Mortality and Conversion Rate to Below Knee or Above Knee Amputation Following Transmetatarsal Amputation

Abstract

Category: Midfoot/Forefoot; Diabetes; Other Introduction/Purpose: Non-traumatic lower extremity amputations (LEA), especially those performed in dysvascular and diabetic patients, are known to have poor long-term prognosis. Perioperative mortality has been reported at between 4 and 10%, and the 1 and 5 year mortality rates range between 22-33% and 39-69%, respectively. While poor outcomes in these patients have been described, there is no consensus as to the predictors of mortality. The purpose of the study is to determine the percentage of patients who had a complication following transmetatarsal amputation (TMA) and identify associated risk factors for complications and mortality. Methods: We queried our institution’s administrative database to identify 247 TMA procedures performed in 229 patients between January, 2002 and December, 2016. Electronic health records were reviewed to document complications defined as reoperation, amputation and mortality. Mortality was also verified using the National Death Index. Additionally, we recorded risk factors including diabetes, A1c level, end stage renal disease (ESRD), cardiovascular disease (CVD), peripheral vascular disease (PVD), history of revascularization, contralateral amputation, and neuropathy. The majority of the study patients were males (157, 69%) and the average age was 57 years (range 24-91). The median BMI was 28 (range 16-58) and 29% of the study patients were obese with a BMI ≥ 30. Fishers Exact tests were used to compare categorical variables. Kruskal-Wallis and Independent T-tests were used to compare numeric data. All data were analyzed using SAS/STAT software version 9.4 (Carey, NC) and a 0.05 level of significance was defined apriori. Results: The conversion rate to below (BKA) or above knee amputation (AKA) was 26% (64 of 247). Males (p=.0274), diabetics (p=.0139), patients in ESRD (p=.019), and patients with a history of CVD (p=.0247) or perioperative revascularization (p=.022) were more likely to undergo further amputation following an index TMA. BMI was significantly higher in patients requiring BKA/AKA (p=.0305). There were no significant differences in age (p=.2723) or A1c levels (p=.4219). The overall mortality rate was 35% (84 of 229). Diabetes (p=.0272), ESRD (p=.0031), history of CVD (p<.0001) or PVD (p=.0179) were all significantly associated with mortality. Patients who died were significantly older (p=.0006) and had significantly higher A1c levels (p=.0373). BMI was not significantly associated with mortality. Twenty-two patients who had 23 further amputations subsequently died. Conclusion: In our series of patients undergoing TMA, 26% underwent further amputation and 35% of patients died. Conversion rate to BKA or AKA occurred at a high rate regardless of preoperative revascularization or the use of tendo-achilles or gastrocnemius lengthening procedures. Male sex, diabetes, ESRD, history of CVD or revascularization are significant risk factors for further amputation. ESRD, diabetes, history of CVD or PVD, older age and higher A1c levels are significant risk factors for mortality. These data provide useful insight into risk factors to be emphasized when counseling patients and their families to establish realistic postoperative expectations.