Discriminative ability, responsiveness, and interpretability of smoothness index of gait in people with multiple sclerosis

Introduction: Gait impairments are common in People with Multiple Sclerosis (PwMS). Several studies have examined the clinometric properties of Inertial Measurement Units (IMUs), with LDLJa identified as a robust metric for gait smoothness. However, its responsiveness and interpretability have not been explored. Methods: This cross-sectional study at IRCCS Santa Lucia Hospital enrolled 44 PwMS (age: 28-71; EDSS: 0-6) and 43 age- and gait-speed-matched healthy participants (HP). Two physiotherapists conducted assessments with five synchronized IMUs during a 10-meter walk at participants' preferred speed. Data were collected at baseline (T0) and after 4 weeks of training (T1). Results: Significant differences in log dimensionless jerk (LDLJa) were found between PwMS and HP in the AP (p < 0.001, d = 0.63), ML (p < 0.001, d = 1.08), and CC (p = 0.03, d = 0.68) directions. PwMS had lower LDLJaAP values (< -4.88) and LDLJaML values (< -5.40) with probabilities of 63% and 76%, respectively. ΔLDLJaML demonstrated good responsiveness to rehabilitation (AUC ~0.80), with improvements >4.02% representing the optimal MCID for clinical improvement in MiniBesTest. Conclusion: Lower LDLJa values in the AP and ML directions characterize gait smoothness impairment in PwMS. LDLJa in the ML direction is responsive to balance-focused rehabilitation, highlighting its potential for tracking gait disorders and rehabilitation progress.