Application of 3D motion analysis to quantify a clinical test method assessing wrist spasticity

Spasticity is a symptom that occurs in patients with acute or chronic damages of the central nervous system [1]. Quantification of such limitations is essential, for example for preoperative decision making. Though, objective measurement methods to assess upper limb (UL) spasticity are poorly applied in clinical practice. Due to the low interrater reliability of subjective scales (modified Ashworth scale (MAS), modified Tardieu scale (MTS) [2,3]), 3D motion analysis and synchronized surface EMG (sEMG) should be used as an alternative method to determine objective parameters. How do the results of the objective sEMG parameters during passive stretch correlate with the subjective values of MAS and MTS? Which differences exist in wrist kinematics and muscle activity during a passive stretch of the wrist flexors between healthy adults and patients with UL spasticity? 11 patients with UL spasticity (39 ± 18 years) and 5 healthy adults (10 arms, 35 ± 9 years) were included. All participants were analysed using 3D motion analysis (Qualisys, U.L.E.M.A [4]) and sEMG (Noraxon) on M. flexor carpi ulnaris and / or M. flexor carpi radialis and M. extensor carpi radialis brevis during passive stretch of the wrist (3 slow (LV) and 3 quick (HV) directed movements). sEMG data were normalised to maximum isometric contraction (MVIC) and examined over a defined period of time (200ms before reaching maximum velocity to 90% of max. extension [5]). The velocity of the passive stretch (30°/s slow, 180°/s fast) was standardized with a metronome. The maximum passive wrist extension, the sEMG parameters (EMGLV and EMGHV) as well as the sEMG difference between LV and HV (EMGchange) were compared between groups (Mann-Whitney-U-Test). MAS and MTS were clinically assessed and correlated with sEMG parameters (Spearman's rank correlation coefficient). Joint angles and sEMG parameters were significantly different between groups (Table 1a). Correlations between sEMG based parameters and the subjective values of MAS and MTS where low and not significant (Table 1b). Table 1: a): Differences between healthy adults and patients, b): Spearman's rank correlation coefficient between subjective Scales (MAS, MTS) and objective Parameters (EMGLV, EMGHV, EMGchange)Download : Download high-res image (74KB)Download : Download full-size image The objective measurement method, which has already been used for the elbow and lower limb, also shows promising results on the wrist. The comparison between healthy adults and spasticity patients clearly shows that the muscular activity of the wrist flexors during their passive stretch is high and velocity dependent in spasticity patients. Interestingly, neither MAS nor MTS values correlate to objective values at the wrist. Wrist flexor spasticity is not only caused by the wrist flexors, but also by the extrinsic finger flexors, which are not yet included in this model.