* Two snowboarders crash early in competition
* Course not to blame, says IOC (adds Moioli injury in para 11)
ROSA KHUTOR, Russia, Feb 16 (Reuters) - Two of the first six riders in Sunday's opening snowboard cross seeding run were taken away on stretchers after falling heavily, causing concern a day after Russian freestyle skier Maria Komissarova was seriously injured on the same course.
Komissarova underwent more than six hours of spinal surgery at Krasnaya Polyana Hospital Number 8 on Saturday after breaking her back in a crash during training for the women's ski cross at the Rosa Khutor Extreme Park.
The course for the snowboarding event has some different sections but many of the same jumps, twists and turns.
Norwegian Helene Olafsen was the first rider out and after one jump turned 180 degrees before landing on her back and shoulder.
There was a lengthy delay as she was tended to on the course but she appeared to be conscious as she was stretchered off the slope.
"Helene has torn the anterior cruciate ligament in her left knee," Norway Olympic team doctor Ellen Moen said in a new release. She also has an injury to the ligament on the inside of the same knee, and a meniscus injury.
"She will most likely have to have an operation on the knee, but we cannot say anything more about it yet."
American Jacqueline Hernandez, who went out sixth, was the second faller, hitting the slope with a thud as she tried to land backwards and appearing to lose consciousness as she smashed her head into the snow.
Again there was a delay as she received medical treatment but she had also recovered consciousness before she was taken away on the stretcher.
The U.S. team later said Hernandez had been treated in the medical tent where they ascertained she had suffered a concussion. She was withdrawn from the competition.
Italy's Michela Moioli later ruptured a cruciate ligament in her knee after a fall in the final and will return home to undergo surgery, the Italian Olympic Committee said on their website.
The International Olympic Committee said the courses had been approved by the federations, who are responsible for their respective fields of play.
"I know they are very happy with it," IOC spokesman Mark Adams told reporters.
He said he had just been informed of the two incidents in the snowboarding competition but said there was "no huge cause for concern," and they were unrelated to the Komissarova accident.
"The accident was in an individual practice. She (Komissarova) was actually in training by herself when the accident happened. So it is not actually the format or the course that is necessarily the problem.
"They (courses) did not appear to have any difference from Vancouver (2010 Olympics). The athletes are happy with the course," he said.
Despite the two heavy falls on Sunday morning, American boarder Faye Gulini echoed Adams's view that there was nothing wrong with the course.
"This is a great course, but it is intimidating," she said after finishing fourth in the final.
"We don't usually have courses that have jumps this big and it's so much fun. But some girls don't have this capability of hitting these huge jumps.
"This course is safe. It has big features which are intimidating looking, but it's built right. So if you give this course all the speed you can it's gonna work. If you do everything right you will be on your feet.
"For a lot of people, it was a mental thing." (Additional reporting by Karolos Grohmann and Philip O'Connor, Editing by Peter Rutherford)