Effect of transdermal anesthetic phonophoresis on motor neurone excitability

Abstract EN

Objective: To investigate the effect of trans-dermal anesthetic phonophoresis on motor neuron excitability through measuring the amplitude of the soleus H-reflex and H/M ratio.

Materials & Methods: Thirty healthy male subjects of the same average age; weight and height participated in this study.

They were assigned randomly into two equal groups, consisting of 15 subjects each.

Each subject in both groups received treatment sessions and time interval sessions to investigate the effect of time on motor neuron excitability.

Group I received lidocaine ointment delivered to the skin over the proximal two-thirds of the left calf muscles with 1 MHz pulsed ultrasonic of 1.5w/cm² for 7.5 min.

Group II received pulsed ultrasonic only on the same area of application as in group I.

The subjects were treated with the same ultrasonic parameters and duration of treatment as in-group I.

The soleus H-reflex amplitude and H/M ratio were measured before and immediately after treatment and at intervals of 5, 10 and 15 minutes post-treatment in both groups.

Additional measurements at intervals of 20, 35 and 50 minutes post-treatment were done for group I to cover the duration of lidocaine efficacy.

Furthermore, the soleus H-reflex amplitude and H/M ratio were measured for all subjects at the same time intervals without application of treatment modalities to test the reliability of the H-reflex within the study.

Results: Time produced an insignificant change in the amplitude of the soleus H-reflex and H/M ratio, whereas lidocaine phonophoresis significantly decreased the soleus H-reflex amplitude and H/M ratio.

On other hand, pulsed ultrasound alone showed insignificant changes in the amplitude of the soleus H-reflex and H/M ratio through 15 min.

post-treatment, albeit it produced immediate significant reduction of both amplitude and ratio after treatment as compared with time interval.

Conclusion: Pulsed ultrasound did not have any significant effect on motor neuron excitability, albeit it was effective to enhance delivery and absorption of the trans-dermal anesthetic agent to the underlying tissues through the phonophoresis effect for 50 minutes.

Trans-dermal anesthetic phonophoresis is a safe, noninvasive and efficient modality to reduce motor neuron excitability.

It may be a helpful tool in the management of spasticity and other hypertonic muscle conditions.