(PC082) A Competing-Risk Prediction Model to Assess Return to Ambulation After Major Amputation

Objectives: Major lower extremity amputation is a life-altering event which can lead to the loss of ambulation and functional independence. While predictive models have been developed to counsel patients on their chances of ambulating, many have been shown to over-estimate this outcome, possibly because they do not incorporate mortality. We sought to predict return to ambulation following major amputation while accounting for the competing risk of death.

Methods: A single-center retrospective review was conducted of baseline-ambulatory patients who underwent major lower extremity amputation for any vascular indication from 2019-2024. Descriptive statistics were calculated for baseline and surgical demographics. A multivariable Fine-Gray model of return to ambulation with competing risks of conversion to higher amputation and death was developed using a backward stepwise approach.

Results: In total, 262 patients underwent major amputation [below-knee: 193 (73.7%), above-knee: 69 (26.3%)] during the study period. The mean±SD patient age was 67.4 years ±12.2, 72.5% (n=190) were male, 31.7% (n=83) had prior minor amputation, 72.9% (n=191) had diabetes mellitus, and 64.9% (n=170) had known peripheral arterial disease. The baseline characteristics of those who did and did not return to ambulation were similar. The mean duration of available follow-up was 1.2 years ±1.3. There were 85 patients (32.4%) who died in follow-up with an unadjusted 1-year cumulative incidence of all-cause mortality of 57.9% [45.5-67.4] (Fig 1). By the end of follow-up, 32.4% of patients (n=85) had ambulated with a prosthetic; 38.9% for below-knee (n=75) and 14.5% for above-knee (n=10; p=0.0004). Thirty-three patients (12.6%) were converted to a higher level of amputation and 8 (24.2%) ambulated following conversion. The adjusted 1-year cumulative incidence of ambulation in surviving patients was 39.3% [20.4-53.7] after below-knee amputation and 22.2% [5.7-35.7] after above-knee amputation (Fig 2). Pre-operative multivariable factors that influence return to ambulation after major amputation, in surviving patients, included patient age (sHR [95%CI]: 0.8 per 10 years [0.7-1]; p=0.02), male sex (1.6 [1-2.7]; p=0.04), baseline creatinine >1.8 (0.5 [0.3-0.9]; p=0.01), above-knee amputation (0.4 [0.2-0.8]; p=0.01), and history of peripheral arterial disease (0.6 [0.4-0.9]; p=0.01; c-statistic 0.65).

Conclusions: This study demonstrated a low incidence of return to ambulation at 1-year after major lower extremity amputation, which was, in part, explained by the competing risk of mortality. While the outlook for these patients may be bleak, realistic expectation-setting is an important element of patient counseling with potential to impact goals-of-care discussions. Additional efforts are needed to validate this model externally.