These results establish preliminary procedural feasibility rather than clinical efficacy, and the researchers emphasized that validation in living animals is still required. The ventral branches of the L6 and L7 spinal nerves form much of the lumbosacral trunk, which continues as the sciatic nerve, with smaller contributions from S1 and a variable contribution from S2. These nerves give rise to branches that supply the pelvic-limb muscles and skin.

At the lumbosacral junction, narrowing of the vertebral canal or intervertebral foramina, together with ventrolateral vertebral new bone formation, can compress the L7 spinal nerve and impair its accompanying blood vessels. Nerve displacement, compression, vascular impairment, inflammation, perineural fibrosis and demyelination may therefore occur in the region. Degenerative lumbosacral stenosis is common in dogs and has been associated with compressive neuropathy in as many as 68% of cases.

Perineural injection therapy places medication around a targeted nerve under image guidance. Ultrasound- and fluoroscopy-guided approaches have previously been described for the canine lumbosacral junction, while ultrasound-guided dorsal and lateral approaches have been investigated around the L5 and L6 foraminal regions in canine cadavers. A ventral approach targeting L7 with ultrasound alone had not previously been described.

The investigators sought to identify the L7 nerve ventral to the L7–S1 neuroforamina and place injectate at the level of the nerve and foramen while avoiding nearby major vessels, the colon and the femoral nerve. Their success criteria focused on placement: computed tomography had to show direct contact between contrast material and the L7 nerve within a defined anatomical compartment. The prospective, single-center feasibility study involved seven cadavers of medium- to large-breed dogs, each weighing at least 15 kg.

The animals had died or been euthanized for reasons unrelated to the experiment, and owners had consented to scientific use of the bodies. Their median age was seven years, with a range of three to 11 years; median body weight was 39 kg, with a range of 23 to 61 kg; and median body condition score was 5 on the nine-point scale, with a range of 4 to 8. Two dogs were overweight, with body condition scores of 7/9 and 8/9.

Four cadavers had no visible osseous changes at L7–S1, whereas three showed moderate ventral or ventrolateral spondylosis deformans. Among those three, two also had foraminal narrowing, one had mild articular process hypertrophy and one had irregular vertebral endplates. One affected cadaver had an asymmetrical transitional lumbosacral vertebra.

Before injection, each lumbosacral junction was scanned by photon-counting computed tomography with the cadaver in dorsal recumbency and the hind limbs extended. Images were reconstructed with both soft-tissue and bone algorithms. For ultrasound imaging, an ECVDI diplomate and second-year imaging resident first visualized the junction in a mid-sagittal plane, then fanned the transducer laterally and angled it caudally to locate the L7 spinal nerve ventral to the L7–S1 neuroforamina.

The transducer was subsequently rotated into a transverse plane. Nearby landmarks, including the external iliac veins and arteries, L6 spinal nerve, colon and femoral nerve, were identified to plan a trajectory that avoided puncture of those structures. Gentle to moderate transducer pressure generally improved visualization of the spinal nerves and displaced intestines, the urinary bladder and large vessels.

An injection path through the iliopsoas muscle was accepted when needed to reach a safe route to the nerve. A 20- or 22-gauge needle, selected according to cadaver size and the depth of the target, was inserted medial to the transducer in an in-plane approach. The shaft and tip remained visible on real-time B-mode ultrasonography as the needle advanced mainly in a ventrodorsal direction.

For each side, the investigators deposited 0.6 milliliters of a one-to-one solution containing methylene blue and the non-ionic iodinated contrast agent Accupaque 300 at the level of the L7 nerve and neuroforamen. Ultrasound was used to observe dye spread during injection, after which a repeat CT scan was performed in the same position and with the same parameters as the pre-procedural scan. A cadaver selected with owner consent was also dissected anatomically to confirm staining of the L7 nerve and inspect regional tissue for dye distribution, vascular damage and epidural contamination.

