Os cuboideum secundarium: A rare accessory ossicle with the potential to mimic a mass on magnetic resonance imaging

Accessory ossicles are common incidental findings on radiographs of the ankle and foot. While typically asymptomatic and of no clinical significance, they are sometimes associated with local pain or even mistaken for pathological conditions such as fractures. Given the potential for misinterpretation, it is important to understand their typical locations and appearances. This case highlights an exceptionally rare accessory ossicle called the os cuboideum secundarium, located adjacent to the cuboid and calcaneus. Interestingly, this case demonstrates the potential for this rare ossicle to mimic a mass on magnetic resonance imaging (MRI). Furthermore, despite the significant improvements in the understanding of musculoskeletal pathology afforded by advancements in cross-sectional imaging techniques, this case is a reminder of certain pitfalls that remain. Lastly, it highlights the importance of radiographs as an initial diagnostic study in evaluating foot pain.