Understanding The Biomechanics Of The Transmetatarsal Amputation
In a thorough review of the literature on the transmetatarsal amputation in patients with diabetes, these authors discuss keys to proper patient selection, essential biomechanical aspects of the procedure, when adjunctive procedures can have an impact and tips on post-op shoe gear.
Non-traumatic lower extremity amputation (LEA) in the United States is attributed to diabetes more than any other disease with an overall incidence of 195 per 100,000 person-years. This number will likely continue to climb as the number of patients afflicted with diabetes increases and life expectancy continues to rise.1,2 Consequently, the podiatric surgeon will encounter increasing numbers of pedal complications associated with the disease that require surgical intervention to prevent major limb loss and the associated cardiovascular compensatory ramifications.
Limb preservation in the diabetic population remains challenging and is most effective utilizing a multidisciplinary approach.3 This multidisciplinary team includes the podiatric surgeon, vascular surgeon, infectious disease specialist, internal medicine physician, interventional radiologist, plastic surgeon and rehabilitation specialists among others. Primary objectives include maximizing function; minimizing the risk of tissue breakdown and the need for a more proximal amputation; and avoiding the morbidity and mortality associated with major limb amputation and the need for intensive rehabilitation.
When surgeons perform the transmetatarsal amputation (TMA) correctly and in combination with adjunctive procedures when necessary, the TMA is a valuable surgery in the limb salvage effort, and preferred over a below- or above-knee amputation when functionally and physiologically reasonable with authors reporting success rates of over 90 percent.4 The TMA enables patients to better sustain a quality of life as most patients will not require the help of others to perform activities of daily living, and the likelihood of patients ambulating independently is greater than those who have had transtibial and transfemoral amputations. Researchers have shown that oxygen consumption increases up to 280 percent of normal during ambulation in patients with major limb amputations.5
Furthermore, 30-day mortality rates for below- and above-knee amputations are much higher than those for TMAs with authors reporting rates as high as 6.3 percent and 13.3 percent while survival probabilities decrease to 28 percent and 20 percent for below- and above-knee amputations, respectively, at 7.5 years postoperatively.6 Other researchers have reported significantly better 30-day mortality rates for TMA with rates being less than 2 percent.7,8
Keys To The Clinical Exam And Pertinent Perioperative Considerations
During routine clinical examination of the patient with diabetes, it is critical to identify the risk factors that predispose patients to the sequelae associated with abnormal physiology proceeding from longstanding and/or poorly controlled hyperglycemia. These risk factors may be neurological, vascular or biomechanical in nature.
It is well known that peripheral sensory neuropathy and peripheral vascular disease (PVD) are independent risk factors for lower extremity amputation in patients with diabetes. Peripheral vascular disease is associated with a threefold increased risk of lower extremity amputation and peripheral sensory neuropathy is a risk factor for minor amputation.9 Furthermore, a meta-analysis comprised of 14 studies and 94,640 participants determined the risk of lower extremity amputation to increase by 26 percent with one percentage point increase in HbA1c.10