Accessory Navicular

  • Most common accessory bone of the foot
  • Located at Medial plantar border of the navicular
  • Associated with Tibialis Posterior tendon
  • Accessory ossicles are derived from unfused ossification centres
  • Synonyms: Os tibiale; Os tibiale externum; Naviculare secundum

Incidence

  • 21% incidence; 89% of cases are bilateral
  • One of the most common accessory ossicles in the foot It is seen over the medial pole of the navicular bone, usually in adolescent patients
  • It is most commonly symptomatic in the 2nd decade of life and causes medial foot pain
  • <1% of patients become symptomatic.
  • Usually affects teens and young adults
  • More frequent in females

Aetiology

  • variant of normal anatomy.
  • It may become symptomatic from the bony prominence impinging against shoe wear.
  • The patient may have diffuse medial and plantar arch pain.
  • It may cause problems by destabilizing the insertion and diminishing the pull of the PTT.
  • In patients with associated severe flatfoot deformity, lateral pain may occur secondary to impingement of the calcaneus against the fibula.
  • A traumatic event can cause injury to the fibrocartilaginous synchondrosis that attaches the ossicle to the main navicular.

Associated Conditions

  • Flatfoot deformity
  • Secondary Achilles tendon contracture

Symptoms

  • Considered an incidental finding on radiographs, but may become symptomatic
  • bursa, redness, irritation, local tenderness
  • Often presents in adolescent patients or young adults, with flatfoot deformity and arch pain

Classification

3 major types of accessory navicular adjacent to the posteromedial navicular tuberosity

Type DescriptionIncidence
ISmall, 2 – 3 mm sesamoid bone in the PTT (os tibiale externum)~30%
IILarger ossicle than type I
Secondary ossification centre of the navicular bone		~50%
IIIEnlarged navicular tuberosity (cornate navicular)
considered a fused variant of a type II, often with pointed shape		~20%
Classification of Accessory Navicular

X-ray

Accessory Navicular, dorsoplantar radiograph showing an accessory navicular and a cornuate navicular
Dorsoplantar radiograph showing an accessory navicular and a cornuate navicular. Image by Mikael Häggström, Wikimedia Commons, CC0.
  • AP, Lat & 45 degree eversion oblique
  • Navicular is the last tarsal bone to ossify from multiple ossification centres
  • Females – 1-3.5 yr
  • Male – 3.0- 5.5 yr
  • Smooth margins with well-formed cortex differentiate this condition from acute fracture
  • There is no evidence that the longitudinal arch is any different, essentially an incidental finding

Bone Scan

  • May show increased activity over an accessory navicular
  • May be needed if a navicular stress fracture is suspected in the differential diagnosis

MRI

  • Useful when plain films are unremarkable
  • Often, a type-II accessory navicular is attached to the tuberosity by a fibrocartilage or hyaline cartilage layer, and MRI may show soft-tissue oedema consistent with a synchondrosis sprain or tear.
  • Altered signal intensity and bone marrow oedema, suggestive of chronic stress and/or osteonecrosis
  • Also helpful in showing PTT degeneration

Differential Diagnosis

  • Navicular fracture may mimic an acute avulsion fracture of the tuberosity of the navicular.
  • Posterior tibial tendinitis
  • Stress fracture of navicular

Treatment

  • Most patients are asymptomatic or are successfully managed conservatively
    • rest and avoid athletics or aggravating activities.
    • Anti-inflammatory medication
    • Shoe-wear modification
      • use of a softer, wider shoe
      • If flatfoot is present, a medial arch support may be useful, but often the patient may not tolerate it because of direct pressure on the ossicle.
    • Below-the-knee walking cast or removable fracture boot may be used for 3-6 weeks for persistent symptoms.
    • Physiotherapy – strengthening exercises
  • Surgical
    • Rarely simple surgical excision
      • Options
        1. Kidner procedure, the accessory navicular is excised, and the PTT is rerouted into a more plantar position
        2. excision of the ossicle and reattachment of the PTT insertion to the navicular, with suture anchors or sutures passed through drill holes
    • Severe flatfoot deformity with lateral impingement symptoms
      • may require concomitant osteotomy of the calcaneus and/or medial column of the foot to improve alignment and decrease mechanical stress of the PTT insertion.

Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.