Vertebrae are the 33 individual bones that interlock with each other to form the spinal column. The vertebrae are numbered and divided into regions: cervical, thoracic, lumbar, sacrum, and coccyx. Only the top 24 bones are moveable; the vertebrae of the sacrum and coccyx are fused.
When a person with a spinal cord injury retains some function below the level of the injury, they have an incomplete spinal cord injury. The American Spinal Injury Association (ASIA) established a grading system called the ASIA Impairment Scale to describe the severity of spinal cord injuries.