High dose compressive loads attenuate bone mineral loss in humans with spinal cord injury

Abstract

Summary People with spinal cord injury (SCI) lose bone and muscle integrity after their injury. Early doses of stress, applied through electrically induced muscle contractions, preserved bone density at high-risk sites. Appropriately prescribed stress early after the injury may be an important consideration to prevent bone loss after SCI. Introduction Skeletal muscle force can deliver high compressive loads to bones of people with spinal cord injury (SCI). The effective osteogenic dose of load for the distal femur, a chief site of fracture, is unknown. The purpose of this study is to compare three doses of bone compressive loads at the distal femur in individuals with complete SCI who receive a novel stand training intervention. Methods Seven participants performed unilateral quadriceps stimulation in supported stance [150% body weight (BW) compressive load-"High Dose" while opposite leg received 40% BW-"Low Dose"]. Five participants stood passively without applying quadriceps electrical stimulation to either leg (40% BW load-"Low Dose"). Fifteen participants performed no standing (0% BW load-"Untrained") and 14 individuals without SCI provided normative data. Participants underwent bone mineral density (BMD) assessment between one and six times over a 3-year training protocol. Results BMD for the High Dose group significantly exceeded BMD for both the Low Dose and the Untrained groups (p<0.05). No significant difference existed between the Low Dose and Untrained groups (p≥0.05), indicating that BMD for participants performing passive stance did not differ from individuals who performed no standing. Highresolution CT imaging of one High Dose participant revealed 86% higher BMD and 67% higher trabecular width in the High Dose limb. Conclusion Over 3 years of training, 150% BWcompressive load in upright stance significantly attenuated BMD decline when compared to passive standing or to no standing. Highresolution CT indicated that trabecular architecture was preserved by the 150% BW dose of load. © International Osteoporosis Foundation and National Osteoporosis Foundation 2011.