Study design: Experimental, controlled study. Objective: To examine the effects of whole-body vibration (WBV) on bone mass and trabecular bone microstructure (TBMS) during the early stage in juvenile rats with spinal cord injury (SCI). Setting: Studied at the Kio University in Japan. Methods: Thirty-four 8-week-old male Wistar rats were divided into 3 groups: the SCI group, the sham-operation group (SHAM) and the SCI+WBV group. WBV started on the 8th day after SCI. After 1 or 2 weeks of WBV treatment, measurements of tissue mineral density, trabecular bone mineral content (BMC) and parameters of TBMS were obtained by scanning the proximal tibias with x-ray micro-computed tomography. Serum levels of osteocalcin (OC) and of tartrate-resistant acid phosphatase 5b (TRACP 5b) were measured with ELISA. Results: BMC, volume bone mineral density, bone volume (BV), BV fraction (BV/tissue volume) and connectivity density (Conn.D) of TBMS parameters were significantly higher in SCI+WBV rats than in SCI rats after 2-week WBV. The BMC and BV/TV of bone mass index correlated well with Conn.D, suggesting the preservation of Conn.D. induced by WBV. SCI+WBV rats showed a decrease in serum OC after 1-week WBV, but a quick recovery from that after 2-week WBV. There was no difference in serum TRACP 5b among the 3 groups throughout the experimental period. Conclusion: WBV treatment could attenuate the bone deterioration that occurs during the early stage in juvenile rats with SCI. In a clinic, this early WBV intervention may be an effective rehabilitation modality for preventing bone fragility in SCI patients. Spinal Cord (2016) 54, 597-603; doi:10.1038/sc.2015.220; published online 22 December 2015
INTRODUCTION
Osteoporosis is a well-known complication of spinal cord injury (SCI).The mechanism of bone loss by SCI is complex and is constituted by multiple factors involving mechanical, neurovascular, hormonal and metabolic factors. 1,2 Bone loss following SCI begins within the first 6 months after the injury, and stabilizes between 12 and 16 months. 3 Bone loss is especially prominent in sublesional bones such as the distal femur and proximal tibia. [4][5][6][7][8] In fact, bone mass in the distal femur and proximal tibia decreased by 51% and 70%, respectively, within 1 year after the injury in SCI patients. 6 These two bones were so fragile that even a weak physical impact could cause a fracture in SCI patients. 7,8 Therefore, the frequency of fracture in SCI patients was about twice as high as that of healthy people. 9 Edwards et al. 10 showed that in the femur and tibia of acute SCI patients trabecular bone mineral content (BMC) was reduced by 3.1-4.4% per month and volumetric bone mineral density (BMD) by 2.7-4.7% per month within 4 months after the injury. In addition, cortical BMC and volumetric BMD were noticeably reduced, and furthermore bone strength indices were decreased. 10 The incidence of SCI is higher in young people aged 15-24 years. 11 Children (aged 5-13 years) with