Validity of the de Morton Mobility Index (DEMMI) for measuring the mobility of patients with hip fracture during rehabilitation.

Abstract

Many patients suffer long term loss of mobility after hip fracture but there is no gold standard method for measuring mobility in this group. We aimed to validate a new mobility outcome measure, the de Morton Mobility Index (DEMMI) in a hip fracture population during inpatient rehabilitation. The DEMMI was compared with the existing measures of activity limitation: 6 minute walk test, 6 metre walk test and Barthel Index on 109 consecutive patients admitted to rehabilitation after surgery for hip fracture. Patients were assessed by a physiotherapist at admission and discharge. Scale width, validity, minimal clinically important difference (MCID), responsiveness, and unidimensionality were investigated. Evidence of convergent, discriminant and known groups validity were obtained for the DEMMI. Responsiveness was similar across instruments and the MCIDs were consistent with previous reports. A floor effect was identified for the 6 metre walk test and 6 minute walk test at hospital admission. Rasch analysis identified that the DEMMI maintains its unidimensional properties in this population. The DEMMI has a broader scale width than existing measures of activity limitation and provides a unidimensional measure of mobility for hip fracture patients during inpatient rehabilitation.