Spinal cord protection by epidural separation during vertebral cryoablation for metastatic spine disease: A...

Cryoablation for spinal metastases is limited by the risk of cryogenic neural injury near the spinal cord. Physical separation between the vertebral body and dura may provide a thermal margin, but the distance-temperature relationship in the epidural space remains insufficiently defined.

This exploratory study aimed to map the association between surgically created epidural separation distance and local thermal and neurophysiological changes during vertebral cryoablation in a canine model.

In a non-randomized, unblinded, two-phase pilot study, we first performed in vitro phantom experiments (0-, 2-, and 5-mm air gaps). Subsequently, 12 beagle dogs were assigned to three groups (n = 4 each): 0-mm (control), 2-mm, or 5-mm epidural separation, followed by T13 vertebral cryoablation. Primary outcomes were the minimum epidural temperature at the ventral midline and 30-min compound muscle action potential (CMAP) amplitude recovery.

In vitro, greater separation distance was associated with significantly warmer target-point temperatures (P < .001). In vivo, a 5-mm separation produced warmer ventral midline epidural temperatures, which remained above a previously reported safety estimate of 4 °C, and greater CMAP recovery compared to a 2-mm separation (P = .024 and P = .028, respectively).

In this proof-of-concept canine study, epidural separation distance was associated with ventral epidural temperature and short-term CMAP recovery during vertebral cryoablation. These findings do not establish a clinical safety threshold and require validation in clinically relevant models, including studies with survival and histologic assessment.