Restoration of Spinopelvic Continuity with the Free Fibula Flap after Limb-Sparing Oncologic Resection Is Associated with a High Union Rate and Superior Functional Outcomes

Background: Type 1 internal hemipelvectomies and total sacrectomies cause significant biomechanical instability, demanding pelvic ring reconstruction for ambulation and torso support. Previously described methods include autografts, allografts, and implants, commonly with poor long-term outcomes. The authors hypothesized that the free fibula flap for spinopelvic reconstruction is safe and effective, and associated with a high bony union rate and superior functional outcomes. Methods: The authors performed a retrospective review of all patients who underwent free fibula flap surgery after internal hemipelvectomy or total sacrectomy at M. D. Anderson Cancer Center from 2003 to 2018. The primary outcome was radiographic evidence of bony union. Secondary outcomes included surgical-site occurrence and lower extremity function. Univariate and multivariate logistic regression analyses were performed. Results: Forty-seven patients were included (internal hemipelvectomy, n = 38; total sacrectomy, n = 9). The mean follow-up was 3.3 years and the most common abnormality was chondrosarcoma (30.4 percent). The nonunion rate was 9.7 percent and the surgical-site occurrence rate was 34 percent; there were no flap losses. Greater age was significantly associated with nonunion (OR, 1.1; 95 percent CI, 1 to 1.2; p = 0.003), whereas obesity was the only independent predictor of surgical-site occurrence (OR, 9.2; 95 percent CI, 1.2 to 71.3; p = 0.03). Functional metrics approached those of adult norms by 3 years postoperatively. Compared to internal hemipelvectomy patients, patients undergoing total sacrectomy had more comorbidities, a higher complication rate, and a worse functional outcome. Conclusion: The free fibula flap for spinopelvic reconstruction is safe and effective, and is associated with a high bony union rate and superior functional outcomes.