When Ponyboy and his brothers visit the hospital to see Johnny, the doctor explains Johnny's condition to them. The doctor tells the boys that Johnny is in critical condition and has a broken back from where the piece of timber fell on him. The doctor then tells the Curtis brothers that even if Johnny recovers, he will be crippled for the rest of his life. This news comes as a shock to Ponyboy, who begins to tremble after listening to the doctor's explanation. Ponyboy then begins to image what life would be like for Johnny as a disabled person. Ponyboy reasons that Johnny would hate life because he would not be able to participate in sports or rumbles with the gang, and essentially be forced to stay inside his dysfunctional home all day. However, Johnny ends up dying from his injuries and does not have to spend the rest of his life in a wheelchair.
I assume that you are talking about the first time that the doctor talks about Johnny. This is the time where he is talking to Pony and his brothers, Soda and Darry, telling them about Dally and Pony.
At this point, the doctor says first of all that he does not know if Johnny is going to live. He keeps talking about if Johnny lives. He says that Johnny has broken his back. He says that if Johnny does not die he will be crippled for the rest of his life because his back is broken.
He says that Johnny might or may not live.