William Forsythe is usually called a radical in that he’s long since abandoned ballet’s classical harmonies and theatre’s linear conventions. Yet for all his extremities, the choreographer’s purpose remains intensely humane, albeit with painfully disruptive means.

You see it clear in You Made Me a Monster, a 50-minute choreographic installation that opened Sadler’s Wells’s two-and-a-bit-week retrospective of his work. The audience don’t sit in their seats, nor are they passive observers.

Instead they are on stage taking part in a Blue Peter-like game of paper sculpture. On 13 tables are piles of brown card, and you soon recognise they’re those flat-pack paper skeleton kits. Only instead of assembling the femurs and fibulas into human harmony, we’re asked to twist and contort them into osteo disarray.

Then three dancers hurtle around the space, their bodies wracked with palsy, their cries electronically distorted. Then comes the realisation, revealed in a projected text, that Forsythe’s young wife died of cancer. After her death he assembled a paper skeleton without the instructions. The result was a model of grief, which the audience unknowingly recreate.

With 18 writhing dancers and a relentless dialogue of distress, Decreation is no easier. It’s like watching magnets spongily repel each other only to snap shut, then twist and struggle to separate. Forsythe is an emotional lodestone of the bleakest kind.
Focus on Forsythe until 10 May. 0844 412 4300. www.sadlerswells.com