Congenital Absence of the Navicular Bone: A Rare Cause of Adult-Acquired Flatfoot and Posterior Tibial Tendon Dysfunction.

The navicular bone is critical for foot biomechanics, stabilizing the midfoot through its articulation with the talus and cuneiform bones. Variations, including accessory ossicles, hypoplasia, and complete absence, can lead to altered foot function. We present the case of a 58-year-old female patient who experienced persistent left foot pain. Imaging revealed the congenital absence of the navicular bone, resulting in altered biomechanics, midfoot instability, flatfoot deformity, and secondary degenerative changes. Posterior tibial tendon dysfunction (PTTD), a leading cause of adult-acquired flatfoot, is exacerbated by navicular anomalies. Advanced imaging plays a critical role in diagnosis, with treatment ranging from conservative management to surgery, depending on severity.