Ultrasound of the plantar foot: a guide for the assessment of plantar intrinsic muscles

Federico Zaottini1, Riccardo Picasso1, Federico Pistoia1, Maribel Miguel Perez2, Deborah Bianco3, Rinaldi Simone3, Gabriele Rossi3, Marta Macciò3, Michelle Pansecchi3, Luca Tovt3, Carlo Martinoli1,3

Affiliation and address for correspondence
J Ultrason 2023;23: e151–e160
DOI: 10.15557/JoU.2023.0024
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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.

hallux valgus; plantar; fasciitis; muscular atrophy; ultrasonography