Delayed Sacral Insufficiency Fracture Following Oncologic Resection of a Chondrosarcoma: Emphasizing the Role of Biomechanical Risk Assessment.

Introduction: Sacral chondrosarcoma is a primary malignant bone tumor for which en bloc resection remains the standard treatment. Given its location and role within the pelvic ring continuity, it poses a surgical and reconstructive challenge. Even with successful oncologic resection, the lack of a comprehensive preoperative biomechanical analysis may contribute to late-onset complications requiring reinterventions and impair the patient's quality of life. Case Report: The case describes a 41-year-old woman with no previous diagnosis of osteoporosis or prior fractures who underwent en bloc resection of a sacral chondrosarcoma at the S1-S2 level, without initial complications. Six months post-operatively, the patient returned with pain and gait impairment. An insufficiency fracture at the S1 vertebral body and residual sacral wing was identified, without signs of tumor recurrence or associated fluid collection. It was managed with posterior lumbopelvic fixation, with a favorable outcome and recovery in a 5-year follow-up. Conclusion: This case underlines the importance of the biomechanical integrity of the pelvic ring. It raises the need for assessment of the biomechanical risk within the oncologic surgical planning, despite the absence of classical bone fragility factors. Thus, structural destabilization of the pelvis must consider corrective or preventive strategies to prevent complications. A comprehensive analysis of these factors allows for improved functionality and patients quality of life.