Abstract
Introduction: Differentiating between the components of wrist hyper-resistance post stroke, i.e., pathological neuromuscular activation (“spasticity”) and non-neural biomechanical changes, is important for treatment decisions. This study aimed to assess the reliability and construct validity of an innovative measurement device that quantifies these neural and non-neural components by biomechanical modeling.Methods: Forty-six patients with chronic stroke and 30 healthy age-matched subjects were assessed with the NeuroFlexor, a motor-driven device that imposes isokinetic wrist extensions at two controlled velocities (5 and 236°/s). Test-retest reliability was evaluated using intraclass correlation coefficients (ICC) and smallest detectable changes (SDC), and construct validity by testing the difference between patients and healthy subjects and between subgroups of patients stratified by modified Ashworth scale (MAS), and the association with clinical scales.Results: Test-retest reliability was excellent for the neural (NC) and non-neural elastic (EC) components (ICC 0.93 and 0.95, respectively), and good for the viscous component (VC) (ICC 0.84), with SDCs of 10.3, 3.1, and 0.5 N, respectively. NC and EC were significantly higher in patients compared to healthy subjects (p < 0.001). Components gradually increased with MAS category. NC and EC were positively associated with the MAS (rs 0.60 and 0.52, respectively; p < 0.01), and NC with the Tardieu scale (rs 0.36, p < 0.05). NC and EC were negatively associated with the Fugl-Meyer Assessment of the upper extremity and action research arm test (rs ≤ −0.38, p < 0.05).Conclusions: The NeuroFlexor reliably quantifies neural and non-neural components of wrist hyper-resistance in chronic stroke, but is less suitable for clinical evaluation at individual level due to high SDC values. Although construct validity has been demonstrated, further investigation at component level is needed.
Highlights
Differentiating between the components of wrist hyper-resistance post stroke, i.e., pathological neuromuscular activation (“spasticity”) and non-neural biomechanical changes, is important for treatment decisions
The relatively high smallest detectable changes (SDC) values we found, with good to excellent intraclass correlation coefficients (ICC) values, can be explained by the heterogeneity of the study population we included, as ICC is strongly influenced by the variability between patients, whereas this variability is not included in the calculation of the SDC
The difference in the neural component we found between healthy subjects and patients in the modified Ashworth scale (MAS) = 0 category emphasizes the presence of hyperexcitability of the stretch reflex in all patients, even without clinical hyper-resistance [34]
Summary
Differentiating between the components of wrist hyper-resistance post stroke, i.e., pathological neuromuscular activation (“spasticity”) and non-neural biomechanical changes, is important for treatment decisions. The modified Ashworth scale (MAS) is routinely used as a clinical measurement scale for spasticity, as it is applicable, time-efficient and cost-free This ordinal rating scale has poor measurement properties regarding reliability [6,7,8] and validity [6, 8,9,10], and is unable to discriminate between spasticity and other factors influencing joint hyper-resistance. Various instrumented measurement setups using different modeling techniques were developed [11,12,13,14] These are generally time-consuming and require extensive training. Information regarding the validity of the different components compared to commonly used clinical scales is lacking
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