The sub-axial ligaments of the spinal column help stabilize the vertebral column joints. The three main joints in the vertebral column stabilized by the sub-axial ligaments are the vertebral joints, costovertebral joints, and the sacroiliac joints. The vertebral joints consist of the intervertebral synovial and cartilaginous joints, both of which are the major components in forming a functional spinal unit. The costovertebral joints, only associated with the thoracic vertebrae, are a vital component in allowing adequate movement of the ribcage necessary for ventilation, yet can provide a sturdy encasement for the protection of the thoracic organs. The sacroiliac joints attach the sacrum to the left and right ilium.