How Kaley Cuoco's 2010 horseback riding accident almost ended 'The Big Bang Theory'

The Big Bang Theory almost ended a lot sooner than it did.

The Chuck Lorre-created sitcom, which began in 2007 and lasted for 12 seasons, came close to losing one of its stars in Sept. 2010, when avid equestrian Kaley Cuoco was injured in a brutal accident during a lesson, according to People, which cites an excerpt from Jessica Radloff's new oral history, The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series, obtained by Vanity Fair. It happened as the actress fell off the horse she was riding, only for the horse to step on her left leg.

Cuoco was immediately taken to the hospital, where she was presented with a scary choice.

"Before I went into surgery, they made me sign something that said, 'We don't know until we get in there and see this leg, and it could come out that you don't have it anymore,'" Cuoco said. "That wasn't the case, obviously, but I had to sign something that said, 'OK, you can.'"

Lorre recalled the incident as "the darkest, most frightening time in all twelve years" of the Emmy-winning CBS sitcom, and one that could have ended it.

The Big Bang Theory co-star Johnny Galecki, who Cuoco dated for almost two years between 2007 and 2009, called the scary news "devastating to hear."

Lorre credited Dr. Stephen Lombardo, of the Cedars-Sinai Kerlan-Jobe Institute, whom he ran into at a truly serendipitous time, with agreeing to help his leading lady — pronto. She was taken into surgery within two hours.

Despite doctors' predictions that she wouldn't walk for months, Cuoco was able to leave the hospital in a walking boot after two weeks.

"Everything ended up fine, and I was up and working a week later, but the doctors acted like I was never going to walk again," Cuoco said. "It's still too much for me to go into, and it sounded way worse than it was. And of course it was spiraling and everyone was freaking out, which I get. It scared people."

In fact, Galecki said he "shed tears in my garage" after seeing Cuoco for the first time following the accident.

The month following her injury, Cuoco herself was well enough to appear on The Ellen DeGeneres Show, where she explained that she'd heard her bones breaking, but at the time she was hoping the cracking was from the horse stepping on leaves, not her leg.

The new book also includes revelations about the other actresses who came close to landing Cuoco's role of Penny; the exact scene where Cuoco and Galecki fell in love and the reason they eventually split; Cuoco's regrets about her drastic haircut before Season 8; and the way co-star Jim Parsons blindsided the cast when he decided to leave the popular show, which resulted in the end of it.