Accessory navicular syndrome
Persistent medial midfoot pain for two years which worsened on prolonged walking
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A type 2 os naviculare is seen in this teenager. It is the commonest type and is triangular in shape with a clearly definable articular cartilage margin with the adjacent navicular bone. There is edema along the articular margin with mild fluid in the tibialis posterior tendon sheath immediately proximal to the os.
This condition is more common in women, and especially in adolescents. When these patients come to clinic, they point directly to the posteromedial aspect of the midfoot, overlying the os naviculare, making the diagnosis straightforward.
This patient had a radiograph done two years previously and the abnormality was not reported. I did not arrange a repeat radiograph, instead proceeding straight to MRI, which also allowed other internal derangements to be excluded.
If you look carefully, you will also notice an increased prominence of the lateral process of the calcaneal tuberosity. It is important to understand the role of the plantar arches of the foot and the mechanism of movement. The presence of this os introduces changes to the patient's weight-bearing patterns and treatment involves muscle strengthening exercises, with analgesia when overuse pain worsens.
In cases where the resultant functional impairment overly restricts ADLs, surgical corrective options are available.