Normative NeuroFlexor data for detection of spasticity after stroke: a cross-sectional study

Abstract

Background and objective: The NeuroFlexor is a novel instrument for quantification of neural, viscous and elastic components of passive movement resistance. The aim of this study was to provide normative data and cut-off values from healthy subjects and to use these to explore signs of spasticity at the wrist and fingers in patients recovering from stroke.

Methods: 107 healthy subjects (age range 28-68 years; 51 % females) and 39 stroke patients (age range 33-69 years; 33 % females), 2-4 weeks after stroke, were assessed with the NeuroFlexor. Cut-off values based on mean + 3SD of the reference data were calculated. In patients, the modified Ashworth scale (MAS) was also applied.

Results: In healthy subjects, neural component was 0.8 ± 0.9 N (mean ± SD), elastic component was 2.7 ± 1.1 N, viscous component was 0.3 ± 0.3 N and resting tension was 5.9 ± 1 N. Age only correlated with elastic component (r = -0.3, p = 0.01). Elasticity and resting tension were higher in males compared to females (p = 0.001) and both correlated positively with height (p = 0.01). Values above healthy population cut-off were observed in 16 patients (41 %) for neural component, in 2 (5 %) for elastic component and in 23 (59 %) for viscous component. Neural component above cut-off did not correspond well to MAS ratings. Ten patients with MAS = 0 had neural component values above cut-off and five patients with MAS ≥ 1 had neural component within normal range.

Conclusion: This study provides NeuroFlexor cut-off values that are useful for detection of spasticity in the early phase after stroke.

Keywords: Biomechanics; Muscle spasticity; Normative data; Stroke; Upper extremity.

Fig. 1

NeuroFlexor measurement device. The NeuroFlexor instrument showing the position of the hand with the metacarpophalangeal joints in slight flexion and the fingers completely extrended, and with the wrist axis of rotation aligned with the device. The instrument passively extends the wrist joint in a 50° range of motion with a starting angle of 20° of palmar flexion, and the movement is performed at controlled slow and fast velocities (5 and 236°/s, respectively)

Fig. 2

NeuroFlexor force traces. Example resistance profiles (N, newton) during slow and fast velocity movements in a young and old healthy subject and in two stroke patients. Blue traces show the angle of wrist movement (from flexion to extension). Red traces show mean resisting force from repeat trials and black traces shows mean resistance profiles when device runs without hand. Four time points are automatically identified by the software: P3 1 s after slow passive stretch; P0 in the beginning of the fast movement, P1 the first peak and P2 the peak towards the end of the fast movement. Values of neural (NC), elastic (EC) and viscous components (VC) are shown for each participant. Both healthy subjects show similar force profiles and have similar NC, EC, and VC components despite differences in age. In the patient examples the force increased during the fast movements (P2). While both patients presented NC values above normative cut-off (>3.4 N), only Patient 5 had a positive MAS score (see Table 2)

Fig. 3

Scatter plots NeuroFlexor variables. Scatter plots of neural (NC), elastic (EC) and viscous components (VC) and resting tension (P0), (N, newton) in healthy population (circles) and stroke patients (triangles). Note the increased NC above cut-off in many stroke patients