The Amputee Mobility Predictor: An instrument to assess determinants of the lower-limb amputee's ability to ambulate

Objectives: To describe the development of the Amputee Mobility Predictor(C) (AMP) instrument designed to measure ambulatory potential of lower-limb amputees with (AMPPRO) and without (AMPnoPRO) the use of a prosthesis, and to test its reliability and validity. Design: Measurement study using known groups method and concurrence with existing measures. Setting: Academic medical center. Participants: A convenience sample of 191 lower-limb amputee subjects who had completed prosthetic training, 24 in the reliability study (mean age +/- standard deviation, 68.3 +/- 17.9y, range, 28-99y) and 167 in the validity study (mean age, 54.8 +/- 8.6y; range, 18-100y). Interventions: Not applicable. Main Outcome Measures: Intra- and interrater reliability; construct validy by known groups method; concurrent validity by comparisons with 6-minute walk test, Comorbidity Index, age, and time since amputation; predictive validity by comparison with 6-minute walk test after controlling for other factors. Results: Interrater reliability was.99 for subjects tested with and without their prosthesis; intrarater reliability was .96 and .97. Both the AMPnoPRO (P<.0001) and the AMPPRO scores (P<.0001) distinguished among the 4 Medicare functional classification levels. The AMP correlated strongly with 6-minute walk scores (AMPnoPRO r=.69, P<.0001; AMPPRO r=.82, P<.0001) and the amputee activity survey (AMPnoPRO r=.67, P<.0001; AMPPRO r=.77, P<.0001), and negatively correlated with age (AMPnoPRO r= -.69, P<.0001; AMPPRO r=.56, P<.0001) and comorbidity (AMPnoPRO r= -.43, P<.0001; AMPPRO r=.38, P<.0001). Conclusion: The AMP with and without a prosthesis are reliable and valid measures for the assessment of functional ambulation in lower-limb amputee subjects.