Evaluation of fusion status in patients with minimum 1-year survival post-oncologic spinal fusion.

Background Context: Oncologic patients have significant medical comorbidities which may impact arthrodesis after spine surgery. Furthermore, there is a paucity of published data describing fusion rates, and arthrodesis quality.

Purpose: In this study, we present institutional data for patients with minimum 1-year survival who underwent spinal fusion secondary to treatment of metastatic spine disease.

Study Design/setting: Retrospective cohort study done at a single tertiary medical center.

Patient Sample: Patients were selected from a single institution between 2012 and 2022. Included patients had spinal fusion as part of oncologic treatment, minimum of 1 year follow up, and postoperative Computed Tomography (CT) scan at minimum 1 year.

Outcome Measures: Patient outcomes included fusion status and Hounsfield units (HU) on CT scan at 1 year.

Methods: Retrospective chart review was performed collecting demographic and treatment information including postoperative oncologic and radiation treatment as well as HU along the cranial and caudal pedicles bilaterally on the 1-year CT scan. Indications for surgery included symptomatic metastatic disease. All surgeries were performed by 1 of 3 surgeons at a single tertiary medical center. Statistical analysis was performed using the Student T-Test and Chi-Squared Test.

Results: There were 74 patients presenting with metastatic spine disease who met inclusion criteria. Demographics included an average age of 61.9 years at time of surgery, median construct length of 6 levels, and median survival was 43.2 months. Our cohort demonstrated complete and partial fusion rates of 11.1% and 59.5%, respectively. There was a significant difference in average HU for patients demonstrating fusion at 1 year, 444.2 compared to those demonstrating a lack of fusion, 285.8 (p<.0001). Patients who received postoperative radiation had higher postoperative HU than those who did not receive radiotherapy (411.1 vs. 304.9, p=.042). There was no significant difference in fusion status based on postoperative chemotherapy status, p=.127. Additionally, there was no difference in HU based on SBRT versus conventional radiotherapy, p=.588.

Conclusion: Partial fusion was seen in over half of the study cohort at 1-year follow-up; complete fusion was seen in 11% of patients. Fused patients and those who received postoperative chemotherapy had significantly higher HU on 1-year CT. Maximizing control of cancer burden as well as improving bone quality may help patients with metastatic spine disease demonstrate bony fusion. More research is indicated to evaluate causal implications of survival in patients with metastatic spine disease that have undergone spinal fusion.