Method for manufacturing an auxiliary device suitable for the manufacture of a patient customized implant comprising the steps of: 1) obtaining 3D image data, preferably a CT, of a defect site of a patient's anatomy; 2) generating a computer model of the defect site based on the 3D image data obtained in step 1 and 3D generic reference data and by using image processing techniques; 3) virtually reconstructing the defect site and designing the patient customized implant; characterized by the steps of: 4) generating a computer template by using the computer model generated in step 2, wherein the computer template (i) covers the virtually reconstructed defect site with an overlay which defines the shape and size of a peripheral projection of the auxiliary device that is slightly bigger than the virtually reconstructed defect site and which is suitable to be fitted to an unaffected region in the area of the defect site; and (ii) comprises a recess positioned on a surface that is directed towards the virtually reconstructed defect site and wherein the recess spans the virtually reconstructed defect site and wherein the size of the recess is larger than the size of the virtually reconstructed defect site so as to encompass the shape of the defect site in order to shape and size an implant; and 5) manufacturing the auxiliary device specified by the computer template generated in step 4 using 3D printing. 1) obtaining 3D image data, preferably a CT, of a defect site of a patient's anatomy; 2) generating a computer model of the defect site based on the 3D image data obtained in step 1 and 3D generic reference data and by using image processing techniques; 3) virtually reconstructing the defect site and designing the patient customized implant; characterized by the steps of: 4) generating a computer template by using the computer model generated in step 2, wherein the computer template (i) covers the virtually reconstructed defect site with an overlay which defines the shape and size of a peripheral projection of the auxiliary device that is slightly bigger than the virtually reconstructed defect site and which is suitable to be fitted to an unaffected region in the area of the defect site; and (ii) comprises a recess positioned on a surface that is directed towards the virtually reconstructed defect site and wherein the recess spans the virtually reconstructed defect site and wherein the size of the recess is larger than the size of the virtually reconstructed defect site so as to encompass the shape of the defect site in order to shape and size an implant; and (i) covers the virtually reconstructed defect site with an overlay which defines the shape and size of a peripheral projection of the auxiliary device that is slightly bigger than the virtually reconstructed defect site and which is suitable to be fitted to an unaffected region in the area of the defect site; and (ii) comprises a recess positioned on a surface that is directed towards the virtually reconstructed defect site and wherein the recess spans the virtually reconstructed defect site and wherein the size of the recess is larger than the size of the virtually reconstructed defect site so as to encompass the shape of the defect site in order to shape and size an implant; and 5) manufacturing the auxiliary device specified by the computer template generated in step 4 using 3D printing.