Muscle variants of the upper and lower limb (with anatomical correlation).

Several accessory muscles in the upper and lower limb have been described in the medical literature. Most are asymptomatic and represent incidental findings at imaging. In some instances, however, these muscles may become clinically relevant producing palpable swelling, entrapment of neurovascular structures, or exercise-related pain. The diagnosis of accessory muscles is based on recognition of their typical location and on cross-sectional imaging features. Familiarity with their most common location and knowledge of the possible clinical syndromes caused by these supernumerary structures may aid in diagnosis and treatment.