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Diabetes Watch

A Closer Look At The Digital Fillet Flap For Closing Wounds In Patients With Diabetes

Diabetic foot infections that require surgery can leave large defects where primary wound closure becomes difficult. Secondary wound closure can take months and place the patient at risk for recurrent infection. There is limited data on the incidence of infections in patients with active ulceration but in 2017, researchers suggested an incidence rate of 40 percent in one year.1 Patients who develop foot infections have a risk of amputation that is 154 times greater than those without foot infections.2 That is why rapid wound closure is imperative. 

Active infections and previous infection can leave toes with limited utility. One can then sacrifice a non-functional digit and utilize a digital fillet flap to facilitate wound closure. There is ample evidence to support this technique, even in patients with peripheral vascular disease.3 Using a digital fillet flap is relatively simple to perform and the flap typically has good vascularity.3 

When A 50-Year-Old Male Presents With An Acute Diabetic Foot Infection After Previous Amputations 

A 50-year-old male with diabetic neuropathy presented with an acute infection of a chronic left fourth metatarsal head ulceration. He also had a history of a left fifth metatarsal head infection treated with near complete resection by another surgeon. While the radiographs were unremarkable, advanced imaging revealed findings concerning for osteomyelitis. 

I performed an open fourth ray amputation with debridement for source control of the infection. However, due to the prior fifth metatarsal resection, the patient’s fifth ray was short, making it difficult to close the amputation defect. The patient also had a right leg below-the-knee amputation recently for necrotizing fasciitis so he wanted the left fourth ray amputation site closed as soon as possible. 

After discussion of the risks and benefits, we opted for a staged wound closure via a fifth digit fillet flap. I performed this procedure four days after the fourth ray amputation and confirmation of clear bone margins. The fifth toe was essentially non-functional as there was no articulation with the fifth metatarsal and the fourth ray was previously amputated due to infection. 

Pertinent Pearls In The Surgical Technique For The Digital Fillet Flap 

We ensured supine positioning of the patient and the patient received general anesthesia. I chose to not utilize a tourniquet in order to confirm viable tissue bleeding edges during debridement. I also excised all vascular thrombotic tissues as this appearance reflected the presence of endotoxin release by residual bacteria. After wound debridement was complete, we irrigated the wound with three liters of normal saline via gravity irrigation. 

I proceeded to make a medial midline incision over the fifth toe down to bone to preserve the digital arteries (see first photo above). Once I identified the distal phalanx, I inserted a 0.062 inch K-wire across the toe to keep it stable and minimize skin retraction. I continued subperiosteal dissection until it was possible to fully remove and discard all of the bones of the fifth toe. At this point, it is prudent to flatten out and study the remaining soft tissue envelope to find the best way to cover the wound under minimal tension. If there is still a defect, it is important to direct one’s goals toward ensuring coverage of the weight-bearing side of the wound. 

If possible, three layers of wound closure are ideal. Start with 2-0 Vicryl® (polyglactin 910) pop-off sutures to cover the bone. This requires placing sutures in the deepest part of the wound so I recommend hand tying the sutures after doing so (see second photo above). Next, one closes the subcutaneous layer with 2-0 or 3-0 Vicryl depending on the tissue thickness, starting with the weightbearing surface. 

By working systematically this way, as the flap starts to come together, it will become obvious where one should excise redundant skin. The nail bed skin is usable for closure but excising it is preferable to reduce the risk of contaminating the flap. Skin closure is per surgeon preference. I typically use either 2-0 or 3-0 nylon in a simple or horizontal mattress fashion depending on whether the wound edges require inversion or eversion. 

Postoperatively, I place the patient into a posterior splint or a short-leg cast if patient adherence is an issue. Offloading the flap is possible by applying a layer of temporary padding over the flap and subsequently applying five layers of plaster. Once the plaster hardens, one can remove the temporary padding and apply the short leg cast, using four rolls of fiberglass and covering the toes. I recommend that the patient not bear weight for three weeks. Cast removal takes place at two weeks postoperatively and suture removal is at week three or four (see third photo above). 

Final Thoughts 

The digital fillet flap is a surgical technique that foot and ankle surgeons are uniquely qualified to perform because of their knowledge of biomechanics and familiarity with precise dissection of the toes. This surgery does not require loupe magnification because direct visualization of the artery is not essential for a successful outcome. It does require a level of creativity and intraoperative decision making with regard to deciding where to place tissue and where to excise redundant tissue. There are a variety of situations in which one could use this flap technique, including preservation of length in partial toe amputations to cover a variety of foot wounds and in combination with skin grafting.4-7  

Dr. Chiu is an Associate of the American College of Foot and Ankle Surgeons, and an Assistant Professor in the Department of Orthopaedics and Rehabilitation at the University of New Mexico School of Medicine in Albuquerque, N.M. He is also in private practice in Albuquerque, N.M. 

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By Haywan Chiu, DPM, AACFAS
References

1. Jia L, Parker CN, Parker TJ, et al. Incidence and risk factors for developing infection in patients presenting with uninfected diabetic foot ulcers. PLoS One. 2017; 12(5):e0177916. 

2. Lavery LA, Armstrong DG, Wunderlich RP, et al. Risk factors for foot infections in individuals with diabetes. Diabetes Care. 2006;29(6):1288-1293. 

3. Schade V. Digital fillet flaps: a systematic review. Foot Ankle Spec. 2014; 8(4):273-278. 

4. Baek S, Suh Y, Lee J. Modified toe pulp fillet flap coverage: Better wound healing and satisfactory length preservation. Arch Plast Surg. 2018;45(1):62-68. 

5. Eleizer S, Shai S, Yoav R, Snir H, Steven V, Alon B. Medial forefoot fillet flap for primary closure of transmetatarsal amputation: a series of four cases. The Foot. 2017;33:53- 56. 

6. Schade V. Addressing a gangrenous fifth digit. Podiatry Today. 2011;1(25). Available at: https://www.podiatrytoday.com/ addressing-gangrenous-fifth-digit . Accessed December 3, 2020. 

7. Chung S, Wong K, Cheah A. The lateral lesser toe fillet flap for diabetic foot soft tissue closure: surgical technique and case report. Diabet Foot Ankle. 2014;5:25732. Available at: https://www.ncbi.nlm.nih. gov/pmc/articles/PMC4272413/ . Accessed December 3, 2020. 

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