Novel Ultrasound-Guided Popliteal Fascial Retinaculum Injection for Symptomatic Knee Osteoarthritis: A Technical Report With Cadaveric Dye-Distribution Study and Step-by-Step Procedural Description.

Knee osteoarthritis (OA) is increasingly understood as a whole-joint disorder involving not only articular cartilage but also synovium, capsule, ligaments, tendon insertions, and adjacent periarticular soft tissues. Fascial and interfascial tissues have attracted growing interest in musculoskeletal medicine because of their continuity, force-transmission properties, sensory innervation, and potential relevance to pain generation and movement dysfunction. We describe a novel ultrasound-guided posteromedial knee injection targeting the posteromedial fascial-periarticular convergence zone, referred to operationally in this report as the "popliteal fascial retinaculum." This term is used as a descriptive procedural framework rather than a formally established anatomical structure. This convergence region involves the semimembranosus insertion, popliteus, oblique popliteal ligament (OPL), posterior capsule, proximal superficial medial collateral ligament (MCL), and adjacent popliteal fascial layers. The technique uses a structured scanning sequence beginning with transverse safety mapping of the popliteal neurovascular bundle, followed by posteromedial landmark identification and longitudinal localization of the target convergence zone. A 5-inch 22-gauge spinal needle is advanced in plane under real-time ultrasound guidance, and 30 mL of 5% dextrose with 0.1% lignocaine is distributed across five predefined target planes. Cadaveric feasibility was assessed in four lower limbs using 30 mL of 0.1% methylene blue delivered under ultrasound guidance according to the described technique. Gross layered dissection demonstrated dye staining of the intended target structures together with substantial extension into adjacent fascial, periarticular, perineural, and perivascular planes, with proximal interfascial spread along the posterior thigh. Histologic confirmation of intraneural or intravascular spread was not performed. These findings support preliminary anatomical feasibility of regional access and spread, but do not establish selective targeting, procedural safety, histologic precision, or clinical efficacy. This technical report describes a reproducible ultrasound-guided posteromedial knee injection technique supported by cadaveric dye-distribution findings, detailed sonoanatomic landmarks, and procedural video documentation. The technique appears anatomically plausible and technically feasible as a regional interfascial-periarticular access approach, but further prospective work is needed to determine reliability, safety, mechanism, targeting specificity, and clinical effectiveness.