Novel Application of the Reachable Workspace Outcome Measure in SMA

Topic:

Translational Research

Poster Number: 188 M

Author(s):

Juan Carlos Perez Ibarra, PhD, University of California, Irvine, Vicky Chan, DPT, University of California, Irvine, Raymond Diaz Rojas, BS, University of California Irvine, Evan Hemingway, PhD, Bioniks, Inc., Gregorij Kurillo, PhD, Bioniks, Inc., Louis Cheng, PhD, Bioniks, Jay Han, MD, University of California Irvine

Background: Despite significant advances in treatment, individuals with Spinal Muscular Atrophy (SMA) often face persistent motor impairments. There is a need for sensitive upper-limb performance outcome (PerfO) measures to assess the efficacy of new treatments that are not fully captured by clinician- or patient-reported scales. The Reachable Workspace (RWS) metric, calculated from standardized arm movements tracked using a validated depth camera system, has demonstrated excellent reliability and clinical relevance in various neuromuscular disorders. However, it has yet to be applied to SMA.

Objective: To evaluate the feasibility, test–retest reliability, and clinical validity of RWS metrics in adults with SMA.

Results: Seventeen adults with SMA participated (39.3±13.3 years; 4 Type II, 12 Type III, 1 Type IV). Fourteen completed the full bilateral RWS assessments. RWS was feasible for all participants with SMAIS-ULM scores above 20 and NeuroQoL-UE scores above 50; however, only the three most-severely impaired Type II participants were unable to complete the protocol. The mean total four-quadrant and five-quadrant Relative Surface Areas (RSAs) were 0.56±0.24 and 0.65±0.29, respectively (typical healthy control total RSA range: 0.8-1.0), with no significant right–left differences (p=0.64). Test–retest reliability was strong (ICC: 0.83-0.98 for all RSAs). RWS showed strong clinical validity, with total RSA correlating with SMAIS-ULM (ρ=0.76), NeuroQoL-UE (ρ=0.73), and a self-reported version of the Hammersmith score (ρ=0.82), all p<0.01. Quadrant-level analyses revealed the strongest associations in Q1 and Q5 (ρ up to 0.86), reflecting the difficulties patients face with overhead and backward-reaching movements in SMA. Conclusions: This initial application of Reachable Workspace in SMA demonstrates feasibility across a wide range of disease severity, high reliability, and strong correlation with self-reported and perceived upper-limb function. These findings support RWS as a sensitive and objective performance outcome measure, suitable for integration into clinical trials and longitudinal monitoring in SMA.