Thoracolumbar Retrolaminar Block: Anatomical and Radiological Study of Injectate Pattern Distribution in Canine Cadavers

SIMPLE SUMMARY: The analgesic management of dogs with spinal disease is important, as insufficient pain relief may result in chronic neuropathic pain. The retrolaminar block is a relatively new local anaesthetic technique, first developed in humans, in which the local anaesthetic is deposited into the musculofascial plane on the lamina of the target thoracic vertebra, thus providing analgesia to the thoracic region. The aim of this study was to evaluate the retrolaminar technique as a peri-operative analgesic option for dogs with spinal disease, by determining the distribution of two volumes of contrast-dye mixture and the potential complications after anatomical landmark-guided thoracolumbar retrolaminar injections in canine cadavers. Eight canine (greyhound) cadavers were randomised into two groups that received either a 10 or a 20 mL injection into the retrolaminar space at the level of the twelfth thoracic vertebra, after which they underwent computed tomography and anatomical dissection to determine the spread of the injectate. The injectate was detected in the surrounding intervertebral foramina and the paravertebral and retrolaminar fascial planes, which could suggest promising analgesic potential for spinal pain. Epidural and retroperitoneal spread was also noted, and the spread was not volume-dependent. Further studies will help to determine the exact indications for this technique. ABSTRACT: The retrolaminar block is a regional anaesthetic technique, first developed in humans, in which the local anaesthetic is deposited directly onto the dorsal aspect of the thoracic or lumbar vertebral lamina. This study aims to evaluate the distribution of landmark-guided thoracolumbar retrolaminar injections in greyhound cadavers. Thirteen injections of contrast-dye solution were performed in eight cadavers at the level of the twelfth thoracic vertebra (T12), with either 20 mL (n = 8, high volume, HV) or 10 mL (n = 5, low volume, LV) per site. The spread of the injectate was evaluated through computed tomography and transverse anatomical dissection. The groups were compared using the Mann–Whitney U test. The median (range) of the extent of the spread was 4 (2–5) and 3 (2–4) intervertebral foramina in the LV and HV groups, respectively. The median (range) of the spread along the retrolaminar space was 3 (2–3) retrolaminar segments in the LV and 3 (2–4) in the HV group. Epidural and retroperitoneal spread was identified in seven cadavers. Following landmark-guided retrolaminar injections, the injectate spread both in the retrolaminar and paravertebral spaces, without any obvious association between the volume of injectate and the extent of the spread. Further studies are warranted to determine the clinical efficacy of the technique.