Ralph Macchio said via Twitter he hopes a ruptured cyst on the back of his knee doesn't keep him from performing on "Dancing with the Stars." The former teen idol and his professional dance partner, Karina Smirnoff, are one of the last five couples left on the show this season. Each couple is to perform two routines Monday night, People.com said. "Have missed days of rehearsal this week," Macchio said in a Twitter message Monday. "Had a ruptured cyst on the back of my knee causing acute pain. Hoping to be able to perform tonight!"