In a sunlight-infused studio at the Baryshnikov Arts Center one recent afternoon, Lisa Bufano sat in a corner, attaching her prosthetics. Ms. Bufano, a 34-year-old performance artist whose legs are amputated just below the knee, worked methodically to attach what she called her “running legs,” a pair of coil-like springs. The task was made more difficult by the absence of Ms. Bufano’s fingers; they too were amputated in 1994, in one of 20 surgeries undertaken to save her life.