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

OBJECTIVE: To develop and examine the measurement properties and interpretability of the Mobility Scale for "All" Stroke Phases (MSAll S) 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 MSAll S by extending the highest MSAS level (walk 10m 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 MSAll S, 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 Functional Independence Measure (FIM) and (ii) its predictive validity with the clinical anchor, we used Spearman's rank correlations. To evaluate the clinical interpretability of MSAll S, we used an item-response theory-based method to estimate MSAll S thresholds associated with the clinical anchor.

RESULTS: The MSAll S had lower ceiling effects compared with MSAS (0% vs 25%). Internal consistency of MSAll S was excellent (α = 0.94). Structural validity of MSAll S demonstrated a good fit (Comparative Fit Index =0.95; Tucker-Lewis Index=0.92; RMSEA = 0.17). MSAll S demonstrated a moderate correlation (rho=0.66) with FIM score and with the clinical anchor (rho=0.75). MSAll S 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 MSAll S showed adequate measurement properties and clinical interpretability. MSAll S has the potential to be a single universal measure to evaluate physical function after stroke but further evaluation of clinical interpretability is required.