Introduction: Ultrasonography is useful for detecting intraneural injections. However, the reliability of the sonographic findings of intraneural and subparaneural injections in terms of true spread location and their association with intrafascicular deposits has not been systematically evaluated.
Evidence acquisition: Our objectives were: 1) to explore the reliability of sonographic findings of intraneural and subparaneural injections when validated with tests of true spread such as histology, dissection, or imaging; and 2) to evaluate their association with intrafascicular deposits. A scoping review was conducted according to Joanna Briggs guidelines. Cinahl, PubMed, ProQuest, ScienceDirect, Scopus and Cochrane databases were searched for studies on adults, cadavers, and animal models. Pediatric studies were excluded.
Evidence synthesis: The search strategy found 598 citations. Following screening, 19 studies were selected. Intraneural injections occurred in the brachial plexus, sciatic, femoral, and median nerves. Subparaneural injections in popliteal, supraclavicular and interscalene blocks. Sixteen different ultrasound findings were used to label injection location. Subepineural deposits within individual nerves occurred occasionally following subparaneural injections, regardless of nerve expansion. Overall, five studies reported intrafascicular deposits, two of which frequently, following intraneural and subparaneural injections. None of the currently used ultrasound findings was predictive of intrafascicular deposits.
Conclusions: Our results suggest that sonographic parameters of intraneural and subparaneural injections are reliable in terms of detecting spread location. Intrafascicular injectate deposition may occur, albeit infrequently, particularly in the proximal brachial plexus. Our findings support the judicious interrogation of sonographic parameters suggestive of incipient intraneural injection.