Fillet flaps are frequently raised as part of the spare part concept4 in the reconstruction of weight bearing areas of the foot. It is an axial pattern flap harvested from non-functioning or unsalvageable digits. Described in 1965 by Snyder and Edgerton5, filleted islanded neurovascular flaps from the toes and anterior sole were used to resurface neuropathic heel ulcers. Similarly, Kaplan described the use of a filleted big toe flap to cover anterior sole defects in 19696.
In a formal ray amputation, the metatarsal head is removed with the digit and the joint capsule of the MTPJ is excised as an exposed capsule impedes granulation of the wound. We apply topical negative pressure wound therapy (TNPWT) to ray amputation wounds to accelerate granulation and healing. However, a substantial proportion of patients have closely-packed metatarsal heads hence the combination of capsule excision with TNPWT on the wound bed results in the gradual exposure of the adjacent joint capsule, with eventual deterioration of the toe necessitating another ray amputation. This can be avoided in the use of the TOPHAT filleted toe flap technique whilst allowing the wound bed to benefit from the granulation promoted by NPWTi-d instillation therapy. We employ the use of a toe fillet flap derived from the non-salvageable sacrificed adjacent toe to protect the same MTPJ. We have shown good results with patients in our series.
The vascular supply of the toe fillet flap has historically been thought to be less reliable compared to that of the finger fillet flap7. Coupled with the fears of inadequate perfusion from underlying peripheral vascular disease that most of such patients have, the use of loco-regional flaps in reconstructing post-ray amputation wounds has been largely replaced by TNPWT and eventual skin grafting8, or more commonly, leaving the wound to heal by secondary intention. However, secondary wound healing has disadvantages such as a prolonged time of healing in large plantar cavity wounds while continuously exposing the patient to recurrent infection and risks inherent with prolonged off-loading9. Frequent dressing changes in this instance also impose high costs and inconvenience to the patient.
The selection criteria for employing fillet toe flaps were developed by Nather and Wong10 but are over-stringent and exclude patients with significant peripheral arterial disease (one or two palpable pedal pulses, ankle brachial index (ABI) ≥ 0.8 and toe brachial index ≥ 0.7) who form the bulk of these patients. In 2014, Chung et al11 presented the use of a toe fillet flap for the coverage of the MTPJ adjacent to the ray amputation wound that had been exposed after the initial debridement. However, their patients were as per Nather and Wong’s criteria10. In a similar fashion, others such as Aerden et al also selected for patients with no or mild peripheral vascular disease prior to attempting their filleted toe flaps9. The majority of patients in our series have severe peripheral vascular disease (critical limb ischemia) and most required endovascular intervention. Yet we were still able to perform the TOPHAT filleted toe flap technique with minimal complications and flap survival rates which we deemed exceptional in this cohort (of vascular surgical patients). The fillet toe flap is a reliable flap for wound coverage despite microangiopathic disease of the plantar digital arteries12 and helps decrease the overall wound burden without additional donor site morbidity. We believe that such strict selection criteria are not necessary for selecting for the fillet toe flap because in doing so we will exclude patients who may benefit from it.
With proper wound debridement and subsequent application of NPWTi-d therapy, the wound healing trajectory shifts from delaying wound infection to granulation formation. Even with poorer patient demographics with significant underlying peripheral vascular disease, the mean time to the wound bed being ready for final skin coverage with skin grafting was 49.5 days and the complete wound healing of the entire wound bed in our series was 107.5 days. Other case reports for foot wounds closed entirely with a fillet flap alone reported a healing time of 9-months to 1 year9,11,12. Chung et al described a lateral lesser toe fillet flap for the diabetic similar to toe filleting technique with a similar intention to reduce the overall wound burden without the concurrent use of a TNPWT. However, the time taken for complete wound healing in their case report took 6-months11. Even with patients with severe arterial disease requiring endovascular intervention, our time to complete wound healing was shorter. We believe that a combination technique using the filleted toe flap and careful “barrier and buttress” NPWTi-d dressing helps accelerate the granulation process and allow for earlier skin grafting and more rapid wound resolution.
The TOPHAT filleted toe flap technique in the management of post ray amputation wounds is a simple and reproducible method that does not require complex microsurgical skills or techniques. The vascular supply is consistent based on the digital arteries of the toes, even in patients with diabetes and peripheral vascular disease13,14. Hence it is useful in patients where microsurgery may be difficult and reduces the need for more complex soft tissue reconstructive procedures15,16. More studies are warranted to better select patients for the procedure without excluding the cohort of vasculopaths – doppler studies of the digital arteries in the toes designated for amputation may prove useful.