Effects of transcutaneous electrical nerve stimulation and body-weight-supported treadmill training on motor functions in children with spastic cerebral palsy

Abstract

Transcutaneous electrical nerve stimulation (TENS) and body-weight-supported treadmill training (BWS-TT) have been separately proven to reduce spasticity and/or enhance gait functions in adults with neurological disorders. The extent to which a combination of such treatment approaches could reduce spasticity and facilitate gait performance in children with cerebral palsy (CP) has not been investigated. Since children are believed to have greater neuronal plasticity, we hypothesized that (1) TENS and/or TENS+BWS-TT would reduce spasticity more than placebo-TENS; and that (2) combining TENS with BWS-TT would further improve muscle function and walking performance than TENS alone in children with CP. This study was a prospective, randomized, placebo-controlled clinical trial. Sixty-three children diagnosed with spastic CP were recruited from 6 special schools and 61 completed the study. Children with "mild", "moderate", or "severe" levels of ankle plantarflexor spasticity, as defined by the composite spasticity scale (CSS) score, were randomly allocated to 1 of 3 groups receiving TENS (n = 20), placebo-TENS (n = 21), or TENS+BWS-TT (n = 20). They were 6 to 15 years old, 32 were females and 29 males, 54 had spastic diplegia and 7 had spastic hemiplegia. All children received similar conventional therapy programs. In the TENS group, low-intensity TENS was applied via surface electrodes connected to a portable TENS stimulator to the skin overlying the common peroneal nerve. Continuous stimulation (0.125 msec square pulses, 100 Hz, intensity at 2 times the sensory threshold) was applied for 60 minutes, once a day, for 5 days a week for 3 weeks. In the placebo-TENS group, the same device and stimulation parameters as those in the TENS group were used with the circuit inside the device disconnected. In the TENS+BWS-TT group, TENS was delivered for 60 minutes, followed by 20 to 30 minutes of BWS-TT according to the walking tolerance and progression of each child. Outcome measurements included: (1) spasticity of the ankle plantarflexors assessed by CSS and stretch reflex as a function of maximum M response (SR/M), (2) muscle function assessed by maximum isometric voluntary contraction (MIVC) and EMG co-contraction ratios of ankle dorsiflexor and plantarflexor muscles, and (3) walking performance evaluated by walking speed and energy cost (physiological cost index, PCI) during a 6-minute walk test. These measurements were recorded before treatment (T0), and after 1 week (T1), 2 weeks (T2), and 3 weeks of treatment (T3), to examine the effects and time course of TENS, placebo-TENS and TENS+BWS-TT. The results showed no significant differences among the groups before treatment. When compared with placebo-TENS, both TENS and TENS+BWS-TT produced a significant % decrease of CSS scores, respectively, after 3 and 2 weeks of treatment (p < 0.006). Interestingly, only TENS+BWS-TT but not TENS alone produced a significant % decrease of SR/M area ratio and of dorsiflexion co-contraction ratio, and a significant % increase of dorsiflexion torque after 3 weeks of treatment (p < 0.006). However, none of the interventions produced a significant change in plantarflexion torque or co-contraction ratio after 3 weeks of treatment. Despite no significant change of walking speed being noted among the groups, 3 weeks of TENS+BWS-TT produced a significant % decrease of PCI (p < 0.006). This may partly be explained by a significant % decrease of the heart rate change (HRwalk - HRrest) after 3 weeks of TENS+BSW-TT. In conclusion, both TENS and TENS+BWS-TT are feasible treatment protocols for children with spastic CP in the school setting. Both treatments significantly reduced clinical spasticity after being administered for only 2-3 weeks. However, voluntary contraction of ankle dorsiflexors, hyperactive SR of plantarflexors and energy cost of walking were improved only when the 3 weeks TENS were combined with BWS-TT. These findings supported our hypothesis that combining TENS with specific locomotive training was needed to bring about functional gain. This is the first randomized controlled trial which demonstrated that 15 sessions of combined TENS+BWS-TT treatment were superior to TENS alone in reducing spasticity and in enhancing voluntary muscle function and walking performance in children with spastic CP. This treatment strategy has the added benefits of being non-invasive, low cost, and without the side-effects often associated with drug intake or surgery such as dorsal rhizotomy. The extent to which 3 weeks of BWS-TT alone would bring significant improvement in muscle and mobility function requires further investigation.