Citation: Ferre-Martinez, A.; Miguel-Pérez, M.; Möller, I.; Ortiz-Miguel, S.; Pérez-Bellmunt, A.; Ruiz, N.; Sanjuan, X.; Agullo, J.; Ortiz-Sagristà, J.; Martinoli, C. Possible Points of Ulnar Nerve Entrapment in the Arm and Forearm: An Ultrasound, Anatomical, and Histological Study. Diagnostics 2023, 13, 1332. https://doi.org/10.3390/ diagnostics13071332 Academic Editors: Anna ˙ Zurada and Mario Manto Received: 7 February 2023 Revised: 21 March 2023 Accepted: 31 March 2023 Published: 3 April 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). diagnostics Article Possible Points of Ulnar Nerve Entrapment in the Arm and Forearm: An Ultrasound, Anatomical, and Histological Study Andrea Ferre-Martinez 1,† , Maribel Miguel-Pérez 1, * ,† , Ingrid Möller 1 , Sara Ortiz-Miguel 1,2 , Albert Pérez-Bellmunt 2 ,Núria Ruiz 1,3 , Xavier Sanjuan 3,4 , Jose Agullo 1 , Juan Ortiz-Sagristà 5 and Carlo Martinoli 6 1 Unit of Human Anatomy and Embryology, Department of Pathology and Experimental Therapeutics, Faculty of Medicine and Health Sciences (Bellvitge Campus), University of Barcelona, 08907 Barcelona, Spain 2 Basic Sciences Department, Universitat Internacional de Catalunya, 08017 Barcelona, Spain 3 Department of Pathology, University Hospital of Bellvitge, 08907 Barcelona, Spain 4 Unit of Pathological Anatomy, Department of Pathology and Experimental Therapeutics, Faculty of Medicine and Health Sciences (Bellvitge Campus), University of Barcelona, 08907 Barcelona, Spain 5 Anesthesiology Department, Fundació Puigvert, 08025 Barcelona, Spain 6 Cattedra di Radiologia “R”-DICMI, Universita di Genova, 16126 Genoa, Italy * Correspondence: mabelmig@gmail.com; Tel.: +34-93-402-0170 † These authors contributed equally to this work. Abstract: Background: Ulnar nerve entrapment is one of the most common entrapment neuropathies, usually occurring in the cubital tunnel of the elbow and in Guyon’s canal of the wrist. However, it can also occur at other anatomical locations. Purpose: Our aim was to review other possible locations of ulnar nerve entrapment in an ultrasound and anatomical study. Material and Methods: Eleven upper limbs from eight adult corpses were ultrasonographically examined and subsequently dissected in a dissection laboratory. Four specific anatomical points were analysed, and any anatomical variations were documented. Moreover, six samples of the nerve were taken for histological analysis. Results: Distinct anatomical relationships were observed during ultrasound and dissection between the ulnar nerve and the medial intermuscular septum, the triceps aponeurosis, Osborne’s fascia at the elbow, the arcuate ligament of Osborne and the intermuscular aponeurosis between the flexor carpi ulnaris and the flexor digitorum superficialis muscles. A statistical study showed that these locations are potential areas for ulnar nerve compression. In addition, a fourth head of the triceps brachii muscle was found in some specimens. Conclusion: Results demonstrate that ultrasound is a good tool to investigate ulnar nerve entrapment neuropathy and to identify other anatomical points where the nerve can remain compressed. Keywords: ulnar nerve; nerve entrapment; compressive neuropathy; ultrasound; intermuscular septum; muscular fascia; flexor carpi ulnaris; flexor digitorum superficialis 1. Introduction Entrapment neuropathies are a heterogeneous group of conditions in which periph- eral nerves are chronically compressed or stretched as a result of congenital or acquired disorders or a combination of both [1]. Clinical symptoms depend on the degree and duration of entrapment. They can range from sensory abnormalities (pain, paraesthesia, and numbness) to motor weakness in the area innervated by the affected nerve [2–4]. For this reason, accurate clinical evaluations including history taking, physical examinations, and electrodiagnostic tests are the mainstays of diagnosis. However, imaging studies have an important role in identifying the abnormality causing the entrapment neuropathy [2]. As for mononeuropathies, ulnar neuropathy is most often due to compression at different fibro-osseous tunnels locations as the cubital tunnel of the elbow and the Guyon’s canal of the wrist [4,5] or congenital conditions involving accessory muscles [1]. However, Diagnostics 2023, 13, 1332. https://doi.org/10.3390/diagnostics13071332 https://www.mdpi.com/journal/diagnostics