Ultrasound-Guided Distal Thoracolumbar Fascia Hydrodissection at the Gluteal Junction: A Technical Report With Cadaveric Assessment of Compartmental Spread and Gross Neural Sparing

Chronic low back pain with radiating lower-extremity symptoms in the absence of clear radiculopathy or major central canal stenosis remains a common diagnostic and therapeutic challenge. In patients with radiating low back pain without a convincing compressive correlate, posterior myofascial structures may be considered among several potential contributors; however, the present report evaluates the anatomical feasibility of a distal thoracolumbar fascia (TLF) hydrodissection approach rather than a clinical pain generator. We developed an ultrasound-guided hydrodissection technique targeting the distal TLF deep to the gluteus maximus and inferior to the sacroiliac joint. This technical report describes the clinical rationale, procedural technique, and cadaveric dye-spread assessment of injectate distribution and gross neural sparing. The technique was developed for a selected clinical context characterized by chronic low back pain radiating to the posterior thigh or calf, intact motor function, and lumbar magnetic resonance imaging (MRI) findings that may include fatty infiltration of the lower lumbar multifidus, with or without involvement of the gluteal origin region, after limited or unsustained benefit from standard image-guided interventions. For the described clinical technique, the symptomatic side would receive 10 mL of injectate prepared to a final concentration of 15% dextrose with 0.1% lignocaine. For cadaveric assessment, three fresh-frozen cadavers (two male, one female; mean age 74.3 years) underwent bilateral ultrasound-guided injection of the same target plane, yielding six injected sides. Each side received 10 mL of undiluted 1% methylene blue. Layered dissection demonstrated cephalad spread to approximately the L3 level in six out of six sides (100%). Multifidus staining occurred in six out of six (100%) and longissimus thoracis staining in six out of six (100%), whereas iliocostalis lumborum staining occurred in 0 out of six (0%). Partial proximal sacrotuberous ligament staining was observed in six out of six (100%). No gross dye was observed in the sciatic nerve, sacral plexus, neural foramina, or epidural space in 0 out of six sides (0%). In this fresh-frozen cadaver model, ultrasound-guided injection at the distal TLF-gluteal junction was technically achievable and produced a consistent gross cephalad dye-spread pattern toward the posterior fascial-paraspinal region. Because both sides of each cadaver were injected, the present design was not intended to determine contralateral crossover. These cadaveric findings do not exclude microscopic spread and do not establish histologic or in vivo safety. They also do not establish safety or efficacy of the described injectate formulation at this target in living patients. This report should be interpreted as hypothesis-generating rather than evidence of clinical effectiveness or safety.