Purpose The aim of the study was to develop an implant for fusion of the sacroiliac joint (SIJ) which, in contrast to known implant systems, can be used for isolated fusion of the SIJ as well as in combination with a lumbar instrumentation procedure or as an alternative to existing sacropelvic fixation (SPF) methods. Methods Following a comprehensive review of more than 200 high-resolution pelvic CT data sets, an implant body with high porosity and a large contact surface to the ilium and sacrum favoring integration was designed. Its shape was modeled based on the recess of the SIJ. A screw anchored in the ilium secures the position of the implant in the recess and allows connection to a lumbar instrumentation via an S1 screw. After receiving a detailed explanation and information about the novelty of the procedure, two patients with confirmed SIJ syndrome, who had undergone conservative treatment for more than 6 months without success, were operated on with a patient individual implant adapted to their anatomy. Results There were no intraoperative or postoperative complications. The postoperative CT and pelvic X-rays showed a good form fit of the implant body in the respective recess as well as correct positioning of the inserted screws. Conclusions The implant used first takes into account the special anatomy of the SIJ and also meets the requirements of a true arthrodesis of the joint. Clinical studies will now have to show whether the considerable theoretical advantages of the new implant system over existing SIJ implants and SPFs can be put into practice.