Background Surgery for Ewing sarcoma involving acetabulum in children is challenging. Considering the intrinsic structure of immature pelvis, trans-acetabular osteotomy through triradiate cartilage might be applied. The study was to describe the surgical technique and function outcomes of trans-acetabular osteotomy through triradiate cartilage and reconstruction with customized, 3D-printed prosthesis. Methods Two children with periacetabular ES were admitted to our hospital. The pre-operative imaging showed the triradiate cartilage was not penetrated or wholly affected by tumor. After neoadjuvant chemotherapy, the tumor was excised by trans-acetabular osteotomy basing on “triradiate cartilage strategy” and the acetabulum was reconstructed with the customized, 3D-printed prosthesis. The prosthesis was designed in Mimics software basing on the images from CT, optimized by topology technique, and examined in FE model. After implantation, the oncological and functional outcomes were evaluated with radiography, CT, and MSTS score. Results The operation time and intra-operative blood loss in these two children were 3.5h, 2.5h and 300 ml, 600 ml, respectively. The postoperative specimen showed the tumor was en bloc removed with safe margin. In the latest follow-up (48 months and 24 months), both patients were free of disease and had satisfactory function according to MSTS score. The radiography indicated the prosthesis fit the defect well without loosening. Conclusion The customized, 3D-printed prosthesis could provide optimal reconstruction of pelvic ring and satisfactory hip function after trans-acetabular osteotomy in children. The translational potential of this article This study provides promising results of implantation of customized 3D printing prosthesis in children’s pelvic sarcoma, which may bring a new design method for orthopaedic implants.

Jackson et al., 1996). The main clinical manifestation is a progressive, painless enlargement of the jawbone, which is often diagnosed as a large tumor with cortical perforation and soft tissue invasion (Fregnani et al., 2010). Currently, surgical excision is a

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