In our rapidly changing world, we are often encouraged to treat our bodies as objects of constant improvement by means of various facilities and innovations. As part of this “Promethean tendency,” the present-day alliance between medicine and technology has opened up a new perspective on the ill and disabled body, by providing access to sophisticated prosthetics that are increasingly seen as ideal remedies. These devices allow patients to benefit from previously unimaginable treatments and inestimable scientific advances, yet they also create new forms of dependency that go beyond simply forming a habit. They are part of a complex process which results in the construction of a body full of paradoxes and whose effects go beyond the subject's image construction. Based on the case of Mathilde, a little girl with a partial arm agenesis, the author traces some elements of the psychic process of constructing a body: from a congenital malformation towards a body “supplemented” by a prosthesis.