Spina bifida is a birth defect where the spinal cord does not close completely during pregnancy. There are three main types Lian has the most severe form of spina bifida which is called Myelomeningocele:

The spinal cord and nerves protrude through the gap in the spine, forming a sac on the back. 

This can lead to significant neurological disabilities, such as paralysis, loss of bladder and bowel control, and hydrocephalus (excess fluid in the brain). Lian also had a shunt placed to drain the excess fluid in his brian.
Picture of Lian working hard today in physical therapy.