Mikhail Baryshnikov is on another tour. But his aging body isn’t keeping up. “In brief, he sells tickets on his reputation and performs whatever he’s commissioned from contemporary dance-makers, slight though the result might be. But how much can a choreographer ask of a vintage instrument in a fragile condition? Fit though Baryshnikov is, he has endured knee surgery many times. For his European tour, he’s had to abandon a tricky solo…”