American Association for Hand Surgery
Theme: Beyond Innovation

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Patterns of Ulnar Nerve Arborization in the Palm: Clinical Implications for Nerve Decompression in the Hand and Wrist
Svenna HWL Verhiel, MD1; Daphne van Hooven, BSc1; Rohit Garg, MD1; Rachel EW Gottlieb, BSc1; Marco JPF Ritt, MD, PhD2; Neal C Chen, MD3; Kyle R Eberlin, MD1
1Massachusetts General Hospital / Harvard University, Boston, MA, 2VU Medical Center, Amsterdam, Netherlands, 3Massachusetts General Hospital, Boston, MA

Introduction Understanding the variations in arborization pattern and communicating branches is important for diagnosis and for surgical planning of carpal tunnel and/or Guyon's canal decompression, as there may be an increased risk to the ulnar and/or median nerve branches if appropriate care is not taken during surgery. The purposes of this study were to examine variations and frequencies of the arborization patterns and communicating branches of the ulnar nerve in the palm, to review existing literature, and to relate these findings to nerve decompression in the hand and wrist.
Methods & Materials The arborization pattern of the ulnar nerve near Guyon's canal was examined in 18 cadavers, and described according to the classification of Murata et al. Communicating branches between the ulnar nerve and the median nerve were described according to the classification by Bas & Kleinert. The specific distance from the wrist flexion crease to the origin of the communicating branch and the angle of the communicating branch with the originating nerve were measured.
Results In 13 of 18 (72%) cadavers, a type 1 arborization pattern was found; in 4 (22%) cadavers, a type 2 was found; and in 1 cadaver (6%), a branching pattern not previously described was found (Table 1). In 11 of 18 (61%) cadavers, a communicating branch between the ulnar and median nerve was observed. The branch ran from the ulnar to the median nerve (type 1) in 10 (56%) cadavers, the connection was plexiform (type 4) in 1 (5.6%) cadaver. The communicating branch originated at a median distance of 1mm from the distal edge of the transverse carpal ligament and had a median angle of 42.5 degrees (IQR 40-45) (Figure 1).
Conclusions Variations in arborization patterns of the ulnar nerve and existence of communicating branches between the ulnar and median nerve in the palm are common and may lead to atypical distribution of symptoms and unforeseen risks during hand surgery. Knowledge about variations in arborization patterns of the ulnar nerve and communicating branches between the ulnar and median nerve in the palm optimizes diagnoses and minimizes specific surgical risks in hand surgery.


Figure 1: Communicating branches from the ulnar to the median nerve and its relationship to the transverse carpal ligament.


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