals exhibited signs of mild venous congestion including edema and erythema in the early postoperative period (Figure 2). Patient 20 exhibited signs of flap congestion including severe edema, purple discoloration of the flap, and serous exudate through the skin of the flap on the day after surgery. This patient also exhibited distal limb edema for 7 days after surgery. A bandage incorporating negative-pressure wound therapy was placed over the flap and maintained from days 1 through 6. On day 7, the flap’s color had improved, and the effusion and edema had resolved. In all patients, flaps healed entirely without necrosis or dehiscence.
Citation: Journal of the American Animal Hospital Association 54, 4; 10.5326/JAAHA-MS-6716
Patients were followed up for 12 mo (range 7–31 mo). No late postoperative complications were noted. Clients and referring veterinarians reported acceptable cosmetic outcome in all patients. Minor abnormalities in the hair coat included the different direction and color of the hair and a relatively thin hair coat on the tip of the flap (which had come from the proximal medial thigh) relative to the surrounding skin in long-haired patients.
Tumors resected included grade II mast cell tumor (dogs 16 and 19) and low-grade fibrosarcoma (cat). Patient 16 (grade II mast cell tumor) had complete tumor excision with no evidence of regrowth after 1 year. In two patients (the cat and dog 19), the tumors were incompletely resected. The cat (low-grade fibrosarcoma) had an incomplete deep margin and regrowth of tumor 8 and 22 mo after reconstruction; lumpectomies were performed by elevating the skin of the healed RSCF and marginally excising the new tumor before replacing the skin flap. Nine mo after the second lumpectomy, the affected limb was amputated due to regrowth of tumor. In patient 19 (grade II mast cell tumor), the neoplastic cells extended to the deep and lateral surgical margins; after 7 mo, no evidence of regrowth has been noted.
Discussion
The results of this retrospective study support our impression that RSCF is a robust method to reconstruct defects of the distal hind limb with good outcome and low complication rates. In this series, which is the largest clinical case series published to date, we observed a 100% flap survival rate.
Although it is often classified as an axial pattern flap, the RSCF is fundamentally different from other axial pattern flaps—this difference has implications for correct technique and expected appearance following surgery. Unlike conventional axial pattern flaps, which are based on a direct cutaneous artery, the RSCF relies on a deep vascular conduit, which in turn gives rise to multiple direct cutaneous arteries that supply the skin of the hind limb. Indeed, a small axial pattern flap has been described around one of the individual direct cutaneous arteries arising from this conduit.13 The deep vascular conduit can be imagined as “U,” with the proximal end of one arm representing the saphenous artery and medial saphenous vein and the proximal end of the other arm representing the cranial tibial artery and vein (ultimately a distal continuation of the femoral artery and vein). Because of vascular branching, the distal loop of the “U” consists of multiple anastomotic connections, ranging in location from just proximal to the cranial tarsus (anastomosis of the superficial branch of the cranial tibial artery to the cranial branch of the saphenous artery) to within the metatarsal area (anastomosis of the dorsal pedal artery to the plantar arteries via the perforating metatarsal artery) and potentially beyond. Once the saphenous artery and medial saphenous vein are ligated at the beginning of flap development, blood flow through the conduit depends on these distal vascular connections.
The saphenous artery and medial saphenous vein branch into cranial and caudal branches within the boundaries of the flap. Distal anastomoses to both branches are integral to maintaining blood flow (especially venous drainage) to the vascular conduit as a whole. It has been demonstrated that the integrity of both the cranial and caudal branches must be maintained for reliable RSCF survival.14 In our experience, it is easy to inadvertently damage one of these branches, either during flap elevation or when creating a bridging incision to lay down the flap. As dissection moves distally during flap elevation, one must include gastrocnemius muscle fascia to preserve the caudal branch of the saphenous artery and medial saphenous vein.7 Thus, the RSCF has been referred to as a fasciocutaneous flap by some authors.
In its original description, the proximal border of the flap is described as “across the central third of the inner thigh, at or slightly above the level of the patella,” and in the illustration of the technique, which is commonly reproduced, the proximal border appears to be at the level of the patella.2,7 We have found that identifying the origin of the saphenous artery and medial saphenous vein where they arise from the femoral artery and vein helps the surgeon to ensure that dissection progresses deep to the vascular conduit. We were able to do this more easily by making the initial incision in the mid to proximal thigh (closer to the body wall than to the patella). The skin at this proximal level is well supplied by cutaneous arteries arising from the vascular conduit, and we did not observe necrosis of skin that came from the proximal medial thigh.15 Our practice was to initiate elevation of the flap at this more proximal level and to extend dissection distally only as much as needed to cover the intended defect, such that the location of the “base” of the flap was variable, whereas the “distal edge” of the flap (which originated from the proximal thigh incision) was constant. This is in contrast to conventional axial pattern flaps in which the base remains constant and the distal edge goes only as far as is needed for each individual case.
