Long-Term Hardware Failure and Autofusion Rates for Spinal Oncology

Objective: To assess long-term hardware durability and spontaneous autofusion in patients with spinal metastatic disease treated with posterior instrumentation without a fusion substrate. Summary of Background Data: Posterior stabilization for spinal metastatic disease is traditionally performed without fusion materials due to limited prognosis and impaired bone healing. As modern cancer treatments improve survival, the long-term effectiveness of non-fused constructs and the possibility of spontaneous autofusion remain uncertain. Methods: Consecutive spinal oncology patients treated with posterior instrumentation from 2010 to 2021 were screened. Inclusion required malignant disease, posterior-only fixation, and survival of at least five years. Long-term CT imaging (covering five or more years postoperatively) was reviewed for hardware failure—defined as screw loosening, back-out, rod fracture, or construct migration—and for spontaneous autofusion, which was defined as continuous bridging bone across anterior and/or posterior elements. Descriptive statistics and exact 95% CIs were calculated. Results: Out of 245 surgical patients, 15 long-term survivors met inclusion criteria, with a mean follow-up of 106.9 months. No radiographic hardware failures were observed (0%; 95% CI: 0.0–21.8%). Spontaneous autofusion occurred in 8 of the 15 patients (53.3%), with combined anterior-posterior bridging in 4 of 15 (26.7%). Autofusion was most common in thoracic constructs (71.4%). Using a 3% reference hardware failure probability, the chance of seeing zero failures in this group was 64%. Conclusions: No late hardware failures were observed at ≥5 years after posterior instrumentation without fusion substrate, whereas spontaneous autofusion occurred in over half of long-term survivors. These findings indicate that delayed biological stabilization may help ensure long-term construct durability and could lessen the need for formal arthrodesis in select spinal oncology patients.