Modifying the Mobility Scale for Acute Stroke (MSAS) for All Stroke Phases (MSAS): Measurement Properties and Clinical Application

Objective: To develop and examine the measurement properties and interpretability of the Mobility Scale for "All" Stroke Phases (MSAS) as a potential single outcome measure to capture improvements in physical function throughout the stroke continuum.

Design: Retrospective cross-sectional study.

Setting: Inpatient rehabilitation unit.

Participants: People after stroke at discharge from rehabilitation (N=309).

Intervention: Not applicable.

Main Outcome Measure(s): We developed MSAS by extending the highest MSAS level (walk 10 m independently) with 4 gait speed levels. To establish a clinical anchor, we extracted a 4-level discharge outcome. To assess the distributional properties and internal consistency of MSAS, we evaluated its ceiling effects and calculated the Cronbach alpha, respectively. To assess structural validity, we performed a confirmatory factor analysis. To assess (i) its convergent validity with the FIM and (ii) its predictive validity with the clinical anchor, we used Spearman's rank correlations. To evaluate the clinical interpretability of MSAS, we used an item-response theory-based method to estimate MSAS thresholds associated with the clinical anchor.

Results: The MSAS had lower ceiling effects compared with MSAS (0% vs 25%). Internal consistency of MSAS was excellent (α=0.94). Structural validity of MSAS demonstrated a good fit (Comparative Fit Index=0.95; Tucker-Lewis Index=0.92; Root Means Square Error of Approximation=0.17). MSAS demonstrated a moderate correlation (rho=0.66) with FIM score and with the clinical anchor (rho=0.75). MSAS thresholds for increasing levels of the clinical anchor were 22 (20.8 to 23.6) - at least moderate assistance with walking/transfers, 28 (27.5 to 29.4) - at most supervision with walking, and 33 (32.5 to 33.4) - able to walk unassisted.

Conclusion: The MSAS showed adequate measurement properties and clinical interpretability. MSAS has the potential to be a single universal measure to evaluate physical function after stroke but further evaluation of clinical interpretability is required.