Problems with a Type II Accessory Navicular

The type-II accessory navicular bone is an accessory ossification center that is connected to the navicular proper by a fibrocartilaginous synchondrosis. The posterior tibial tendon attaches to the type-II accessory navicular instead of the navicular tuberosity.

While most people with a type II accessory navicular are asymptomatic, some present with problems related to this bone. These include:

• Flat-foot deformity: Attachment of the posterior tibial tendon to the Type II accessory navicular may lead to straightening of the tendon, causing adduction forces.
• Tendinosis/Tear: Can occur due to increased stress caused by decreased leverage of the medial malleolus on the tendon from a more proximal insertion. Prevalence of type-II accessory navicular bones in patients with posterior tibial tendon dysfunction is higher than in the general population.
• "Symptomatic accessory navicular": Due to repetitive shearing stress forces acting on the type-II accessory navicular synchondrosis. Resultant bone remodeling may result in osteonecrosis surrounding the synchondrosis. MRI will reveal bone marrow signal abnormalities in the accessory navicular and navicular proper adjacent to the synchondrosis.

References

• Bernaerts A, Vanhoenacker FM, Van de Perre S, De Schepper AM, Parizel PM. Accessory navicular bone: not such a normal variant. JBR-BTR. 2004 Sep-Oct;87(5):250-2.
• Mellado JM, Ramos A, Salvadó E, Camins A, Danús M, Saurí A. Accessory ossicles and sesamoid bones of the ankle and foot: imaging findings, clinical significance and differential diagnosis. Eur Radiol. 2003 Dec;13 Suppl 6:L164-77.
• Miller TT, Staron RB, Feldman F, Parisien M, Glucksman WJ, Gandolfo LH. The symptomatic accessory tarsal navicular bone: assessment with MR imaging. Radiology. 1995 Jun;195(3):849-53.