European Radiology

, Volume 30, Issue 2, pp 887–894 | Cite as

Carpal tunnel ultrasound: is the “safe zone” on the ulnar side of the median nerve really avascular?

  • Anne-Charlotte Sergeant
  • Sammy Badr
  • Marc Saab
  • Xavier Demondion
  • Anne Cotten
  • Thibaut JacquesEmail author



Numerous publications have studied the regional anatomy of the carpal tunnel to define a “safe zone” to reduce the risk of perioperative neurovascular complications. This zone, located between the ulnar neurovascular bundle and the median nerve, is considered to be safe mainly because of the absence of vascular structures. This study aims to assess the presence of arterioles within this area using superb microvascular imaging (SMI).

Materials and methods

The images from patients who underwent a bilateral routine wrist ultrasound with SMI, between January 28 and February 28, 2019, were retrospectively reviewed by two radiologists to evaluate the presence and location of arterioles in the safe zone. In addition, cadaveric wrists injected with intra-arterial red latex underwent dissection of the carpal tunnel.


The images from 27 patients (54 wrists) were reviewed. In the safe zone, arterioles were seen superficial to the retinaculum in 36 wrists (36/54; 66.7%) and deep to the retinaculum in 21 wrists (21/54; 38.9%). The arterioles located deep to the retinaculum were more frequently found close to the median nerve (21/54; 38.9%) than to the ulnar artery (9/54; 16.7%). In five cadaveric wrists, arterioles were detected superficial to the retinaculum in 3 wrists (3/5; 60%) and deep to the retinaculum in 2 wrists (2/5; 40%).


Arterioles can be seen in the safe zone both superficial and deep to the flexor retinaculum. Deep to the retinaculum, they are mainly observed in the proximal aspect of the carpal tunnel and more frequently close to the median nerve.

Key Points

• Superb microvascular imaging (SMI) enables the visualization of arterioles within the “safe zone” of the carpal tunnel (visible both superficial and deep to the flexor retinaculum).

• Arterioles were more frequently observed in the proximal aspect of the carpal tunnel.

• Deep to the retinaculum, arterioles were more frequently seen in proximity to the median nerve.


Ultrasound imaging Carpal tunnel syndrome Anatomy Arterioles 



Picture archiving and communication system


Pulsed Doppler


Superb microvascular imaging



The authors would like to thank Julien ADAM, Cassandre DUVINAGE, Benjamin LEJEUNE, and Quentin SION (medical students) who contributed to the cadaveric study.


The authors state that this work has not received any funding.

Compliance with ethical standards


The scientific guarantor of this publication is Thibaut Jacques.

Conflict of interest

The authors of this manuscript declare no relationships with any companies whose products or services may be related to the subject matter of the article.

Statistics and biometry

No complex statistical methods were necessary for this paper.

Informed consent

Written informed consent was waived by the Institutional Review Board.

Ethical approval

Institutional Review Board approval was obtained.


• Retrospective

• Observational

• Performed at one institution


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Copyright information

© European Society of Radiology 2019

Authors and Affiliations

  1. 1.Department of Musculoskeletal RadiologyLille University HospitalLilleFrance
  2. 2.Department of RadiologyUniversity Hospital of PoitiersPoitiersFrance
  3. 3.Department of Orthopaedic surgeryLille University HospitalLilleFrance
  4. 4.Lille University School of MedicineLilleFrance
  5. 5.Laboratory of AnatomyLille University School of MedicineLilleFrance

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