An ultrasound-guided subparaneural approach to the sciatic nerve in the dog: a cadaver study

Abstract Objective To describe the gross and microscopic anatomy of the sciatic nerve paraneural sheath and to report an ultrasound-guided subparaneural approach to the sciatic nerve in dogs, comparing two different volumes of injectate. Study design Prospective, randomized, anatomical study. Animals A group of nine middle-size adult mongrel canine cadavers (18 limbs). Methods The sciatic nerves of three pelvic limbs of two canine cadavers were identified, exposed, and isolated between the greater trochanter and the popliteal fossa for gross anatomical and microscopic examination. An additional three pelvic limbs were surgically dissected on the lateral surface of the limb; the sciatic nerves were isolated, and a 26 gauge over-the-needle catheter was inserted through the paraneural sheath under direct visualization. A methylene blue solution was then slowly injected into the subparaneural compartment through the catheter under ultrasound (US) visualization using an 8-13 MHz linear-array transducer. Subsequently, 12 pelvic limbs (six cadavers) were randomly allocated to one of two groups, using an US-guided percutaneous subparaneural approach either 0.1 mL kg-1 or 0.05 mL kg-1of a 1:1 solution of methylene blue and 0.5% bupivacaine was injected. The spread of the dye solution and the amount of nerve staining were macroscopically scored. The stained sciatic nerve with their sheaths were then harvested for microscopic examination. Results The paraneural sciatic nerve sheath was easily identified distinct from the nerve trunk both macroscopically and with US visualization, and microscopically. Complete staining was achieved in five/six (83.3 %) sciatic nerves in each group; no difference was found in the amount of staining between the two groups. Microscopically, no signs of sciatic nerve intraneural injection were observed. Conclusions and clinical relevance The US-guided subparaneural injection of 0.05 mL kg-1 of a dye injectate resulted in satisfactory nerve staining without evidence of sciatic nerve intraneural injection.