Introduction: Approximately 75% of Medicare patients sustain vascular-related major lower-limb amputations and die within five years postamputation. Studies have examined factors influencing mortality rates at one and five years postamputation. Lower-limb prosthesis users are assigned Medicare Functional Classification Levels (i.e., K-levels) at prosthetic evaluations. Higher K-level patients tend to ambulate faster and have lower comorbidity index scores. To date, no known studies have examined K-level classification as a mortality indicator. The study objective was to examine mortality rates and major nontraumatic lower-limb amputation Medicare patient demographics in the Chicago metropolitan area. A secondary goal was to explore how K-level classification coincides with mortality rates.
Materials and Methods: A total of 2833 lower-limb prosthetic patient evaluation records ranging from June 2014 to February 2019 were exported from Futura Practice Management. Only Medicare patients with major lower limb amputations and information related to vascular etiologies were considered. Type and comorbidity quantity were assessed per record. K-levels used were those recorded; raw Amputee Mobility Predictor scores were not considered. The patients' living status was based on the dates of death found in the MYCGS database; living patients were assigned dates of database access. The number of days the patient survived postamputation was calculated as the difference between their living status and date of death. Descriptive statistics, binary logistic regression models with a confidence interval of 95%, and a 5-year Kaplan-Meier plot were generated in SPSS. A truth table was created to determine eligible records for use in plots and mortality calculations at five years postamputation.
Results: A total of 502 patients were included after the inclusion criteria application. Overall mortality rates at one year and five years postamputation were 33.6% and 73.59%, respectively. Transtibial and transfemoral mortality rates and one-year and five years post-amputation were 33.07%, 72.32%, 35.59%, and 77.78%, respectively. Comorbidity quantity had no statistical significance or influence on mortality rates at one year and five years postamputation. End-stage renal disease (ESRD) and heart condition had greater mortality association and increased mortality by a factor of 2.3 and 2.4, respectively. Kaplan-Meier results suggest that as K-level classification increases, so too does cumulative survival.
Conclusions: One-year and 5-year overall mortality rates fell within the ranges reported in the literature (33.6%, 73.59%). Transtibial and transfemoral mortality at 1 and 5 years postamputation were 33.07%, 72.32%, 35.59%, and 77.78%, respectively. ESRD and heart condition were indicators of mortality relative to other comorbid conditions. Higher K-level was associated with greater survival probability per Kaplan-Meier results.
Clinical Relevance: ESRD demonstrated a greater association with mortality after one-year postamputation, and heart condition had a greater association with mortality at five years postamputation, suggesting that patients should be encouraged to adopt healthier lifestyles/choices. Their activity level and corresponding K-level suggest that goals driven toward K-level improvement may, in fact, improve their survival and reduce mortality. (J Prosthet Orthot.2023;00:00–00)
The number of amputations is expected to double by the year 2050 from 1.6 to 3.6 million patients. Fifty-four percent of amputations are related to vascular issues with diabetes mellitus (DM) diagnosed in approximately 66% of these patients.1A total of 74% of Medicare patients have comorbid diagnoses of DM and often undergo amputations secondary to vascular-related (i.e., nontraumatic) etiologies.2
Mortality rates vary depending on amputation level, population demographics, and geography.3–12 Overall mortality rates range from 44% to 48.3% at one year postamputation and 50% to 82% at five years.3–14 Patients with transtibial amputations (TTAs) secondary to vascular-related issues have mortality rates at 1 and 5 years ranging from 29.6% to 33% and 40% to 82%, respectively.3–7,9,10,12,14 Mortality rates at one and five years post-amputation for patients with transfemoral amputations (TFAs) have been reported at 30.6% to 58% and 40% to 90%, respectively.5–7,9,10,12 Despite population differences, certain variables consistently influence mortality rates. Correlative factors for mortality rates are increased age, race, comorbid conditions (type and quantity), and amputation level.4,5,7–10,12–14 One unexplored variable in mortality studies in individuals with amputation is Medicare Functional Classification Levels (MFCLs), known colloquially in prosthetic care as K-levels. K-levels are assigned to Medicare beneficiaries by physicians, prosthetists, or physical therapists based on information acquired through stringent evaluations. Beneficiaries are assigned one of five functional levels based on their functional expectation (Table 1).15,16
Patients assigned higher K-levels tend to perform better on performance-based outcome measures.17,18 One temporal variable of interest has been gait speed. Speed has been demonstrated to be a determinant in patient longevity. Stanaway et al.19 found that able-bodied men in their 70s ambulating at rates slower than 0.82 m/s had a 1.23 times greater likelihood of dying than those ambulating at faster speeds. Prosthetists already work with a mobility-impaired population that is predisposed to ambulating at decreased speeds relative to able-bodied individuals 20,21Patients classified at lower K-levels have been observed ambulating at slower rates and will, therefore, be at an increased risk of premature death relative to patients classified at higher K-levels.17,18
Anecdotally, it is believed that our patients have been perceived as outliving the 5-year mortality rates reported. The objective of this study was to examine the mortality rates and demographics, particularly age, sex, and race, of patients with a major nontraumatic lower-limb amputation at a large metropolitan private prosthetic and orthotic practice in Chicago, Illinois. A secondary goal was to explore the comorbidities reported within the literature and their influence on the observed mortality rates, as well as how K-level contributes to the observed mortality rates.