Outcomes and Complications After LUMiC® Endoprosthetic Reconstruction of Periacetabular Defects-A Retrospective Cohort Analysis.

(1) Background: The reconstruction of periacetabular defects after tumor resection remains one of the most challenging procedures in orthopaedic oncology. The modular LUMiC® system was designed to improve fixation stability and reduce implant-related complications compared with earlier hemipelvic prostheses. We investigated patient and implant survival after LUMiC® reconstruction, complication types and functional outcomes. (2) Methods: Eighteen patients (8 men, 10 women; mean age 58.9 years) underwent LUMiC® endoprosthetic reconstruction between 2011 and 2025. Kaplan-Meier analysis was used to estimate patient and implant survival. Complications were categorized according to Henderson. Functional results were evaluated at follow-up using MSTS and TESS. (3) Results: Mean follow-up was 35.52 months (SD 36.89). Overall implant survival was 72.2%. Instability (27.8%) and infection (16.7%) were the leading complications. Two-thirds of patients required at least one revision (mean 3.1 revisions per case). Metastatic disease reduced patient survival (p = 0.012) but did not affect implant longevity (p = 0.31). Functional outcomes were available for only 3 of 18 patients and should therefore be regarded as exploratory. Mean MSTS was 58.9% (SD 21.43) and mean TESS was 73.4% (SD 6.836). (4) Conclusions: Despite high revision rates, the LUMiC® prosthesis provides durable fixation. Early revision does not appear to compromise implant survival. However, the small and heterogeneous cohort represents a limiting factor of this study.