Purpose: Periprosthetic fractures of a tumor prosthesis are rare but have difficulties in achieving sound fixation because of the poor bone quality, which increases the risk of loosening or re-fracture, even after bone union. A cortical strut onlay allograft was adopted for peri-prosthetic fractures after hip arthroplasty into the periprosthetic fracture of a tumor prosthesis, assuming that it would assist in firm fixation, shorten the time to union, and increase the bone stock, thereby, lower the chance of loosening and re-fracture. Materials and Methods: This study reviewed 27 patients (30 cases) of periprosthetic fracture of tumor prosthesis. Sixteen cases (allograft group) had augmentation with an onlay allograft, while 14 cases (conventional group) had internal fixation or conservative treatment.The following were assessed; mode of periprosthetic fracture, difference in the time to union between a strut cortical onlay allograft and without it, and survival of prosthesis, complication, and functional outcome between the two groups. Results: According to the unified classification system (UCS), 21 cases were type B (70.0%; B1, 14; B2, 1; B3, 6) and 9 cases were type C.The five-, 10-year survival of the 30 reconstructions by Kaplan–Meier plot was 84.5%±4.18% and 42.2%±7.83%, respectively. The average time to bone union of the entire cohort was 5.1 months (range, 2.0–11.2 months). The allograft group (3.5 months) showed a shorter period for union than the conventional group (7.2 months) (p<0.0001). All four cases of major complications occurred in the conventional group. Two cases with loosening and anterior angulation were treated with a change of prosthesis, and another with infection underwent amputation. The remaining case with loosening had conservative management. At the final follow-up, the average Musculosketal Tumor Society score of the allograft group (26.1) was better than that of the conventional group (20.9). Conclusion Bone union in periprosthetic fractures of a tumor prosthesis can be achieved, but the minimization of complications is important. An onlay allograft facilitates firm fixation and increases the bone stock with a shortened time to union. This simple method can minimize the risk of loosening, joint contracture, and re-fracture.

Purpose: Liposarcoma is a mesenchymal neoplasm and comprise 20%–30% of all soft tissue sarcomas, accounting for 1% of all malignancies. This study documented the clinical manifestation and oncological outcomes of dedifferentiated liposarcoma (DDLPS). Materials and Methods: Eleven patients were diagnosed and treated for DDLPS between January 2013 and December 2020. The age, gender, symptom onset, tumor location, magnetic resonance images, surgical margin, and pathologic diagnosis of the identified cohort were reviewed. The time to local recurrence or metastasis, follow-up duration, and the patients’ final status were analyzed. Results: The patients comprised seven male and four female patients with a mean age of 59 years (43–73 years). The tumor location was in the thigh in five, inguinal in two, upper arm in two, forearm in one, and popliteal in one. The average tumor diameter was 12 cm (3.5–27.0 cm). At the time of diagnosis, one patient was American Joint Committee on Cancer stage IB, two were II, four were IIIA, and four were IIIB. Local recurrence occurred in four, and distant metastasis occurred in five. The five-year overall survival of patients with DDLPS was 54.5±17.6%, and four died due to disease progression. Conclusion Primary DDLPS in the extremities is a subtype of liposarcoma with a poorer prognosis than well-differentiated liposarcoma and myxoid liposarcoma.