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Histological Confirmation Of Needle Tip Position During Ultrasound-Guided Interscalene Block: A Randomized Comparison Of Intraplexus And Periplexus Approach

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Histological Confirmation Of Needle Tip Position During Ultrasound-Guided Interscalene Block: A Randomized Comparison of Intraplexus And Periplexus Approach

Jennifer Szerb, MD FRCPC, Justin Greenberg, MD FRCPC, M. Kwesi Kwofie, M.D., FRCPC, William Baldridge, PhD, Robert Sandeski, Juan Zhou, MD Ph.D
Department of Anesthesia, Pain Management and Perioperative Medicine, Dalhousie University, Halifax, Nova Scotia, Canada


Recent Regional Anesthesia research has examined how best to avoid direct contact with nerves, while still achieving a reliable neural blockade.(1) Ultrasound-guided interscalene block can be performed using either a peri-plexus needle placement or intra-plexus needle placement with similar efficacy. (2) No studies have examined the needle tip position in relation to the neural tissues with microscopic precision associated with the two techniques. Our objective was to investigate the risk of sub-epineurial needle tip placement in cadavers resulting from the two ultrasound-guided techniques. 

Materials and Methods:

After IRB approval, 52 injections were performed on 26 lightly embalmed cadavers, with side, order, and technique assigned randomly. Under real-time ultrasound guidance the block needle was placed next to the hyperechoic layer of the plexus (periplexus, Figure 2A) or between the hypoechoic nerve roots (intraplexus, Figure 2B). Once positioned, 0.1 mL of black acrylic ink was injected. Effort was taken to avoid direct contact with the hypoechoic structures at all times. Ultrasound video clips were taken of the needle approach and the injection. Tissues were removed, histology sections prepared, and coded by two reviewers blinded to group allocation (periplexus or intraplexus). Where disagreement occurred, an anatomist with pathology expertise determined the ink deposition in relation to neural tissues. Videos clips were reviewed by two experienced regional anesthesiologist that were not otherwise involved in the study as well as the investigator who performed  the procedures and coded the videos as either an intraplexus or periplexus approach. Ultrasound still images were used to calculate the distance from the needle tip to the closest observed nerve root. Sample size was estimated based upon the previously reported 50% sub-epineurial injection rate with the intraplexus technique,(3) considering a reduction to 10% with the periplexus technique to be clinically relevant. 


No sub-epineurial ink deposits were observed in the periplexus group. Sub-epineurial ink deposition was observed in 3/26 (11.5%) of intraplexus injections. Furthermore, two (of the three) sub-epineurial ink deposits were observed under the perineurium in the intraplexus group. In fact, in the samples with sub-perineurial ink, ink was found to involve all fascicles of the root with little spread through the extra-perineurial space. No statistical difference in the sub-epineurial rate was found between the periplexus versus intraplexus injections (two-sided Fisher’s Exact Test p = 0.23). There was substantial agreement between the video assessors and the investigators intended experimental needling technique (Cohen’s Kappa Statistic = 0.92). The average distance for the periplexus technique from needle tip to the lateral border of the brachial plexus was 0.36mm (range 0.1-0.7, SD 0.16). 


Our results show that during intraplexus approach, there is an 11.5% chance that the needle tip position may be sub-epineurial. The subperineural injections involving all fascicles may demonstrate the interconnectedness of the largely non-compliant sub-perineurial network if only 0.1 mL of volume may lead to distant spread with out extra-perineurial spread (Figure 4A & 4B). The periplexus technique resulted in no sub-epineurial spread of ink, suggesting that this approach may be less likely to result in mechanical trauma to nerves from direct needle injury. 


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