Effect of Level of Sensitization on Gait in Chronic Low Back Pain: Insights from a Machine Learning Approach

Abstract

Background: Despite central sensitization (CS) often presents in patients with chronic low back pain (CLBP), there is a lack of quantitative and qualitative analysis of the effect of CS on gait performance. The study aimed to investigate the daily-living gait performance of patients with CLBP with low and high CS levels (CLBP- and CLBP+, respectively). Method：Forty-two patients with CLBP were included. CS was assessed by Central Sensitization Inventory (CSI). Patients were classified according to low or high CSI score (23 CLBP- and 19 CLBP+). Patients wore a 3D accelerometer for about one week. From each patient, 4 days of accelerometer-data were randomly selected. For each day data, continuous gait cycles were extracted using a Fast Fourier Transform-based and a zero-cross method. For all gait cycles in one day, 36 gait outcomes representing variables related to pace, regularity, smoothness, local stability and predictability of gait were calculated. A Random Forest classifier was trained to classify CLBP- and CLBP+ groups based on gait outcomes and SHapley Additive exPlanations (SHAP) method was used to explain the differences between groups in gait outcomes. Results：The Random Forest classifier could accurately recognize the CLBP- and CLBP+ groups (accuracy = 84.4%, F1-score = 82.6%). SHAP reported that the most differences between CLBP- and CLBP+ groups were: index of harmonicity-vertical and harmonic ratio-mediolateral (gait smoothness), stride frequency variability- mediolateral/anteroposterior, stride length variability (gait variability), stride regularity-mediolateral (gait regularity), maximal Lyapunov exponent-vertical/mediolateral and maximal Lyapunov exponent per stride-vertical (gait stability), and sample entropy-anteroposterior (gait predictability). Conclusions： CLBP- and CLBP+ presented different motor control strategies. CLBP- presented a more “loose” control, including higher gait smoothness and stability. CLBP+ presented a more “tight” control, including a more regular, less variable and more predictable gait pattern.