The spinal column can be identified in 5 parts, the caudal, sacral, lumbar, thoracic, and cervical vertebrae.
Each vertebrae has a spinous process which is longer or shorter depending on which vertebrae it is located on. Vertebrae also have four articular processes which assist in linking adjacent vertebrae together. The vertebral body is quite thick and links to adjacent vertebrae on a horizontal plain. A ring runs through each vertebrae housing the spinal cord. There is also an intervertebral disc between each vertebrae allowing forward and back along with side to side movement.
When the horse is not cared for physically he goes into mental imbalance. This is because he will drop his back due to underdeveloped muscles over his top line. This is caused by many things such as mental instability usually as a result of improper physical care. When the horse is in a state of flight with his back dropped, the spinous processes begin to rotate towards each other and over time the bones begin to rub. A result of this behavior or posture is spinal compression leading to kissing spines eventually fusing the bones which can lead to nerve damage and other painful sensations to the horse.
The erector spinous muscles become activated when the horse puts his head down which is in fact quite healthy for the horse. However, if the posture muscles are not well developed this has little affect on the opening of the spinous processes.
As a result poor muscular management in the horse, we start to see a hunters bump and compressed vertebrae where we begin to see exterior signs shown as lumps and bumps over the back and haunches. Compression is not limited to the haunches, however, it is most commonly visible in that area.
A training program is healthy when it incorporates healthy muscular development and it begins with the development of posture muscles. When the posture muscles are strong they open the vertebrae widening the spaces between the spinous processes and allowing joint fluid to replace itself. This allows the vertebral column to be very healthy and much less prone to injury.