Quantitative measurement of resistance force and subsequent attenuation during passive isokinetic extension of the wrist in patients with mild to moderate spasticity after stroke

Abstract

Background: Spasticity is evaluated by measuring the increased resistance to passive movement, primarily by manual methods. Few options are available to measure spasticity in the wrist more objectively. Furthermore, no studies have investigated the force attenuation following increased resistance. The aim of this study was to conduct a safe quantitative evaluation of wrist passive extension stiffness in stroke survivors with mild to moderate spastic paresis using a custom motor-controlled device. Furthermore, we wanted to clarify whether the changes in the measured values could quantitatively reflect the spastic state of the flexor muscles involved in the wrist stiffness of the patients.

Materials and methods: Resistance forces were measured in 17 patients during repetitive passive extension of the wrist at velocities of 30, 60, and 90 deg/s. The Modified Ashworth Scale (MAS) in the wrist and finger flexors was also assessed by two skilled therapists and their scores were averaged (i.e., average MAS) for analysis. Of the fluctuation of resistance, we focused on the damping just after the peak forces and used these for our analysis. A repeated measures analysis of variance was conducted to assess velocity-dependence. Correlations between MAS and damping parameters were analyzed using Spearman's rank correlation.

Results: The damping force and normalized value calculated from damping part showed significant velocity-dependent increases. There were significant correlations (ρ = 0.53-0.56) between average MAS for wrist and the normalized value of the damping part at 90 deg/s. The correlations became stronger at 60 deg/s and 90 deg/s when the MAS for finger flexors was added to that for wrist flexors (ρ = 0.65-0.68).

Conclusions: This custom-made isokinetic device could quantitatively evaluate spastic changes in the wrist and finger flexors simultaneously by focusing on the damping part, which may reflect the decrease in resistance we perceive when manually assessing wrist spasticity using MAS. Trial registration UMIN Clinical Trial Registry, as UMIN000030672, on July 4, 2018.

Keywords: Biomechanics; Finger; Force attenuation; Muscle spasticity; Objective assessment; Rehabilitation; Resistance force; Stroke; Wrist.

Fig. 1

Motor-controlled isokinetic custom apparatus to measure the extension stiffness in wrist joint. A Configuration of the experimental setup. B Appearance of the device. Left side: Overall picture of the equipment and positioning of the forearm and hand compartment. The hands were fixed with all fingers extended to reflect not only the spasticity of wrist flexors but also that of the extrinsic finger flexors. Right side: Lateral view of the motor and encoder compartment. C Top view of the hand compartment: The force sensor with a sliding system and hand plate. D Detailed view of the motor and encoder compartment. The axis of rotation (dotted arrow) was aligned with the axis of the wrist joint (solid circle in C)

Fig. 2

Waveforms obtained by measurement and definitions. a Typical example of changes in resistance force and angular displacement in the wrist joint at each of three angular velocities (30, 60, 90 deg/s) with sequential measuring during 11 repetitions. b The difference between the peak forces (i.e. between the maximum and minimum forces) immediately after the start of extension was defined as the maximum resistance force (RF) (A). The force attenuation during the subsequent 2-s maintenance of the extended position was defined as the damping force (B). c The area from the timing of the peak resistance to the timing of the greatest attenuation of resistance was defined as the pure damping impulse (D), and the entire damping area under the curve (including the pure damping impulse) was considered the total damping impulse (C)

Fig. 3

Comparisons of various parameters among the 3 velocity conditions. The lower boundary of each box indicates the 25th percentile, the line within the box marks the median, and the upper boundary indicates the 75th percentile. Whiskers above and below each box indicate the maximum and minimum values, respectively. The open circles denote outliers. The Shapiro–Wilk test showed that not all data were normally distributed for each parameter. The nonparametric Friedman test followed by the post-hoc Wilcoxon signed-rank test with Holm’s correction was applied. The asterisks indicate significant differences (*P < 0.05, **P < 0.01) between conditions

Fig. 4

Comparisons between mild and moderate spasticity. In each of the 3 velocity conditions for the damping force ratio (a) and the damping impulse ratio (b). The asterisks indicate significant differences (*P < 0.05, **P < 0.01, ***P < 0.001) between groups. The Shapiro–Wilk and Levene statistical tests were used to examine the normality and equality of variance. According to the results of these tests, a two-sample t test (TT) or Wilcoxon-Mann–Whitney test (WMW) was applied for between-group analysis. The differences at 90 deg/s for both ratios and at 30 deg/s for the damping impulse ratio were analyzed by WMW; otherwise, TT was used