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Vulnerability of different nerves to intrafascicular injection by different needle types and at different approach angles: a mathematical model
  1. Margarita Sanromán-Junquera1,
  2. Andre Boezaart2,3,
  3. Yury Zasimovich4,
  4. Olga C Nin4,
  5. Xavier Sala-Blanch5,
  6. Jose De Andres6 and
  7. Miguel A Reina7
  1. 1Cardiac Arrhythmia Heart Failure (CAHF) Division, Abbott Medical España SA, Madrid, Spain
  2. 2The Alon P Winnie Research Institute, Gainesville, Florida, USA and Still Bay, Still Bay, South Africa
  3. 3Division of Acute and Perioperative Pain Medicine, Department of Anesthesiology and Department of Orthopaedic Surgery, University of Florida College of Medicine, Gainesville, Florida, USA
  4. 4Division of Acute and Perioperative Pain Medicine, Department of Anesthesiology, University of Florida College of Medicine, Gainesville, Florida, USA
  5. 5Human Anatomy and Embryology Unit, Faculty of Medicine, Universitat de Barcelona and Department of Anesthesiology Hospital Clinic, Barcelona, Spain
  6. 6Department of Anesthesiology, Critical Care and Pain Management General University Hospital, School of Medicine, University of Valencia, Valencia, Spain
  7. 7CEU San Pablo University School of Medicine and Department of Anesthesiology, Madrid-Montepríncipe University Hospital, Madrid, Spain
  1. Correspondence to Dr Andre Boezaart, Anesthesiology, Orthopaedic Surgery, University of Florida College of Medicine, Gainesville, FL 32610, USA; ABoezaart{at}


Background and objectives We assume that intrafascicular spread of a solution can only occur if a large enough portion of the distal needle orifice is placed inside the fascicle. Our aim is to present and evaluate a mathematical model that can calculate the theoretical vulnerability of fascicles, analyzing the degree of occupancy of the needle orifice in fascicular tissue by performing simulations of multiple positions that a needle orifice can take inside a cross-sectional nerve area.

Methods We superimposed microscopic images of two routinely used nerve block needles (22-gauge, 15° needle and 22-gauge, 30° needle) over the microscopic images of cross-sections of four nerve types photographed at the same magnification. Fascicular tissue that was overlapped between 80% and 100% by a needle orifice was considered at risk to possible intrafascicular injection. The effect of three angular approaches was evaluated.

Results There were statistical differences between the vulnerability of fascicular tissue depending on nerve type, the bevel angle of the needle and the angle approach. Fascicular vulnerability was greater in nerve roots of the brachial plexus after using a 22-gauge 30° needle, as was choosing a 45° angle approach to the longitudinal axis of the nerve.

Conclusions Our results suggest that clinicians may want to consider needle insertion angle and bevel type as they perform peripheral nerve blocks. Furthermore, researchers may want to consider this mathematical model when estimating vulnerabilities of various nerves, needle types and angles of approach of needles to nerves.

  • regional anesthesia
  • anatomy
  • basic science: other

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  • Contributors The following authors contributed to the design, conduct and reporting of the results: MS-J, AB, YZ, OCN, XS-B, JDA and MAR. Additionally, MS-J was responsible for the statistical analyses. Data collection was performed by MS-J and MAR.

  • Funding Support was provided solely from institutional and/or departmental sources (School of Medicine, University of CEU San Pablo, Madrid, Spain; Department of Anesthesiology, University of Florida College of Medicine, Gainesville, Florida, USA and Alon P. Winnie Research Institute, Still Bay, South Africa).

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Ethics approval The study was approved by the Grupo Hospital Madrid (Madrid, Spain) Clinical Research Ethics Committee (code 09.05.047-GHM).

  • Provenance and peer review Not commissioned; externally peer reviewed.