They were nearing the end of their belly-dance themed salsa when the injury hit, bringing tears from Katherine as they messed up the final move. However, the judges reassured her they'd seen enough and awarded 27 out of 30 points, with Bruno saying: "You unleashed the harlot, which is good to see - handle with extreme care, because it bites - so don't worry about what happened, because it happens to everybody. Up to that point it was absolutely wonderful darling, so don't beat yourself up."
And Len Goodman added: "I just wrote, 'Katherine the great, the world's wonder woman'. You absolutely came out and gave that 100%."
Watch it here - it looks like Mark caught her leg as he turned and threw them both off balance, and heading up the stairs you can see she's taking them gingerly. Aside from that though - this was one totally wicked Beyonce-esque salsa! Forget the ballroom, Kath's next move should be Streetdance, the next sequel!
Katherine subsequently tweeted her concerned fans the following message: "Thank you for all your concerned tweets ... I'm with the doctor, he says it was a reflectorical spasm in my lower back."
Kama had earlier performed a quickstep, which scored 29 out of 30, giving them a combined score of 56. I saw the little stumble there, like Len, but really, her characterization and movement every week has been spot on.
In one of the closest semis ever, it was Derek Hough and Mania Menounos who missed out on the final, with William Levy & Cheryl Burke and Daniel Driver & Peta Murgatroyd going through with Team Kama.