The invention concerns a method for manufacturing a prosthesis (11) for afractured longbone of a patient, the method comprising the steps of: A) providing datarepresentative of thefractured long bone, the fractured long bone comprising a diaphyseal fragment(2) comprisinga medullary cavity (8)； B) based on said data, designing the prosthesisspecifically to thepatient, the prosthesis comprising a stem part (12) configured to be insertedinto themedullary cavity, step B) comprising: a sub-step of choosing, specifically tothe patient, acontact zone (40) of the medullary cavity onto which a respective chosenmechanical stress isplanned to be applied by the stem part, and a sub-step of designing the stempart so that thestem part may be inserted into the medullary cavity and thus apply the chosenmechanicalstress to said contact zone； and C) manufacturing the prosthesis designed atstep B).
