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Tibialis Posterior at Accessory Navicular

tendo tibialis posterioris ad os naviculare accessorium

When an accessory navicular (os naviculare accessorium) is present — in approximately 10-14% of individuals — the tibialis posterior tendon may insert predominantly into the accessory bone rather than the main navicular, altering the mechanical advantage and the medial arch support provided by the TPT. Three types are recognised: Type I (sesamoid within TPT), Type II (synchondrosis to navicular, most symptomatic), and Type III (fused os naviculare cornuatum).

Region: Foot & Ankle

Clinical Relevance

Clinical Notes

Type II accessory navicular syndrome produces medial midfoot pain at the navicular prominence, worsened by activity, in adolescents and young adults. The synchondrosis between the accessory and the navicular is the site of stress injury and pain. The altered TPT insertion into the accessory bone rather than the navicular may contribute to longitudinal arch dysfunction and pes planus. Treatment is conservative with orthotics and activity modification; Kidner procedure (excision of the accessory navicular with TPT reinsertion onto the navicular) provides surgical correction for refractory cases.

Pathology

Common Injuries & Conditions

Accessory Navicular Syndrome Type II

A symptomatic Type II accessory navicular produces medial midfoot pain and a painful bony prominence at the navicular; the synchondrosis stress injury is confirmed by MRI showing bone marrow oedema at the junction, managed by orthotics, immobilisation, or Kidner procedure excising the accessory bone and advancing the TPT.