Assessing the effect of spinal cord injury severity on the mechanical properties of the hind limb bones of experimental rats

Spinal cord injuries are often accompanied by osteoporosis, which complicates rehabilitation. The effect of injury severity on changes in bone strength properties is poorly understood. Therefore, the aim of the present study was to assess changes in bone mechanical properties in the diaphyseal region after spinal cord injury of different severity (contusion and total spinal cord injury). The study was conducted on non-linear rats weighing 180-200 g. Animal housing and experimental procedures were carried out in compliance with bioethical norms. Complete spinal cord injury was simulated by transection of the spinal cord at the Th8-Th9 level. Contusion trauma to the spinal cord was inflicted at the Th8-Th9 level according to a modified technique by A. R. Allen. Animals were removed from the experiment on the 30th day, after which the bones (tibia and femur) were extracted. Geometric, volumetric and mass characteristics were determined for each bone, and three-point bending tests were performed. The results showed that spinal cord injury in experimental rats resulted in a loss of strength in the femur and tibia. In the case of contusion injury, the decrease in hind limb strength was more pronounced in rats (21 % in the tibia and 27 % in the femur) than in total spinal cord injury (21 % in the tibia and 19 % in the femur). At the same time, the density and Young's modulus of the tibia and femur did not significantly change after total and contusion spinal cord injury in rats. On the basis of the results obtained, the authors hypothesized that in the process of immobilization after spinal cord injury of different severity, the bone microarchitecture of the experimental animals was changed. It is suggested that it is the changes in the microarchitecture that lead to significant changes in bone strength.