Feasibility of Smartphone-Based Markerless Motion Capture for Quantitative Gait Assessment in Pediatric Guillain–Barré Syndrome: A Two-Case Proof-of-Concept Study

This two-case proof-of-concept study evaluated the feasibility and clinical utility of a smartphone-based markerless motion capture system for quantitative gait assessment in pediatric Guillain-Barré syndrome (GBS). Two children with GBS underwent overground gait analysis using a dual-smartphone setup (OpenCap), and three-dimensional hip, knee, and ankle kinematics were computed via OpenSim. Case 1, a boy with treatment-related fluctuation, demonstrated marked abnormalities in swing-phase limb advancement and ankle push-off that improved after six weeks of rehabilitation in parallel with gains in muscle strength, balance, and ambulation. Case 2, a girl recovering from acute inflammatory demyelinating polyneuropathy, exhibited residual reductions in hip and knee flexion and impaired ankle control despite normal strength, consistent with vestibular dysfunction. All assessments were completed within routine clinical time constraints and produced analyzable kinematic data using only two smartphones. These findings indicate that smartphone-based markerless motion capture is a feasible and informative method for detecting gait impairment and recovery patterns in pediatric GBS and may serve as an accessible digital biomarker to complement standard clinical evaluations.