Brack was chatting to his wife after the crash despite his injuries

The former Indy Racing League (IRL) champion locked wheels with Tomas Scheckter, somersaulting his car into fencing and down the track.

Doctors at the Parkland Hospital in Dallas repaired a spinal fracture and fused three vertebrae on Monday.

"Kenny's spine is stable, and he's moving his legs and toes," said Dr. Kevin Morrill.

"We will continue to watch him closely over the next couple of days. Kenny is a world-class athlete, and his physical conditioning will really aid him in this situation."

Brack earlier had successful surgery on his broken thigh and broken ankles.

IRL officials said Brack, who drives for Team Rahal, was awake and alert while he was tended to in the infield care centre after the crash.

"Brack was cracking jokes with his wife Anita while in the care centre," said Steve Dickson, manager of Team Rahal.

Brazil's Gil de Ferran won the race for Penske Racing, which was shortened following Brack's accident, and immediately confirmed his retirement.

De Ferran calls time Dixon claims IRL title

De Ferran, who won this year's Indianapolis 500, was subdued at the post-race news conference.

"Obviously, my thoughts and prayers are with Kenny," he said.

Scott Dixon won the IRL title with 507 points, with De Ferran in runner-up spot and Penske team-mate Helio Castroneves in third.