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Case Discussion: Fracture Through Accessory Navicular

Miss G is a 23 year old veterinary nurse who was in a car accident one year prior to her presentation to Dr Touzell. She described a moderate-speed accident and described an aggressive twisting motion to her right foot. She initially presented to her local General Practitioner, and screening x-rays did not demonstrate a fracture nor other injury to her foot.

Three months post injury, Miss G had ongoing pain in the medial border of her right foot. A CT performed three months after the accident (figure 1) demonstrated an accessory navicular but no fracture was reported. Miss G saw a local podiatrist who very appropriately trialled a period of offloading with a CAM boot for six weeks. This helped initially and Miss G was almost pain-free, but the pain recurred when the boot was removed. A form-fit medial arch support was then trialled, but Miss G still had pain when standing for more than thirty minutes and was unable to walk for more than ten minutes. Shock-wave therapy was also attempted but Miss G was unable to tolerate the pain associated with this.

MRI image of the foot

Miss G was then referred to a sports physician. An MRI was done which demonstrated increase in signal on T2 images at the synchondrosis of the accessory navicular, as well as some inflammation within the sinus tarsi. An injection of local anaesthetic and steroid into the sinus tarsi was done in an attempt to give Miss G some pain relief prior to an overseas holiday. On return, Miss G was still struggling to walk because of pain and was subsequently referred to Dr Touzell for review.

On examination, Miss G had normal hindfoot alignment and was unable to perform a single leg heel raise due to pain. She had point tenderness over the navicular tuberosity. Her tibialis posterior tendon had normal strength, but resisted inversion was painful. There was an obvious, tender bony bump medially.

Miss G was diagnosed with a fracture through the synchondrosis of her accessory navicular, and the decision to proceed with surgery was made given she had exhausted her non-operative management options. Via a small medial incision, the accessory navicular was identified and removed (figure 2), and the tibialis posterior tendon was carefully re-attached to the remaining navicular body. The procedure was uncomplicated. She was partially weight bearing in a CAM boot with a form-fit orthotic to support her medial longitudinal arch, then commenced fully weight bearing six weeks after surgery.

Excised accessory navicular

Six months after surgery, she has been able to work full-time as a veterinary nurse without pain. She still has some discomfort when running or when performing high-impact activities, but did not run for exercise prior to her injury. She is able to walk, wear most shoes (except high heels) and is able to participate in a gym program.

Key Learning Points:

  • An accessory navicular bone ('os naviculare') is a common condition present in approximately20% of the population (see Leonard 2010, below)

  • It can become inflamed spontaneously or as a result of trauma, causing medial sided foot pain

  • Offloading via CAM boot for six weeks is appropriate initial management

  • Surgical excision and tibialis posterior tendon re-attachment is a reliable procedure should non-operative intervention not be successful

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