Background: Allograft-prosthesis composite reconstruction after periacetabular resections allows for bony union and internal repair, restoring bone stock for further revisions; the allograft-prosthesis composite can be shaped according to the pelvic resection to reconstruct the complex bone anatomy. Recently, endoprosthetic reconstruction has become one of the most frequently used options to restore large periacetabular bone defects. However, a prosthetic reconstruction impairs pelvic bone stock preservation and often takes a long time to manufacture. Allograft reconstructions, on the other hand, allow for bony union and internal repair, and they restore bone stock for further revisions. In addition, allografts are usually readily available and can be shaped according to the pelvic resection, fully restoring the complex bone anatomy. Pelvic biological reconstructions may have still a role, and to our knowledge, there are few long-term results of allograft-prosthesis composite reconstruction of the pelvis after periacetabular resections for bone tumors. Questions/purposes: (1) What is the cumulative incidence percentage of patients who experienced complications after reconstruction with allograft-prosthesis composites after resection of periacetabular tumors? (2) What was the functional result after surgical treatment as assessed by the Musculoskeletal Tumor Society (MSTS) score at a minimum of 2 years? (3) What was the survivorship of these reconstructions free from revision and graft removal at 15 years? Methods: Between February 1994 and April 2023, a total of 174 patients were treated at the university hospital of Florence for primary and secondary malignant or aggressive benign bone tumors of the pelvis with en bloc resection. Of treated patients, 51 underwent periacetabular resection and allograft-prosthesis composite reconstruction. We included in the study only patients with at least 24 months of follow-up or those who had complications earlier; thus 96% (49 of 51) of the patients had the required minimum follow-up and were included. Among the included patients, 88% (43 of 49) were available for a minimum follow-up of 24 months, whereas 12% (6) had < 24 months of follow-up but had complications earlier; thus, they were included for the analysis of complication-free survivorship. Seventy-eight percent (38) of patients were treated with a pelvic allograft combined with an acetabular cage, 16% (8) of patients received only a cemented cup, and 6% (3) of patients received a stemmed cementless cup. The mean ± SD follow-up time was 100 ± 77 months. The mean ± SD age at the time of reconstruction was 47 ± 17 years; 37% (18 of 49) of patients were female and 63% (31) were male. According to the Enneking and Dunham classification of pelvic resections, 39% (19) of patients had a Type I-II resection, 24% (12) had a Type II, 22% (11) had a Type II-III, 8% (4) had a Type I-II-III, 4% (2) had a Type I-II-IV, and 2% (1) had a Type I-II-III-IV. All patients had primary or secondary malignant or benign aggressive bone tumors: high-grade central chondrosarcoma (39% [19 of 49]), Ewing sarcoma (14% [7]), high-grade osteosarcoma (10% [5]), metastasis from carcinoma (10% [5]), dedifferentiated chondrosarcoma (10% [5]), peripheral low-grade chondrosarcoma (2% [1]), giant cell tumor of bone (2% [1]), osteoblastoma (2% [1]), hemangioendothelioma of bone (2% [1]), undifferentiated pleomorphic sarcoma of bone (2% [1]), malignant peripheral nerve sheath tumor of bone (2% [1]), radiation-induced sarcoma (2% [1]), or solitary plasmacytoma (2% [1]). The cumulative incidence of major complications, defined as surgical revision of any component of the reconstruction for mechanical complications and/or infections either surgically treated or not, and removal of the allograft as endpoints indicating failure, respectively, were estimated according to the competing-risk method. Complications were assessed through the revision of clinical charts. Death before the primary event of interest was considered a competing event. Comparisons of cumulative incidence curves across patient subgroups were performed with the Gray test. Normality of variables was assessed using the Shapiro-Wilk test, and heteroscedasticity was assessed using the Levene test. Accordingly, postoperative functional outcomes were compared across groups using a Welch t-test. Group means were reported in each plot. The relationship between functional score and length of follow-up was determined using a Pearson correlation coefficient. Significance was set at p < 0.05. The functional results were assessed using the MSTS score. The MSTS score was evaluated in patients with at least 2 years of follow-up in whom the pelvic allograft was retained at last clinical follow-up. Functional outcomes were assessed through the review of our institutional database. Results: The cumulative incidence of major complications was 24% (95% confidence interval [CI] 13% to 37%) at 5 years and 33% (95% CI 20% to 46%) at 10 and 15 years. The mean ± SD MSTS score was 23 ± 5, assessed 10 ± 6 years after the procedure. The cumulative incidence of graft removal was 8% (95% CI 3% to 18%) at 5 and 10 years and 12% (95% CI 4% to 24%) at 15 years. Conclusion: Allograft-prosthesis composite may represent an effective reconstructive option after periacetabular resection for primary bone tumors even in the era of 3D-printed implants; it still could have a role in patients with long life expectancy who are treated for tumors that were not managed with chemotherapy or radiotherapy and in whom the iliac wing is fully or partially preserved. Larger studies comparing periacetabular allograft-prosthesis composite with other reconstructive options such as modular and custom-made endoprostheses, as well as recycled autograft-prosthesis composites, are warranted to assess the potential benefits of one technique over the other. Level of Evidence: Level...

Introduction: A combined technique of In situ preparation (ISP) and adjuvant radiotherapy in a case of undifferentiated pleomorphic sarcoma (UPS) encasing the radial nerve was attempted successfully, which can be considered for the preservation of neurovascular structure close to soft-tissue sarcomas for a good functional and oncological outcome. Case Presentation: A 41-year-old female diagnosed with UPS of the left arm underwent, en bloc excision of the lesion along with the preservation of encased radial nerve using ISP followed by adjuvant radiotherapy. The patient has good functional outcome and a local recurrence free and overall survival of 5 years. Conclusion: We reported a case of UPS encasing the left radial nerve, an ISP technique and adjuvant radiotherapy were successfully attempted for attaining a good functional and oncological outcome.