Histological confirmation of needle tip position during ultrasound-guided interscalene block: a randomized comparison between the intraplexus and the periplexus approach

India ink: a time-tested histological marker

“…In order to be an ideal marker of needle tip position, the dye must be retained within the connective tissue in which it is injected, and not permeate either the surface of epineurium or perineurium. We confirmed this feature of India ink in our prior study 4. Our research, and work by Orebaugh and colleagues, involved removing the dissected nerves, bathing them in India ink dye for 60 min followed by washing with saline, before histological preparation and examination.…”

“…While we applaud and share their interest in better understanding the impact of neural microanatomy on clinical care, they produce no evidence for their remarks regarding India ink, referencing only one study using lidocaine radiolabeled with carbon-14 to determine its intraneural concentration. In their recent paper,2 the work by Orebaugh and colleagues is the only reference cited,3 omitting a broad review of the use of India ink in pathology, as well as its use as a marker of needle tip position in studies of ultrasound guided peripheral nerve blocks 4…”

Ultrasound-guided block and the incidence of intraneural injection. A reply

“…Szerb et al recommend needle placement between the nerve roots [5]. In our simulation, the tangential approach used made no attempt to avoid direct needle to nerve contact, whereas accidental advancement in Szerb's study occurred in three intra-neural needle placements via the anterior scalene muscle during intramuscular injections.…”

Ultrasound-guided block and the incidence of intraneural injection

“…Histologically, this may make them more vulnerable to damage. The high density of axons may lead to difficulty in distinguishing between the boundaries of the various roots [2][3][4]. Moreover, the distance between the roots decreases as the ultrasound probe is moved distally and the boundaries of the neural structures blur.…”

“…In fact, in 2015, our group published two ultrasound-guided brachial plexus injection techniques at the interscalene groove [2], performing 52 peri-plexus and intraplexus interscalene injections in 26 cadavers, all with sonographic and histological confirmation of needle tip and injectate. Our intention was to have our needle tip in either the periplexus position [3], or between the nerve roots, without violating the epineurium around each of the nerve roots.…”