Background and Objectives Real-time ice-ball formation during cryoneurolysis has sparsely been assessed with ultrasound (US). Cryoneurolysis in lower back pain syndrome represents a validated management option in cases of facet joint syndrome. Ultrasound may be a useful tool to perform facet joint cryodenervation. The objective of this study was to assess, ex vivo, the ability of US to assess the ice-ball formation of a cryoneurolysis device.

Methods Ultrasound assessment of the ice-ball depiction was done using chicken muscle at 22°C in which several freezing cycles were performed with both 2.1- and 1.3-mm cryoprobes. For each freezing cycle, static images and dynamic videos were generated for both needle insertion and ice-ball formation with 18-, 11-, and 6-MHz transducers. The following data were assessed in each combination of cryoprobe and transducers: quality of needle tip visualization, quality of the ice-ball formation depiction, size of the ice ball, presence of a shadow cone, and usefulness of power Doppler mode to assess ice-ball formation.

Results The 18- and 11-MHz linear transducers allowed to directly depict the formation of the ice ball. Visualization of the cone shadowing allowed indirect visualization of the ice ball with both 18- and 11-MHz transducers. However, the ice ball was not depicted (directly or indirectly) with the convex 6-MHz transducer, and power Doppler was the only way to indirectly monitor the ice ball during the freezing cycles.

Conclusions Ultrasound is a useful tool to monitor the formation of ice ball during a cryoneurolysis freezing cycle. Power Doppler appears as the only option to monitor the ice ball with low-frequency transducers. This novel finding may be useful in cases of lumbar medial branch cryoneurolysis, an application we plan to assess in a future pilot prospective study.