Use of malleoli as an indicator for flatfoot in patients with Down syndrome: development of a simple and non-invasive evaluation method through medial longitudinal arch

[Purpose] Flatfoot often presents in patients with Down syndrome, and it can be diagnosed using a simple radiograph. Consequently, due to radiograph limitations, alternative non-invasive testing must be determined. Conventionally, arch height ratio can be used for evaluation of the medial longitudinal arch, where the foot is evaluated by detecting the navicular bone on the foot surface. However, detection of the navicular tuberosity is difficult and even though the detection is relatively straightforward for patients without intellectual disability, measuring navicular bone is more difficult in patients with intellectual disability, such as those who have Down syndrome and are uncooperative with a tester. Therefore, we evaluated arch height ratio using the malleoli instead of the navicular bone to determine whether malleoli testing was appropriate for patients with Down syndrome that have an intellectual disability. [Participants and Methods] We conducted a retrospective study of 16 pairs of feet in 16 patients with Down syndrome, diagnosed with flatfoot. The height to the centre of the talo-navicular joint and that of the malleoli from the sole were measured on radiographs using weight-bearing conditions. [Results] The age range was 5.2 to 25.3 years. There was a correlation between the height of the navicular bone and that of the medial and lateral malleoli. [Conclusion] We conclude that the medial and lateral malleoli can substitute navicular bone as a landmark diagnosis test for flatfoot. Considering the close physical distance between the medial malleolus and navicular bone, and the association between the tibia and medial longitudinal arch, the medial malleolus may provide a better landmark in patients with Down syndrome with it being potentially less invasive for uncooperative patients.