In a large skillet over medium heat, sauté the onion in the olive oil until translucent. Add the sausage and break apart with a fork. When the sausage is no longer pink, add the wine and cook for a few minutes. Add the radicchio and cook for 5-10 minutes, until wilted. Add salt and pepper to taste.
Add the pasta to the water and cook until al dente. Drain the pasta, retaining some of the cooking water. Add the pasta to the radicchio mixture. Mix well, adding some of the retained cooking water if it seems dry.