A comprehensive study of long-term skeletal changes after spinal cord injury in adult rats

Abstract

Spinal cord injury (SCI)-induced bone loss represents the most severe osteoporosis with no effective treatment. Past animal studies have focused primarily on long bones at the acute stage using adolescent rodents. To mimic chronic SCI in human patients, we performed a comprehensive analysis of long-term structural and mechanical changes in axial and appendicular bones in adult rats after SCI. In this experiment, 4-month-old Fischer 344 male rats received a clinically relevant T13 contusion injury. Sixteen weeks later, sublesional femurs, tibiae, and L4 vertebrae, supralesional humeri, and blood were collected from these rats and additional non-surgery rats for micro-computed tomography (µCT), micro-finite element, histology, and serum biochemical analyses. At trabecular sites, extreme losses of bone structure and mechanical competence were detected in the metaphysis of sublesional long bones after SCI, while the subchondral part of the same bones showed much milder damage. Marked reductions in bone mass and strength were also observed in sublesional L4 vertebrae but not in supralesional humeri. At cortical sites, SCI induced structural and strength damage in both sub- and supralesional long bones. These changes were accompanied by diminished osteoblast number and activity and increased osteoclast number and activity. Taken together, our study revealed site-specific effects of SCI on bone and demonstrated sustained inhibition of bone formation and elevation of bone resorption at the chronic stage of SCI.

Spinal cord injury: long-term bone loss

Spinal cord injury (SCI) in rats has a chronic detrimental effect on skeletal structure with severe bone loss in the lower half of the body. Injury to the spinal cord can cause multiple long-term problems including severe osteoporosis, for which there is no effective treatment. Ling Qin at the University of Pennsylvania, USA, and co-workers conducted a long-term study of chronic SCI in Fischer 344 rats. They found a low level of bone formation and a high level of bone resorption at 16 weeks following SCI. This resulted in considerable bone loss and structural damage in the rat legs, particularly in spongy bone. The vertebrae below the SCI site also suffered bone loss, with more limited damage in the upper half of the body. The team recommend anabolic treatments that stimulate new bone formation to promote bone health in SCI patients.

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