Differences in kinematic parameters and plantarflexor reflex responses between manual (Ashworth) and isokinetic mobilisations in spasticity assessment

Objective The purpose of this study was first to compare the kinematic parameters of imposed ankle mobilizations measured during Ashworth or isokinetic tests and, second, to better understand why the stretch reflex was more or less easily elicited by one method or the other. Methods Passive dorsiflexions were applied on eight adult patients with plantarflexor spasticity in two conditions: (i) manually, using the Ashworth test where passive dorsiflexions were performed freely by seven rehabilitation clinicians, and (ii) instrumentally, using an isokinetic device (Cybex® Norm™) and a dorsiflexion velocity at 300°/s. Mean values of initial ankle position, maximal angular velocity (θ′max), maximal angular acceleration (θ″max) and plantarflexor reflex responses obtained with each method were compared. Results During the Ashworth test, all the patients presented reflex activities in the triceps surae while, during the isokinetic mobilization, only three out of the eight patients tested shown reflex responses. θ′max values were significantly higher (P<0.05) in the manual test (308±80°/s vs 216±5.5°/s for the isokinetic test). The most marked difference concerned the θ″max values (5046±2181°/s2 for the Ashworth test vs 819±18°/s2 for the isokinetic test, P<0.001). This parameter was significantly correlated with the mean rms-EMG values of the gastrocnemius lateralis (GL) and the soleus (SOL). Conclusions This study indicates that passive dorsiflexions imposed during Ashworth and isokinetic tests largely differ in velocity and acceleration, and the higher dynamic parameters evaluated during the Ashworth test could mainly explain that the stretch reflex was more easily elicited during this manual testing. Significance If isokinetic devices offer numerous advantages in the assessment of passive resistance to spastic muscle stretch, they cannot be used to simulate the manual test.