Intrinsic hand muscles play a fundamental role in tuning the fine motricity of the hand and may be affected by several pathologic conditions, including traumatic injuries, atrophic changes induced by denervation, and space-occupying masses. Modern hand surgery techniques allow to target several hand muscle pathologies and, as a direct consequence, requests for hand imaging now carry increasingly complex diagnostic questions. The progressive refinement of ultrasound technology and the current availability of high and ultra-high frequency linear transducers that allow the investigation of intrinsic hand muscles and tendons with incomparable resolution have made this modality an essential tool for the evaluation of pathological processes involving these tiny structures. Indeed, intrinsic hand muscles lie in a superficial position and are amenable to investigation by means of transducers with frequency bands superior to 20 MHz, offering clear advantages in terms of resolution and costs compared to magnetic resonance imaging. In addition, ultrasound allows to perform dynamic maneuvers that can critically enhance its diagnostic power, by examining the questioned structure during stress tests that simulate the conditions eliciting clinical symptoms. The present article aims to review the anatomy, the ultrasound scanning technique, and the clinical application of thenar, hypothenar, lumbricals and interossei muscles imaging, also showing some examples of pathology involving these structures.

Objective: The aim of the present study is to describe the ultrasound (US) and magnetic resonance imaging (MRI) findings in patients with neuropathies affecting the deep (DB) and superficial (SB) branches of the Ulnar nerve (UN) and to investigate the potential role of imaging modalities in the diagnostic workup of these conditions. Materials and methods: We screened our institutional imaging database to identify patients with a diagnosis of UN mononeuropathy, and among them, we reviewed the cases where US disclosed pathological findings affecting the UN terminal divisions. In this latter subgroup, we retrieved available data on MRI and electrodiagnostic tests performed by the patients during the diagnostic workup. All the patients were evaluated with US machines equipped with 17–5-MHz, 18–4-MHz, 24–8-MHz, or 22–8-MHz probes. MRI exams were performed on a 3-T unit equipped with a 64-channel head RF coil. Results: Among 166 patients with UN mononeuropathy, we retrieved 15 patients (9%) for which US detected pathological findings affecting the UN terminal divisions, consisting of 7 cases of DB neuropathy, 4 cases of SB neuropathy, and 4 cases of combined neuropathy involving both nerves. Seven (46.7%) patients were submitted to MRI to integrate US findings. Among patients with SB and DB neuropathies, imaging allowed the identification of 7 traumatic nerve injuries, 2 nerve tumors, and 6 entrapment neuropathies, including 4 cases of nerve compression by a ganglion cyst. Conclusion: High-resolution US and MRI are accurate modalities for the investigation of patients with SB/DB neuropathy, can provide critical information on the cause of nerve damage, and guide therapeutic decisions. Critical relevance statement: High-resolution US and MRI are accurate modalities for the investigation of patients with superficial/deep branch of the ulnar nerve neuropathy. In the proper setting, US may be regarded as a first-line approach in patients with suspected neuropathies affecting these small branches. Key points: • Neuropathies affecting the distal ulnar nerve often require multimodal investigations. • US and MRI can provide detailed morphological information about the terminal branches of the ulnar nerve. • US may be considered as a first-line approach in suspected distal ulnar nerve neuropathies. Graphical

Plantar intrinsic muscles play a pivotal role in posture control and gait dynamics. They help maintain the longitudinal and transverse arches of the foot, and they regulate the degree and velocity of arch deformation during walking or running. Consequently, pathologies affecting the plantar intrinsic muscles (for instance, acquired and inherited neuropathies) lead to foot deformity, gait disorders, and painful syndromes. Intrinsic muscle malfunctioning is also associated with multifactorial overuse or degenerative conditions such as pes planus, hallux valgus, and plantar fasciitis. As the clinical examination of each intrinsic muscle is challenging, ultrasound is gaining a growing interest as an imaging tool to investigate the trophism of these muscular structures and the pattern of their alterations, and potentially to follow up on the effects of dedicated rehabilitation protocols. The ten plantar intrinsic muscles can be dived into three groups (medial, central and lateral) and four layers. Here, we propose a regional and landmark-based approach to the complex sonoanatomy of the plantar intrinsic muscles in order to facilitate the correct identification of each muscle from the superficial to the deepest layer. We also summarize the pathological ultrasound findings that can be encountered when scanning the plantar muscles, pointing out the patterns of alterations specific to certain conditions, such as plantar nerves mononeuropathies.

Inflammatory neuropathies comprise a heterogeneous group of conditions united by inflammation-mediated damage to peripheral nerves and their vasa nervorum. Although classification, diagnosis and management are largely based on clinical features, electrodiagnostic and laboratory examinations, imaging studies play an important supporting role. Ultrasound and MRI are the two modalities used for imaging peripheral nerves. The two techniques differ in the clinical context of application, the information provided and the diagnostic performance. This narrative review aims to provide guidance on when and how to use ultrasound or MRI in patients with inflammatory neuropathies, highlighting their respective strengths and pitfalls, and how to combine these imaging modalities to enhance their usefulness in the diagnostic-therapeutic management of these far from rare conditions.

Objective: To validate high-frequency ultrasound as a valuable imaging modality in the assessment of the annular pulley system of the toes, describing their normal sonographic appearance and presenting some illustrative pathological cases. Materials and methods: The first phase of this observational study involved examining the annular pulley system of the flexor tendons of the toes in a series of cadaveric specimens, testing the ability of ultrasound to recognize these structures. In the second phase, two expert sonographers examined a sample of 15 healthy adult participants using two different 18–5 MHz and 24–8 MHz linear array ultrasound probes. Sonographic visibility, position, and maximal thickness of each annular pulley were assessed. Results: In the cadaveric study, ultrasound provided identification of 4 annular pulleys in the lesser toes and 3 in the great toe across 8 feet from 4 cadavers. In 30 feet of 15 healthy participants, ultrasound was able to consistently recognize and measure the annular pulleys of toes I–IV, with minimal variability between operators. The V toe annular pulleys were less reliably visualized. The intraclass correlation coefficient (ICC) analysis of pulley maximal thickness measurements between the two sonographers showed moderate agreement for the 24–8 MHz probe with a mean ICC of 0.393 (CI: 0.315–0.471) and better agreement for the 18–5 MHz probe with a mean ICC of 0.529 (CI: 0.442–0.616). Conclusion: This study provides a comprehensive description of the sonoanatomy of the annular pulleys of the flexor tendons in the toes and demonstrates the potential of ultrasound as a valuable tool for diagnosing pathologies of these structures.