Is the Rivermead Mobility Index a suitable outcome measure in lower limb amputees? - A psychometric validation study

Objective: To examine the internal consistency, validity, responsiveness and test scalability of the Rivermead Mobility Index. Design: Methodological research (consecutive sampling, prospective longitudinal study). Patients: 140 unilateral lower limb amputees (79 above-knee and 61 below-knee). Methods: The Rivermead Mobility Index was administered to all patients at the beginning (T0) and at the end (T2) of the prosthetic training. In 70 of the patients, the Functional Independence Measure and a timed walking test were also carried out. Results: The Cronbach's alpha of the Rivermead Mobility Index was 0.85 and the item-to-total correlation coefficients rpb ranged from 0.33 to 0.74 (p < 0.0001), for the items considered, at T0; 4 correlations were not calculated due to the extremely low variability of some item responses (mode ≥98%). The correlation (rs) of Rivermead Mobility Index score with the motor subscale of the Functional Independence Measure was 0.83 at T0 and 0.69 at T2 (p < 0.0001, for both) and that with timed walking test -0.70 (p < 0.0001) at T2. The effect size was 1.35. The scalability coefficients were below the limits of acceptability. Conclusion: When applied in lower limb amputees, the Rivermead Mobility Index is an ordinal measure with adequate levels of a series of psychometric properties, which seems more useful for epidemiological studies than for clinical decision-making in single patients. Further steps should be considered to improve its item selection, response format and scaling properties.