Thoracic outlet syndrome is a group of disorders that affect the upper extremity and neck, resulting in compression of the neurovascular bundle that exits the thoracic outlet. Depending on the type of compressed structure, the arterial, venous, and neurogenic forms of TOS are distinguished. In some populations, e.g., in certain groups of athletes, some sources report incidence rates as high as about 80 cases per 1000 people, while in the general population, it is equal to 2–4 per 1000. Although the pathogenesis of this condition appears relatively simple, there are a very large number of overlapping risk factors that drive such a high incidence in certain risk groups. Undoubtedly, a thorough knowledge of them and their etiology is essential to estimate the risk of TOS or make a quick and accurate diagnosis.

Purpose: Like other muscular compartments of the human body, the intrinsic muscles of the foot present considerable morphological variability. The aim of this review was to present variations that can potentially cause problems during surgery but might be detected during an ultrasound examination. Materials and methods: PubMed was searched for relevant articles. The identified papers were listed, and citation tracking was performed. Results: Even though lower limb structure is well studied, the variations associated with the intrinsic muscles of the foot and their related ultrasound examination are not. Conclusions: The muscles and tendons of the foot demonstrate similar degrees of variance as other regions of the human body; however, this subject is not as widely covered in the literature. Further ultrasound studies are needed to build awareness of morphological variability in this region, as the findings could prevent misdiagnosis.