Slip fells action heroine

Jaimie Alexander suffered a severe back injury on the set of the Thor sequel “The Dark World.” “It was raining, it was dark outside, it was like 5 in the morning — and I went down a metal staircase and slipped and slipped a disc in my thoracic spine and chipped 11 of my vertebrae,” Alexander told us about the September incident at a screening for the Twilight saga’s “Breaking Dawn: Part 2” on Thursday at Landmark Sunshine Cinema. “I knocked my left shoulder out of place and tore my rhomboid on my right side . . . It took me out of filming for a month.” Alexander, who plays Sif in the action epic staring Chris Hemsworth and Natalie Portman, is back on set. “I heal really fast,” she continued. “Everyone thinks it’s really funny to tease me about staircases now that I fell down one . . . I’m walking in heels again though, so that’s a good sign.” The actress, who has just started dating “Twilight” star Peter Facinelli, will also be in 2013’s “The Last Stand,” starring Arnold Schwarzenegger.