A method for manufacturing a prosthesis for a fractured long bone of a patient, the method comprising the steps of: A) providing data representative of the fractured long bone of the patient, the fractured long bone comprising a diaphyseal fragment comprising a medullary cavity; B) based on the data provided at step A), designing the prosthesis specifically to the patient, the prosthesis comprising a stem part configured to be inserted into the medullary cavity for securing the stem part to the diaphyseal fragment, step B) comprising: - a sub-step of choosing, specifically to the patient, at least one contact zone of the medullary cavity onto which a respective chosen mechanical stress is planned to be applied by the stem part, when the stem part is inserted into the medullary cavity 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 at least one contact zone; and C) manufacturing the prosthesis including the stem part designed at step B); characterized in that step B) comprises the further sub-step of, based on the data provided at step A), designing the stem part so that the stem part comprises, specifically to the patient: - a coverable diaphyseal portion, configured to be covered by the diaphyseal fragment when the stem part is secured to the diaphyseal fragment, whereas the rest of the stem part is left uncovered by the diaphyseal fragment; and - a first visible mark, visually delimiting the coverable diaphyseal portion from the rest of the stem part. A) providing data representative of the fractured long bone of the patient, the fractured long bone comprising a diaphyseal fragment comprising a medullary cavity; B) based on the data provided at step A), designing the prosthesis specifically to the patient, the prosthesis comprising a stem part configured to be inserted into the medullary cavity for securing the stem part to the diaphyseal fragment, step B) comprising: - a sub-step of choosing, specifically to the patient, at least one contact zone of the medullary cavity onto which a respective chosen mechanical stress is planned to be applied by the stem part, when the stem part is inserted into the medullary cavity 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 at least one contact zone; and - a sub-step of choosing, specifically to the patient, at least one contact zone of the medullary cavity onto which a respective chosen mechanical stress is planned to be applied by the stem part, when the stem part is inserted into the medullary cavity 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 at least one contact zone; and C) manufacturing the prosthesis including the stem part designed at step B); characterized in that step B) comprises the further sub-step of, based on the data provided at step A), designing the stem part so that the stem part comprises, specifically to the patient: - a coverable diaphyseal portion, configured to be covered by the diaphyseal fragment when the stem part is secured to the diaphyseal fragment, whereas the rest of the stem part is left uncovered by the diaphyseal fragment; and - a first visible mark, visually delimiting the coverable diaphyseal portion from the rest of the stem part. - a coverable diaphyseal portion, configured to be covered by the diaphyseal fragment when the stem part is secured to the diaphyseal fragment, whereas the rest of the stem part is left uncovered by the diaphyseal fragment; and - a first visible mark, visually delimiting the coverable diaphyseal portion from the rest of the stem part.