Below knee amputation may be necessary for people with critical limb ischaemia caused by advanced vascular disease or diabetic foot infection (sepsis) where no other treatment option is possible. Keeping the knee joint gives a better chance of walking using an artificial leg or prosthesis and social independence after the amputation. The surgical technique is important. Bone and deep tissues are generally treated in a similar way but the type of skin incision varies between techniques. A skin flap is designed to go over the stump where the main consideration is to maximise blood supply and healing. A long posterior skin flap and unequal (skewed) anterior and posterior muscle and skin (myocutaneous) flaps are most often used, although other techniques have been described.
Three randomised controlled studies were identified. They were reported on between 1977 and 1991 and involved a total of 309 patients. Each reported on different comparisons. Below knee amputation using skew flaps or sagittal flaps provided no advantage over the long posterior flap technique on primary stump healing, which approached 60% for all groups. In the third study, involving 30 patients with wet gangrene, a two-stage procedure with a guillotine amputation at the ankle followed by long posterior flap amputation led to better primary stump healing than a one-stage procedure with delayed skin closure. Post-operative infection rate or wound necrosis, reamputation and mobility with a prosthetic limb were similar in the different comparisons.
Nearly all the surgeons in the study that looked at skew flap amputation versus the long posterior flap technique were new to the skew flap operation and so were on a learning curve. Factors which might have influenced the findings include previous experience of a technique, the extent of non-viable tissue and location of pre-existing surgical scars.