The development and validation of a novel outcome measure to quantify mobility in the dysvascular lower extremity amputee: the amputee single item mobility measure

Abstract

Objective: This study describes the development and psychometric evaluation of a novel patient-reported single-item mobility measure. Design: Prospective cohort study. Setting: Four Veteran’s Administration Medical Centers. Subjects: Individuals undergoing their first major unilateral lower extremity amputation; 198 met inclusion criteria; of these, 113 (57%) enrolled. Interventions: None. Main measures: The Amputee Single Item Mobility Measure, a single item measure with scores ranging from 0 to 6, was developed by an expert panel, and concurrently administered with the Locomotor Capabilities Index-5 (LCI-5) and other outcome measures at six weeks, four months, and 12 months post-amputation. Criterion and construct validity, responsiveness, and floor/ceiling effects were evaluated. Responsiveness was assessed using the standardized response mean. Results: The overall mean 12-month Amputee Single Item Mobility Measure score was 3.39 ±1.4. Scores for transmetatarsal, transtibial, and transfemoral amputees were 4.2 (±1.3), 3.2 (±1.5), and 2.9 (±1.1), respectively. Amputee Single Item Mobility Measure scores demonstrated “large” and statistically significant correlations with the LCI-5 scores at six weeks (r = 0.72), four months (r = 0.81), and 12 months (r = 0.86). At four months and 12 months, the correlation between Amputee Single Item Mobility Measure scores and hours of prosthetic use were r = 0.69 and r = 0.66, respectively, and between Amputee Single Item Mobility Measure scores and Trinity Amputation and Prosthesis Experience Scales functional restriction scores were r = 0.45 and r = 0.67, respectively. Amputee Single Item Mobility Measure scores increased significantly from six weeks to 12 months post-amputation. Minimal floor/ceiling effects were demonstrated. Conclusions: In the unilateral dysvascular amputee, the Amputee Single Item Mobility Measure has strong criterion and construct validity, excellent responsiveness, and does not exhibit floor/ceiling effects.