Effect of high-frequency, low-magnitude vibration on bone and muscle in children with cerebral palsy.
BACKGROUND
Children with cerebral palsy (CP) have decreased strength, low bone mass, and an increased propensity to fracture. High-frequency, low-magnitude vibration might provide a noninvasive, nonpharmacologic, home-based treatment for these musculoskeletal deficits. The purpose of this study was to examine the effects of this intervention on bone and muscle in children with CP.


METHODS
Thirty-one children with CP ages 6 to 12 years (mean 9.4, SD 1.4) stood on a vibrating platform (30 Hz, 0.3 g peak acceleration) at home for 10 min/d for 6 months and on the floor without the platform for another 6 months. The order of vibration and standing was randomized, and outcomes were measured at 0, 6, and 12 months. The outcome measures included computed tomography measurements of vertebral cancellous bone density (CBD) and cross-sectional area, CBD of the proximal tibia, geometric properties of the tibial diaphysis, and dynamometer measurements of plantarflexor strength. They were assessed using mixed model linear regression and Pearson correlation.


RESULTS
The main difference between vibration and standing was that there was a greater increase in the cortical bone properties (cortical bone area and moments of inertia) during the vibration period (all P's ≤ 0.03). There was no difference in cancellous bone or muscle between vibration and standing (all P's > 0.10) and no correlation between compliance and outcome (all r's < 0.27; all P's > 0.15). The results did not depend on the order of treatment (P > 0.43) and were similar for children in gross motor function classification system (GMFCS) 1 to 2 and GMFCS 3 to 4.


CONCLUSIONS
The primary benefit of the vibration intervention in children with CP was to the cortical bone in the appendicular skeleton. Increased cortical bone area and the structural (strength) properties could translate into a decreased risk of long bone fractures in some patients. More research is needed to corroborate these findings, to elucidate the mechanisms of the intervention, and to determine the most effective age and duration of the treatment.


LEVEL OF EVIDENCE
Level II, prospective randomized cross-over study.