Motor Unit Loss and Remodeling in Patients With Chronic Radiculopathy Using the EMG Filling Analysis.

Introduction/aims: The way in which the EMG signal is progressively filled with motor unit potentials during increasing voluntary contraction provides valuable information about the motor units (MUs) in a muscle. Here, we demonstrate the application of the EMG filling method to detect MU loss and remodeling in patients with chronic radiculopathy.

Methods: Concentric needle EMG signals were recorded from the tibialis anterior of 19 radiculopathy patients and 18 healthy controls during voluntary ramped contractions increasing from 0 to maximum. The EMG filling process was analyzed by measuring the EMG filling factor and EMG amplitude during the contraction.

Results: The way in which the filling factor increased with increasing force differed (p < 0.001) between healthy controls (exponential filling curve) and radiculopathy patients (linear curve). The extent to which the EMG envelope amplitude increased throughout the ramp contraction was markedly greater (p < 0.001) in healthy controls (6.1-fold increase) compared to patients (0.5-fold increase). The filling factor at maximal effort was significantly higher in healthy controls than in patients (0.53 ± 0.04 vs. 0.45 ± 0.09, p < 0.001). The EMG filling analysis revealed clear signs of MU loss and remodeling in 85% of patients.

Discussion: The EMG filling analysis is a fast and accessible approach to detect MU loss in radiculopathy patients. Moreover, it provides information about the MU remodeling process and the type of motor units that are predominantly lost in the neurogenic condition.