(P 272) OUTCOMES OF FOUR CASES OF TOTAL HIP ARTHROPLASTY (THA) WITH POROUS TANTALUM IMPLANT AFTER PARTIAL ACETABULAR RESECTION USING 3D PREOPERATIVE PLANNING FOR PELVIC BONE TUMORS

Objective: Introduction
Pelvic bone tumors around the acetabulum present significant challenges for accurate resection and reconstruction, often leading to postoperative functional impairments and complications. This report details four cases where 3D preoperative planning, using 3D printed bone models and mixed reality holograms, was employed for precise tumor resection and subsequent THA with porous tantalum implants. The approach involved collaboration between oncology and hip arthroplasty experts.

Methods: Subjects and Methods
Between 2021 and 2023, partial acetabular resection followed by THA was performed on four male patients with pelvic bone tumors around the acetabulum. The patients' histological diagnoses included: phosphaturic mesenchymal tumor, giant cell tumor, undifferentiated pleomorphic sarcoma (UPS), and solitary bone metastasis from renal cell carcinoma. The patients' ages ranged from 30 to 76 years, with an average age of 57 years. The average follow-up period was 16.5 months (range: 3-33 months). CT images were used to create 3D pelvic bone and tumor models with CAD software. Resection planes were planned using proprietary software developed at Osaka University (Bone Simulator). For two cases, 3D printed models of the pelvic bone and tumor were created; for the other two, mixed reality holograms of the pelvic bone, tumor, and resection planes were created using Holoeyes MD system. Navigation was employed in all cases for tumor resection, and THA reconstruction was performed using porous tantalum implant.

Results: Results
The average surgical time was 7 hours and 50 minutes (range: 7 hours 24 minutes to 8 hours 17 minutes), and the average blood loss was 1989 mL (range: 1405 mL to 3185 mL). Porous tantalum acetabular implants were used in three cases. Postoperative complications included one case of pulmonary embolism, managed with medication, and one case of sciatic nerve palsy, which recovered within six months. Postoperatively, three patients walked independently, and one required a cane. The mean MSTS score was 85% (range: 80%-93%), and the mean TESS score was 84% (range: 75%-89.4%). The UPS case experienced local recurrence and multiple metastases eight months postoperatively. The renal cell carcinoma case developed spinal metastasis at two months and sacral metastasis at six months postoperatively.
Discussion
The complex anatomical structure of the pelvis makes reconstruction after primary tumor resection around the acetabulum challenging. Reconstruction methods include THA, allograft implantation, arthrodesis, and hip transposition. However, each method has been associated with complications such as infection, aseptic loosening, delayed wound healing, leg length discrepancy, and dislocation, with no consensus on the best approach. In revision THA, porous tantalum implants have reported to provide mechanically stable hip joint structures to address bone defects. However, reports on using porous tantalum implants for acetabular reconstruction after pelvic tumor resection are scarce. In these cases, 3D preoperative planning enabled accurate partial preservation of the acetabulum, facilitating THA with porous tantalum implants. Short-term outcomes are favorable, but ongoing follow-up is necessary. The use of 3D printed models and mixed reality holograms proved valuable for intraoperative image sharing and interdisciplinary discussions.

Conclusion: Conclusion
This study demonstrates that 3D preoperative planning and porous tantalum implants for THA after pelvic bone tumor resection can yield favorable outcomes. These advanced planning tools enhance surgical precision and interdisciplinary collaboration, suggesting a promising approach for complex pelvic tumor resections. However, further long-term follow-up and studies are required to establish definitive conclusions.