The invention concerns a method for manufacturing a prosthesis (11) for a fractured long bone of a patient, the method comprising the steps of: A) providing data representative of the fractured long bone, the fractured long bone comprising a diaphyseal fragment (2) comprising a medullary cavity (8)； B) based on said data, designing the prosthesis specifically to the patient, the prosthesis comprising a stem part (12) configured to be inserted into the medullary cavity, step B) comprising: a sub-step of choosing, specifically to the patient, a contact zone (40) of the medullary cavity onto which a respective chosen mechanical stress is planned to be applied by the stem part, and a sub-step of designing the stem part so that the stem part may be inserted into the medullary cavity and thus apply the chosen mechanical stress to said contact zone； and C) manufacturing the prosthesis designed at step B).