On CT, an injection was considered successful when contrast material directly contacted the L7 spinal nerve within the compartment bounded dorsally by the iliocostalis lumborum muscle and pelvic surface of the sacrum and laterally by the iliopsoas muscle. Among the 11 successful injections, five showed circumferential distribution corresponding to an indirectly outlined tubular nerve segment, three encompassed approximately half of the nerve circumference and three made direct contact without encircling the nerve. Bilateral success occurred in five cadavers, while one additional cadaver had unilateral success.

Five of six injections succeeded among the three cadavers with degenerative lumbosacral changes, including the cadaver with a transitional vertebra. The three failures all occurred in the two overweight cadavers. No inadvertent contrast injection into blood vessels, the peritoneal space, colon or urinary bladder was detected.

Contrast extended into the neuroforamen in three specimens, with minimal epidural extension in two. Anatomical dissection of the selected 3.5-year-old Labrador Retriever confirmed bilateral, symmetrical and circumferential methylene-blue staining of the proximal L7 nerves, extending more than two centimeters on each side. The L6 branch joining L7 was stained in its entirety, and its small obturator branch showed mild staining on the right and marked staining on the left.

The proximal obturator nerve was strongly stained up to the point where that branch joined. Regional connective tissue and fat surrounding the dyed nerves were also stained, as was tissue ventral to the caudal half of the L7 vertebral body on one side. This dissection supported the CT interpretation of injectate placement, although direct anatomical confirmation was available for only one of the seven cadavers.

Several limitations constrain what can be inferred. The sample was small and drawn from one institution, so the results are descriptive and cannot establish safety, pain relief or functional benefit in living dogs. Cadaveric tissues also lack physiological conditions present in anesthetized patients, including body temperature, muscle tone, vessel pulsation and lymphatic or venous drainage; these factors could alter injectate spread.

The study mixture contained 50% contrast agent, increasing viscosity compared with liquid medications typically used for perineural injection therapy and likely affecting distribution. Lower-viscosity solutions may spread over a larger area. Procedures were performed by a board-certified diagnostic imaging diplomate and an imaging resident, but the effect of differences in training and operator experience was not evaluated.

Ultrasound visibility can also be impaired by intestinal gas. A redundant, gas-dilated descending colon complicated access to the right L7 nerve in one cadaver, while proposed preparatory measures such as an enema or bladder emptying were not evaluated. Overall, the results suggest that ultrasound can guide a ventral needle trajectory to the canine L7 spinal nerve, including in specimens with degenerative lumbosacral changes.

The approach may be particularly compatible with ultrasound guidance because manual transducer pressure can displace intervening structures while the operator watches the needle and its tip continuously. Body condition nevertheless emerged as an important variable: all five injections in normal-weight cadavers succeeded, compared with five of six injections in cadavers with degenerative changes, while all failures occurred in overweight animals. Technical success did not establish therapeutic success.

The extent of contrast coverage considered adequate on imaging has no established threshold for predicting clinical benefit, and the relationship between perineural distribution and pain relief remains uncertain. The study therefore provides a procedural foundation for further work but does not yet show that ultrasound-guided L7 perineural injection can safely relieve pain or improve function in living dogs. Subsequent in vivo studies must determine spread under physiological conditions, quantify adverse events, measure therapeutic benefit and establish how strongly outcomes depend on operator experience.

Subject of Research: Cadaveric feasibility of ultrasound-guided perineural injection of the canine L7 spinal nerve

Article Title: Ventral approach for ultrasound-guided perineural injection of the canine L7 spinal nerve: a cadaveric feasibility study

Article References: Dittmann, R., Haenssgen, K., Kaessmeyer, S., Schweizer, D., & Barge-Carmona, P. (2026). Ventral approach for ultrasound-guided perineural injection of the canine L7 spinal nerve: a cadaveric feasibility study. Frontiers in Veterinary Science, 13, Article 1932351. https://doi.org/10.3389/fvets.2026.1932351

Image Credits: AI Generated

DOI: 10.3389/fvets.2026.1932351

Keywords: canine L7 nerve, ultrasound guidance, perineural injection, veterinary imaging, lumbosacral neuropathy, dog cadavers, computed tomography, procedural feasibility, Ventral, approach, ultrasound-guided, perineural