Ultrasound-Guided Humerus-Parallel Injectate Distribution to the Posterior Antebrachial Cutaneous Nerve-Related Fascial Plane and Common Extensor Origin: A Proof-of-Concept Cadaveric Anatomical Feasibility Study

Background: Lateral epicondylopathy is commonly approached as a tendinopathic disorder of the common extensor origin; however, persistent lateral elbow pain may also involve a superficial sensory nerve component related to the posterior antebrachial cutaneous nerve (PABCN). This proof-of-concept cadaveric anatomical feasibility study evaluated whether a single-window, humerus-parallel ultrasound-guided injectate pathway could simultaneously reach the superficial PABCN-related fascial plane and the common extensor origin. Methods: One fresh-frozen male cadaveric donor was used, and both elbows were injected under real-time ultrasound guidance. With the elbow flexed and the forearm pronated, the transducer was aligned parallel to the long axis of the humerus over the lateral epicondylar region. A 23-gauge, 6 cm needle was advanced in plane from distal to proximal over the common extensor aponeurosis, and 10 mL of 1% methylene blue was injected into each elbow. Layer-by-layer anatomical dissection was then performed by an anatomist who was not involved in the injection procedure. Gross linear dye spread was measured directly during dissection using the distal needle entry point as the reference point, and ruler-containing photographs were additionally reviewed using ImageJ software for supportive image-assisted assessment. Results: In both elbows, methylene blue stained the superficial PABCN-related fascial plane, including the anterior and posterior branches of the PABCN, and concomitantly covered the common extensor aponeurosis and lateral epicondylar enthesis. Dye spread measured approximately 10 cm proximally, 5 cm distally, and 4 cm anteriorly. No gross intra-articular dye deposition or focal intramuscular pooling was observed. Conclusions: This proof-of-concept cadaveric study demonstrates the anatomical plausibility of a single-window, enthesis-centered ultrasound-guided injectate pathway that includes both the superficial PABCN-related plane and the common extensor origin. These findings should be interpreted as descriptive anatomical feasibility observations and do not establish reproducibility across anatomical variants, clinical efficacy, safety, or procedural superiority.