Cumulative Incidence and Risk Factors for Secondary Alloplastic Cranioplasty: A Time-to-Event Analysis

Although complications of autologous bone flap cranioplasty are well described, data on long-term bone flap survival and the comorbidities associated with secondary reconstruction are limited. This study aimed to quantify the need for secondary alloplastic cranioplasty within a standardized patient cohort. Patients who underwent delayed cranioplasty following craniectomy with banked, frozen autologous bone between 2012 and 2025 were identified and analyzed using Cox regression, spline analysis, and Kaplan-Meier survival analysis. A total of 367 patients with an average age of 39.2±19.7 years (range: 0.3-84.4 years) at the time of cranioplasty were included. A secondary cranioplasty was required in 13.6% of patients (n=50 of 367), with resorption (52%) and infection (42%) as the most common indications. In adjusted analyses, patients who underwent cranioplasty following a traumatic injury (HR: 2.37; 95% CI: 1.07-5.26; P=0.03) and patients younger than 18 years (HR: 2.99; 95% CI: 1.35-6.62; P=0.01) were more likely to require a secondary cranioplasty due to bone flap resorption. Increasing defect size was also associated with a higher risk of secondary cranioplasty due to bone flap resorption, becoming significant at roughly 95 cm² (HR: 2.54; 95% CI: 1.04-6.20; P=0.04). The estimated cumulative incidence of secondary cranioplasty was 37% at ten years after autologous reconstruction. These results indicate that although autologous bone flap cranioplasty is largely effective, select patients face a substantially higher risk of secondary cranioplasty, and alternative reconstructive options may be warranted.