A 66-year-old man with type 2 diabetes of 10 years' duration went to casualty complaining of a swollen foot with a small purple area on the medial border. His foot pulses were impalpable and his pressure index was 0.7. He was unwell with pyrexia of 39°C and had rigors. He was taken to operating theatre for debridement. Although the area of non-viable tissue appeared to be not more than 3 cm in diameter (Fig. 6.23a), surgical debridement revealed very extensive tissue destruction involving subcutaneous tissues and bones. He underwent excision of the 1st toe, 1st metatarsal, medial cuneiform and navicular, and large areas of skin and soft tissue. Apparently healthy overlying skin covered a layer of necrosis which had tracked between skin and subcutaneous tissues like the filling of a sandwich. One week later the wound was not granulating (Fig. 6.23b). He did not want a bypass but agreed to undergo angioplasty of stenoses in his popliteal artery and tibioperoneal trunk, after which the wound granulated well (Fig. 6.23c). He was discharged after 3 months for shared care of his healing wound between community nurses and the diabetic foot clinic. However, he died of a myocardial infarct the same day.
• Surface appearances can be very deceptive: the visible area of discolouration is usually just the tip of the iceberg
• Apparently healthy skin can cover extensive necrosis
• It is often only when surgical debridement is performed that the true extent of necrosis is understood
• If the pressure index is low and the wound is not granulating vascular intervention shoud be carried out
• It may take several weeks for the optimal effects of an angioplasty to take effect and granulation of the wound to take place.
Careful sharp debridement is performed along the demarcation line between necrosis and viable tissue to debulk dead tissue, drain pockets of pus and prevent accumulation of debris (Fig. 6.24a,b). Scalpel and forceps are used: if necrotic material is moist then traction should be applied with the forceps to enable precise cutting with the scalpel. If tension is not applied it will be impossible to clear away the moist necrosis and the operator is in danger of cutting the patient.
If areas of the necrotic toe are moist and the necrosis is full thickness (deep to bone) then the necrotic portion may be best removed by amputating it through the inter-phalangeal joint distal to the demarcation line between necrosis and viable tissue. The removed necrotic apex can be sent to the laboratory for culture. Once this procedure has been performed it is easier to debride necrotic material from around the stump without damaging viable tissue. The patient should always be warned and consulted if this procedure is to be attempted.
We remember one patient who watched with interest while his necrotic toe was amputated and asked if he could take it home. When asked why he wanted it he explained that he was meeting friends at the pub that evening and intended to drop the toe into someone's beer. The diabetic foot clinic staff confiscated the offending toe!
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