Background: Elevated intraspinal pressure (ISP) driven by cord swelling is hypothesized to cause secondary injuries following trauma. We previously observed comparable ISP elevations in pigs undergoing traumatic spinal cord injury (TSCI) and sham operations (standalone laminectomy), suggesting the presence of other drivers. Methods: Using a porcine model, we assessed whether ISP elevation was compartment specific, related to cerebrospinal fluid (CSF) restoration, or driven by epidural pressure. In three corresponding sub-studies, the ISP was measured in the spinal cord, subdural, and epidural compartments after TSCI (n=5), and the effects of CSF drainage (n=3) and leaving the surgical wound open were tested (n=6). Results: The spinal cord and subdural ISP increased comparably, validating subdural ISP as a proxy for spinal cord pressure. CSF drainage attempts yielded no fluid and did not affect the subdural ISP. Correspondingly, magnetic resonance imaging revealed that the CSF was displaced by a higher degree of epidural compression than by spinal cord swelling. Leaving the wound open reduced ISP 2.5-fold more than the TSCI itself, further implicating epidural pressure from post-laminectomy swelling as a major driver of elevated ISP. Conclusion Epidural pressure influences elevated ISP following TSCI and laminectomy, rather than spinal cord swelling alone or CSF reconstitution. These findings suggest caution against external compression after laminectomy and call for further investigation of elevated ISP in patients with TSCI.