Changes in bone mass, bone structure, bone biomechanical properties, and bone metabolism after spinal cord injury: a 6-month longitudinal study in growing rats.

Spinal cord injury (SCI) results in a great decline in bone mineral density (BMD) and deterioration of bone microarchitecture. The objective of this study was to investigate the time course of the changes in BMD, microarchitecture, biomechanical properties, and bone turnover in male growing rats following SCI. Sixty male growing Sprague-Dawley rats, 6 weeks of age, were randomly divided into SCI (lower thoracic cord transection) and sham-operated groups, and bone tissues and blood samples were examined at 3 weeks, 6 weeks, and 6 months after surgery. SCI rats had low bone weight (wet, dry, and ash weight) and BMD of the femora, tibiae, and third lumbar vertebrae at all time points compared to sham rats, while in forelimbs, there was a decrease of dry and ash weight compared to sham rats only at 3 weeks but not BMD. Bone microarchitecture and trabecular connectivity were deteriorated in SCI rats and remained so after. Bone formation rate and serum osteocalcin level in SCI rats were significantly increased 3 weeks after SCI surgery. However, eroded surface/bone surface and serum N-terminal telopeptide of type I collagen level remained elevated from 3 weeks to 6 months. In addition, SCI rats showed poor biomechanical properties in the proximal tibiae and femora but not in the humeri. In conclusion, SCI causes profound BMD loss, disturbances in bone microarchitecture, decreased mechanical strength in the lower extremity and lumbar spine, and high bone turnover. These findings will allow better understanding of osteoporosis following SCI.