Effect of approach, volume and morphometry on dye spread to the quadratus lumborum plane in canine cadavers.

Objective: To compare dye spread after injection in the quadratus lumborum plane (QLP) via transmuscular and lateral approaches with different volumes in canine cadavers.

Study design: Cadaveric, experimental, prospective study.

Animals: A group of 58 canine cadavers.

Methods: Cadavers were classified by body mass as small (S, < 10 kg), medium (M, 10-20 kg) or large (L, > 20 kg). Morphometric data (mass, body condition score, axial length, abdominal and thoracic circumference) were recorded. Ultrasound-guided QLP injections with 0.15, 0.3 and 0.6 mL kg^-1 of 0.1% methylene blue were performed via transmuscular or lateral approaches on both hemiabdomens. Craniocaudal and dorsoventral dye spread, the number of stained ventral branches of thoracolumbar spinal nerves (VBSNs) and whether the sympathetic trunk was stained were evaluated. Technique and dissection times, along with visibility scores for reference structures, needle and the injected solution within the QLP were recorded. Statistical analysis included two-way analysis of variance, Kruskal-Wallis, Pearson correlation and multiple regression tests, with significance set at p < 0.050.

Results: Morphometric variables influenced only the craniocaudal spread (p < 0.001). Craniocaudal spread did not differ significantly between approaches (p = 0.766) but was significantly influenced by volume (p < 0.002). However, greater craniocaudal spread did not result in an increased number of stained VBSNs (p = 0.488). The number of VBSNs stained was lower with 0.15 mL kg^-1 (p < 0.013), with no differences observed between 0.3 and 0.6 mL kg^-1 (p = 0.488). The most frequently stained VBSNs were L2, L3 and L1, in that order.

Conclusions and clinical relevance: There were no significant differences in dye spread between transmuscular and lateral approaches. Injectate volume affects spread, but volumes > 0.3 mL kg^-1 do not increase the number of stained VBSNs. Morphometric variables do not affect the number of stained VBSNs.