Many of the cases reported here were treated for medial shearing injuries. In trauma cases such as these it is important to ensure viability of the vascular conduit before choosing RSCF. All trauma cases in this report had their vascular supply examined by placing a Doppler probe over the dorsal aspect of the tarsus to ensure a clear pulse from the dorsal pedal artery. This technique only evaluates one branch of the vascular conduit. Angiography may give a more global evaluation of vascular integrity and has been recommended in trauma cases prior to RSCF.7
The medial saphenous artery also supplies the distal half of the caudal belly of the sartorius muscle.15 The surgeon can take advantage of this fact and include sartorius muscle with the flap, creating a myocutaneous flap, as was done in one case in this report. A myocutaneous free flap based on the medial saphenous vessels and incorporating the caudal belly of the sartorius muscle was used successfully in three dogs in a previous report.6
In the study reported here, all animals had a good outcome, with no minor and self-limiting complications. Five dogs in this study (20% of patients) developed donor site dehiscence. This complication has been commented on by other authors who observed donor site dehiscence rates ranging from 12.5–20% in flaps with similar boundaries.6,14,15 In another clinical case series that reported six cases of RSCF, this complication was not mentioned.9 This complication may be more of a concern with the RSCF compared with other axial pattern flaps because there is limited skin available at the donor site relative to the flap width. In this case series, all donor site dehiscence areas were located at the medial stifle or just distal to stifle. This is typically an area of high tension during closure and is presumably an area that is challenged by more motion after surgery. The experience of donor site dehiscence led us to plan flaps that narrowed as they approached the base; however, one is still limited by the minimum flap width, which is dictated by the two major branches of the medial saphenous vessels. Tension-relieving techniques such as releasing incisions or stifle immobilization using external fixation or splinting may have prevented donor-site dehiscence in these cases.
In our experience, signs of mild venous congestion (mild edema and erythema) are expected within the first wk of surgery after the RSCF procedure. This has been previously noted and is attributed to the fact that as blood flow reverses within the vascular conduit, valves within the veins cause partial occlusion to venous blood flow.7 One of the cases in this series (patient 20) suffered severe edema, purple discoloration, and serous effusion from the flap, indicating severe venous congestion. This was attributed to venous vascular compromise from the trauma that went undetected before surgery (this case had suffered multiple bite wounds to the pelvic limb). This was also the only patient in which a portion of the sartorius muscle was included into the flap—although the muscle may have contributed to the venous congestion, free microvascular transfer of a similar myocutaneous flap incorporating the sartorius muscle has been reported in three cases without severe venous congestion after surgery.6 In patient 20, because the effusion was so profuse that it quickly saturated a normal bandage, a bandage incorporating negative-pressure wound therapy was used as a method to remove fluid and prevent skin maceration and the need for frequent bandage changes. Leeches have been used to treat severe venous congestion in skin flaps in previous reports.6,11
Several other techniques have been used to successfully reconstruct large distal extremity wounds in dogs and cats, including distant pedicle flaps, tubed flaps, tissue expansion, microvascular free tissue transfer, free skin grafts, and second-intention healing.6,16–22 Free skin grafts have received recent attention in the veterinary literature, and several case series have documented their successful use over distal extremity wounds.19–21 Although traditionally used once a granulation tissue bed has formed, free skin grafts can take on healthy muscle, fascia, paratenon, and periosteum and therefore can be used to immediately cover distal extremity defects in a single-stage procedure after tumor removal.19 However, their use is not recommended over denuded bone, irradiated tissue, avascular fat, or chronic granulation tissue such as over chronic ulcers; in these cases, skin flaps may be the better choice.23 Free skin grafts vary widely in their reported success rates, with a recent large clinical study reporting a higher success rate in cats (77%) than in dogs (38%).21 The use of negative-pressure wound therapy in the immediate postoperative period may improve free graft survival and was associated with 100% success in seven dogs.20 Axial pattern skin flaps also vary in reported success rates; although individual case reports often show complete success, a retrospective review of 73 axial pattern flaps (including 10 cases who received RSCF) revealed an overall high complication rate (89%) but noted that complications were usually minor and did not require second surgery.10,24,25 We report excellent (100%) flap survival after RSCF in this case series; however, the retrospective design of this study precludes outcome comparison with other techniques such as free skin grafts.
Limitations of this study are inherent to its retrospective design. Details such as flap dimensions were not consistently recorded in the medical record, resulting in some loss of information. Details about complications, especially minor complications, were dependent on their being recorded in the medical records and therefore may be incomplete in some cases.
Conclusion
The reverse saphenous conduit flap is a robust technique that is useful to repair wounds of the distal hind limb. With knowledge of the vascular anatomy in the area, this technique results in reliable flap survival. Partial donor site dehiscence is common but did not require a second surgery in the patients of this report.
(A) Outline of the planned reverse saphenous conduit flap on the medial aspect of the femorotibial region. Patella indicated by the arrow. (B) Intraoperative view of the raised flap. *, femoral vessels; G, gastrocnemius muscle; Gr, gracilis muscle; M, medial saphenous vein; S, caudal head of sartorius muscle.
Appearance of the flap 24 hr after surgery. Mild flap erythema and edema is evident.
Contributor Notes
J.V.J. Cavalcanti’s present affiliation is the Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, Florida.
