Separation Surgery for Metastatic Spine Disease: How Often Are We Achieving True Separation?

Introduction: When performing separation surgery for metastatic spine disease, obtaining postoperative imaging is vital to plan for stereotactic radiation. In patients undergoing separation surgery for metastatic spine disease, we sought to: 1) determine the proportion of patients who received postoperative imaging, 2) evaluate the extent of separation in each case, and 3) compare oncologic outcomes in patients with adequate separation vs. not.

Methods: A single-center, retrospective cohort study was performed for all the patients who underwent separation surgery for metastatic disease between 2010-21. Inclusion criteria were: received postoperative radiation (RT) as external beam or stereotactic radiation (EBRT/SBRT). The primary outcome was tumor separation from the spinal cord, evaluated only in patients with postoperative MRI/CT-myelogram. Separation distance was evaluated by both an attending radiation oncologist and neurosurgeon. The a-priori separation distance goal between tumor and spinal cord was 3mm. Secondary outcomes were survival and local recurrence. Descriptive and bivariate statistics were performed.

Results: Of 239 patients undergoing separation surgery for metastatic spine disease, 113 patients (47.3%) received postoperative RT within three months (21.2% SBRT/78.8% EBRT). Postoperative imaging was performed in 29/113 (25.7%) patients, most commonly MRI (96.6%), with the following demographics: mean age 59.4±10.8 years, 55.2% male, most commonly lung (27.6%) primary. Ten patients had uninterpretable MRIs, leaving 19 evaluable images where the spinal cord could be visualized. Separation goal of 3mm was not achieved in 15/19 (78.9%) patients. Local recurrence was not significantly different between those with adequate separation vs. without (25.0% vs. 33.3%,p=1.000). There was no difference in death at 1-year in patients with adequate separation vs. without (50.0% vs 72.7%,p=0.560) or median time to death (332±252.5 vs. 237±130 days, p=0.695).

Conclusion : Only 26% of patients undergoing separation surgery received postoperative imaging for radiation planning, and among those with interpretable imaging, only 21% achieved the target separation of 3mm. Among the entire sample, 2% of patients had postoperative imaging that confirmed adequate separation. Vast room for improvement exists in confirming true separation between tumor and spinal cord in metastatic spine surgery.