Major amputations: clinical patterns and predictors.
The major amputation rate is approximately 200 to 500/million/yr and occurs in patients presenting with an acute onset of critical leg ischemia (CLI) rather than in patients who steadily progress through increasingly severe claudication to rest pain and ulcers. Diabetics, who form only 2% to 5% of the population, form 40% to 45% of all amputees. Although it is widely believed that a below-knee (BK) to above-knee (AK) amputation ratio of 2.5 is the minimum acceptable for units providing a lower limb amputation service, the ratio is in fact usually very much below the recommended figure. The data suggest that primary healing of BK amputations ranges from 30% to 92% and the reamputation rate from 4% to 30%. If a popliteal pulse is palpable, then there is only a 10% failure rate, and bleeding during the operation does not seem to predict healing. Of the 30% of BK amputees whose wounds do not heal primarily, about half will need a higher major amputation, but once a BK major amputation has healed, only 4% of such patients ever need a higher amputation. A total of 90% of AK major amputations heal, 70% primarily. Two to three times as many BK amputees achieve full mobility than AK amputees, and there has not been any dramatic change in 20 years. The fate of the amputee 2 years after a successful BK amputation will be that 15% will have been converted to an AK amputation, another 15% will have had a contralateral major amputation, and 30% will be dead.