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Relationships of Palmaris Longus and Long Finger Flexor Digitorum Superficialis Tendons to the Median Nerve and Ulnar Artery in the Proximal Carpal Tunnel
Ebrahim Paryavi, MD; University of Maryland School of Medicine; James Wilkerson, MD; Univeristy of Maryland; David Zelouf, MD; Thomas Jefferson University Hospital; Joshua Abzug, MD; University of Maryland Medical Center
University of Maryland School of Medicine, Baltimore, MD, USA


Endoscopic and minimally invasive two-incision carpal tunnel surgeries exploit the space between the ulnar artery (UA) and the median nerve (MN) to release the transverse carpal ligament. A precise understanding of the anatomy is needed to safely perform these procedures, yet the exact spatial relationships of the Palmaris Longus (PL) and Long Finger Flexor Digitorum Superficialis (FDSL) tendons to these critical structures at the level of the distal flexion crease of the wrist has not been described.


Thirteen matched pairs of fresh frozen cadaver upper limbs were utilized. Each specimen was dissected sharply with minimal disruption of the soft tissues to initially expose the PL, UA, and MN at the level of the distal wrist flexion crease. Measurements were taken using digital calipers from the UA and MN to the medial and lateral edges of PL and the FDSL. Each measurement was performed 3 times and then averaged. The PL was subsequently reflected proximally to expose the FDSL and analogous measurements were performed.


Five female and eight male matched pairs of cadaver upper extremities were used with all but 1 pair having a PL. The average distance from the medial border of PL to UA was 11.71 mm (std dev 2.74 mm, range 6.20-16.52 mm). The MN was found 1.22 mm (std dev 1.97) lateral to the medial border of PL. The lateral border of PL overlapped with the MN in all specimens. FDSL was 7.43 mm (std dev 2.65, range 2.76-12.10mm) lateral to the UA. The MN was 2.85mm (std dev 2.24) lateral to the medial edge of FDSL and 0.24 mm(std dev 0.46) lateral to the lateral edge of FDSL.

Summary Points

The median nerve lies extremely close to the medial edge of palmaris longus. Incisions performed that extend to the lateral border of PL may cause injury to the MN. The ulnar artery lies approximately 11mm medial to the medial edge of PL. An interval within 6mm of the medial edge of PL gives a buffer of 2 standard deviations and thus may be considered the safest to utilize when performing endoscopic or two incision CTR. FDSL is a reliable landmark to utilize in patients when no PL is present, but caution is advised as the safe zone is only slightly beyond 2 mm when a 2 standard deviation criteria is observed.

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