Purpose: To develop a valid measure of lower limb amputee mobility suitable for routine clinical use, including monitoring change.
Methods: The Special Interest Group in Amputee Medicine (SIGAM) described a single-item scale comprising six clinical grades (A-F) of amputee mobility. A self-report questionnaire was developed and algorithm designed to facilitate grade assignment. Reproducibility of the questionnaire and grades were assessed in 62 amputees. Concurrent validity and sensitivity to change were investigated using the timed walking test (TWT). The mobility construct was examined in 200 amputees, using item response theory, by co-calibration with the Rivermead Mobility Index (RMI) on the same patients.
Results: Patients included 144 males and 66 females, aged 13-90. Intraclass correlation coefficients and reproducibility kappa values were satisfactory. Observers agreed 100% in using the algorithm. TWT improved as SIGAM grade increased. Examination of psychometric properties revealed the SIGAM item fitted within the RMI mobility matrix. Average measures for the six grades were ordered correctly. There was no local dependency or differential item functioning for clinically relevant patient subgroups. The SIGAM scale showed an effect size of 10.66.
Conclusions: The SIGAM mobility grades represent a novel, valid, clinically useful measure of amputee mobility which is also sensitive to change.