Outcomes of pelvis resections and reconstructions using 3D printed cutting guides referencing the acetabulum

Background Oncologic resections and reconstructions of the pelvis are among the most challenging procedures in orthopedic surgery due to complex anatomy, tumor variability, and the need for precise margins. Patient-specific instrumentation (PSI) created with 3D printing has emerged as a promising solution, but accurate intraoperative referencing remains difficult. This study evaluates the use of novel acetabular-referencing PSI cutting guides for pelvic tumor resections and reconstructions. Methods Five patients (mean age 57.2 years) underwent pelvic resections with acetabular-referencing PSI between 2019 and 2023. Each guide incorporated a hemispherical feature seating within the acetabulum after femoral head removal. Postoperative CT reconstructions were compared with preoperative plans to assess resection accuracy, implant alignment, operative time, and margin status. Results All patients achieved negative gross margins; two had microscopically positive margins (one planned). Mean operative time was 8hours 52minutes, including two complex procedures. Mean deviations were 8.32mm for center of rotation (CoR) and 7.37mm for center of gravity (CoG). Directional CoR deviations averaged 2.62mm anteroposteriorly, 6.30mm mediolaterally, and 3.92mm superoinferiorly. Angular deviations averaged 1.88° in anteversion and –2.54° in inclination. All implants were positioned within or near accepted thresholds for pelvic reconstruction accuracy. Conclusions Acetabular-referencing PSI enabled reproducible guide placement and accurate osteotomies in complex pelvic resections without increasing operative time. This technique offers a reliable alternative to surface-contoured guides and may enhance precision in oncologic reconstruction by mitigating challenges of intraoperative interfacing. Larger studies with long-term follow-up are needed to confirm functional outcomes and implant survivorship.