Diabetic foot: the window to avoid amputation is narrower than you think糖尿病足：避免截肢的窗口比想象中更窄

The sequence that leads to amputation

A patient notices a blister or a small wound on the sole. It is dressed at home for two weeks. It becomes deeper and smells. Antibiotics are started. Three weeks later the toe is black, and someone says the word "amputation" — usually about the toe, then about the ray, then below the knee.

Every step in that sequence was a decision, and at least three of them were avoidable. The single most consequential one is the first: nobody checked the blood supply.

Perfusion comes before everything

A wound cannot heal in tissue that is not being perfused, and antibiotics cannot reach it. Before any plan, you need:

• Palpable pulses, or an absent pulse that is taken seriously
• Ankle-brachial index — remembering that it is falsely elevated in calcified vessels, common in diabetes
• Toe pressure or transcutaneous oxygen if the ABI is unreliable
• Duplex ultrasound, and CT angiography if a revascularisation is being considered

If the foot is ischaemic, the order is: restore inflow, then debride, then cover. Doing it the other way around converts a salvageable foot into a major amputation.

What microsurgery adds

Once inflow is restored and infection is controlled, the remaining problem is a hole: tendon, bone or joint exposed where skin should be. Skin grafts will not take on bare tendon or bone. That is where a free flap — tissue moved with its own artery and vein from the thigh, back or forearm — closes a defect that would otherwise be a amputation.

The numbers that matter are not the flap survival rate alone but limb salvage at one year and independent walking at one year. Ask for those, not for a general success figure.

The signs the window has closed

Honesty matters more here than optimism:

• Extensive dry gangrene with no revascularisation target
• Osteomyelitis destroying the midfoot or hindfoot architecture
• Non-ambulatory patients for whom a shorter operation and a prosthesis may genuinely be safer
• Patients who cannot off-load — a flap on a foot that keeps taking full weight will fail

Amputation is not a failure of care. A well-planned, well-fitted below-knee amputation with rehabilitation beats a salvaged foot that never heals, keeps the patient septic and bedbound for a year. The mistake is not choosing amputation; it is choosing it by default, without assessment.

Prevention, which is where most of the value is

• Inspect the feet daily — mirror for the sole, or a family member
• Never walk barefoot, including at home
• Off-load every ulcer from day one; a total contact cast or a well-made insole
• Control glucose and stop smoking; both change perfusion measurably
• Treat callus before it becomes an ulcer; trim nails straight
• See a foot service at the first sign of a wound that is not closing in two weeks

What to send if you are seeking a second opinion

Photographs of the wound with a ruler, the vascular studies and their reports, X-rays of the foot, HbA1c, and a note of which antibiotics have already been used. With that, a salvage team can tell you whether the foot is a flap case, a revascularisation-then-flap case, or a case where a good amputation is the kinder answer.