"PNP slows down" - linearly-reduced whole body joint velocities and altered gait patterns in polyneuropathy

Abstract

Introduction: Gait disturbances are a common consequence of polyneuropathy (PNP) and a major factor in patients' reduced quality of life. Less is known about the underlying mechanisms of PNP-related altered motor behavior and its distribution across the body. We aimed to capture whole body movements in PNP during a clinically relevant mobility test, i.e., the Timed Up and Go (TUG). We hypothesize that joint velocity profiles across the entire body would enable a deeper understanding of PNP-related movement alterations. This may yield insights into motor control mechanisms responsible for altered gait in PNP.

Methods: 20 PNP patients (61 ± 14 years) and a matched healthy control group (CG, 60 ± 15 years) performed TUG at (i) preferred and (ii) fast movement speed, and (iii) while counting backward (dual-task). We recorded TUG duration (s) and extracted gait-related parameters [step time (s), step length (cm), and width (cm)] during the walking sequences of TUG and calculated center of mass (COM) velocity [represents gait speed (cm/s)] and joint velocities (cm/s) (ankles, knees, hips, shoulders, elbows, wrists) with respect to body coordinates during walking; we then derived mean joint velocities and ratios between groups.

Results: Across all TUG conditions, PNP patients moved significantly slower (TUG time, gait speed) with prolonged step time and shorter steps compared to CG. Velocity profiles depend significantly on group designation, TUG condition, and joint. Correlation analysis revealed that joint velocities and gait speed are closely interrelated in individual subjects, with a 0.87 mean velocity ratio between groups.

Discussion: We confirmed a PNP-related slowed gait pattern. Interestingly, joint velocities in the rest of the body measured in body coordinates were in a linear relationship to each other and to COM velocity in space coordinates, despite PNP. Across the whole body, PNP patients reduce, on average, their joint velocities with a factor of 0.87 compared to CG and thus maintain movement patterns in terms of velocity distributions across joints similarly to healthy individuals. This down-scaling of mean absolute joint velocities may be the main source for the altered motor behavior of PNP patients during gait and is due to the poorer quality of their somatosensory information.

Clinical trial registration: https://drks.de/search/de, identifier DRKS00016999.

Keywords: TUG; gait; instrumented timed-up-and-go; joint velocity; motor control; polyneuropathy; whole-body motion capture.

Figure 1

Mean joint velocities. The figure shows the mean joint velocities relative to the center of mass (in body coordinates) (y-axis) extracted from the waking sequences during the timed up and go test (TUG) per group [CG (red), control group; PNP (blue), patients with peripheral neuropathy]: (A) average value per joint (x-axis) across all conditions and (B) per condition (P, preferred; DT, dual-task; F, fast condition) across joints. Boxplots showing the lower quartile (25th percentile), median (50th percentile), upper quartile (75th percentile), and degree of dispersion as 95% confidence interval (95% CI) (whiskers).

Figure 2

Correlations. (A) Correlations between the center of mass (COM) representing gait speed (x-axis) and joint velocity (y-axis) across conditions exemplarily for the ankle (top) and hip (bottom) joint velocities per group [CG (red), control group; PNP (blue), patients with peripheral neuropathy], including the regression equation, R-squared and value of p, respectively. (B) Displays the mean velocity ratio of 0.87 between groups (see regression equation). Boxes and whiskers show the mean velocities (box) and standard deviation [horizontal whiskers for CG, vertical whiskers for PNP) of the CG (x-axis) against the PNP group (y-axis) per condition (P (red), preferred; DT (blue), dual-task; F (green), fast condition] across joints.