Interval gangrene following a femoral‐distal bypass for chronic limb threatening ischemia

An 85-year-old man presented with rest pain and dry gangrene to his right foot and calf. Clinical examination showed a femoral pulse but no distal pulses. He had a background of coronary artery disease, atrial fibrillation, hypertension, and moderate vascular dementia. An endovascular procedure was attempted first which showed a long occlusion from the second part of the popliteal artery, tibioperoneal trunk, into the proximal posterior tibial artery (PTA) and peroneal artery (Fig. 1). The PTA was patent to the foot, forming the pedal arch. The anterior tibial artery (ATA) had a short patent proximal segment, but completely occluded distally. Endovascular recanalization of the popliteal artery and the PTA was unsuccessful. He underwent a superficial femoral artery to distal PTA (at the ankle) bypass using ipsilateral reversed great saphenous vein. The procedure was technically successful. Post operatively the necrotic shin wound continued to deteriorate, and his surgical incisions had significant skin and soft tissue die-back (Fig. 2). Over 2 weeks, there was full thickness necrosis of his skin, and the subcutaneously tunnelled vein graft became visible. The foot was well perfused, however the leg was ischemic. Transcutaneous oxygen measurements of his foot were 57 mmHg, whereas on his lower leg where the ischemic changes were, they were a maximum of 23 mmHg. Clinically, the diagnosis was interval gangrene. We achieved limb salvage after extensive wound debridement with graft rerouting and muscle flap coverage, followed by a skin graft (Fig. 2). Interval gangrene is a rare complication after successful peripheral vascular restoration with the term first coined in 1991.1 A commonly agreed upon definition is necrosis in the tissue proximal to a successful distal revascularization procedure, or in other words, necrosis in the 'bypassed segment'.2 After revascularisation procedures, bypassed segments rely on blood from proximal to the anastomosis, via collateral flow or retrograde flow, for perfusion. Interval gangrene may develop when bypassed segments are deprived of good perfusion with inadequate collateral flow due to occlusion of profunda femoris artery or genicular arteries around the knee. Studies have demonstrated the importance of the genicular collateral network, with those with a more patent network having a higher chance of limb salvage.3 The collateral network maybe damaged during surgery leading to interval gangrene. To our knowledge, there have been 12 other reported cases of interval gangrene in literature.4 Ten of these cases are related to bypass surgery with two cases related to femoral artery stenting.4 More than 50% of these cases progressed to a major limb amputation (MLA) within 30 days, reflecting the poor prognosis of interval gangrene.4 Those cases that didn't have an MLA, required extensive wound debridement or in one case, an additional bypass surgery for limb salvage.1, 2, 4-9 In each case the author stated either poor flow from branches coming from the bypassed segment or covered stents preventing flow as the cause of interval gangrene.1, 2, 4-9 These cases are well summarized by Flynn et al.4 Recognition of this condition is vital, as distal bypasses remains as an alternative in cases of endovascular failure. Although alternative procedures cannot completely mitigate the risk, awareness of this complication may decrease further occurrences. The patient's enduring power of attorney has given consent for this report. David Sun: Conceptualization; writing – original draft. Vimalin Vedanayagam: Conceptualization; writing – review and editing. Kevin Tian: Conceptualization; writing – review and editing. Yew Toh Wong: Supervision; writing – review and editing. Victoria White: Conceptualization; supervision; writing – review and editing.