A Tactile Trans-Flexor Carpi Radialis Surface Landmark Technique for Median Nerve Local Injection: A Cadaveric Study

Median nerve (MN) block under local anesthesia at the wrist is commonly performed but can be limited by anatomic variation, particularly absence of the palmaris longus tendon. This study investigates a novel trans-flexor carpi radialis (trans-FCR) technique for MN anesthesia that uses the flexor carpi radialis (FCR) tendon as a consistent surface landmark.

Fourteen fresh frozen upper extremity cadaver specimens were used. A 25-gauge needle was inserted through the FCR sheath approximately 4 cm proximal to the wrist crease in a transverse fashion, angled approximately 0° to the vertical and parallel to the wrist crease. The trans-FCR technique was tested against two other standard surface landmark techniques.

The trans-FCR technique avoided penetration of critical structures such as the MN (3.5 mm), radial artery (8.5 mm), and palmar cutaneous branch of the MN (3.8 mm). The MN crossed under the long finger flexor digitorum superficialis at an average of 4.0 cm proximally from the wrist crease with a range of 2.8-4.8 cm. Three specimens had absent palmaris longus. There was no difference in injury rate to surrounding critical structures regardless of palmaris longus presence. No incidences of MN penetration occurred with the trans-FCR approach.

The trans-FCR technique is an anatomically based method for MN block under local anesthesia that uses a consistent tactile landmark and without dependence on the palmaris longus tendon. Clinical studies are needed to evaluate its efficacy in vivo.

Basic Science Anatomic Research V.