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http://upload.orthobullets.com/topic/4070/images/xray - lateral - wheeless_moved.jpg
http://upload.orthobullets.com/topic/4070/images/seasmoid navicular.jpg
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Introduction
  • Epidemiology
    • incidence 
      • accessory navicular is a normal variant seen in up to 12% of population
      • majority of patients are asymptomatic
    • demographics
      • more commonly symptomatic in females
  • Pathophysiology
    • pathoanatomy
      • occurs as a plantar medial enlargement of the navicular bone
      • exists as accessory bone or as completely ossified extension of the navicular
  • Genetics
    • inheritance pattern
      • autosomal dominant
  • Associated conditions
    • flat feet 
    • posterior tibial tendon insufficiency 
Anatomy
  • Osteology
    • navicular bone normally has a single center of ossification
      • ossifies at age 3 in girls and 5 in boys and fuses at 13 years of age
    • an accessory navicular is a normal variant from which the tuberosity of the navicular develops from a secondary ossification center that fails to unite during childhood
      • the accessory navicular does not begin to ossify prior to age 8
  • Muscles
    • tibialis posterior inserts onto the tuberosity (medial) of the navicular bone 
      • innervated by tibial nerve 
  • Ligament
    • plantar calcaneonavicular (spring) ligament originates from sustentaculum tali and inserts on to navicular
      • plantar support for head of talus
    • bifurcate ligament attaches the anterior process of the calcaneus to the navicular and cuboid bones
      • lateral support
    • dorsal talonavicular ligament connects the neck of the talus to the dorsal surface of the navicular bone
      • dorsal support
  • Blood Supply
    • dorsalis pedis artery (dorsal aspect)
    • medial plantar artery (plantar aspect)
    • anastomosis between dorsalis pedis and medial plantar arteries (medial surface of tuberosity)
Classification
 
Radiographic Classification 
Type 1 Sesamoid bone in the substance of the tibialisposterior insertion  
Type 2 Separate accessory bone attached to native navicular via synchondrosis
 
Type 3 Complete bony enlargement   
 
Presentation
  • Symptoms
    • asymptomatic
      • majority of patients are asymptomatic 
    • medial arch pain
      • often worse with overuse
      • due to repeated microfracture at the synchondrosis or from inflammation of the posterior tibialis tendon insertion
  • Physical exam
    • inspection
      • may have swelling in region
      • medial foot tenderness
        • firm and tender at the medial and plantar aspect of the navicular bone
Imaging
  • Radiographs
    • recommended views
      • AP, lateral, external obliques    
        • best seen with an external oblique view
    • findings
      • will see bony enlargement or accessory bone
  • MRI
    • indications
      • evaluation for other pathology 
Treatment
  • Nonoperative
    • activity restriction, shoe modification, and non-narcotic analgesics
      • indications
        • first-line of treatment
      • modalities
        • the use of arch supports or pads over the bony prominence may be helpful
        • a UCBL orthosis may invert the heel during walking and decrease symptoms
        • orthotics must offload pressure from the accessory navicular or they will exacerbate symptoms
      • outcomes
        • most children and adolescents who have a symptomatic accessory tarsal navicular bone become asymptomatic when they reach skeletal maturity
    • short period of cast immobilization
      • indications
        • pain is refractory to activity modification and shoe modifications
  • Operative
    • excision of accessory navicular  
      • indication
        •  recalcitrant cases that have failed extended nonoperative management
Technique
  • Excision of accessory navicular
    • approach
      • medial approach to the foot
      • an incision is made from distal third of talus to medial cuneiform
      • identify the posterior tibialis and then reflect the tendon (either plantar or dorsal) 
    • resection technique
      • the synchondrosis between the accessory navicular and native navicular can typically be identified easily
      • resect the accessory navicular (a 1/4" curved osteotome may facilitate the resection) through the synchondrosis
      • trim down the body of the navicular (typically with osteotomes and rongeurs) to remove any medial prominence
      • resection is typically in line with medial border of the medial cuneiform
      • do NOT advance the posterior tibial tendon.  The advancement does not enhance the result and increases downtime and morbidity
    • flatfoot deformity correction
      • this is not performed concomitantly with the procedure unless the flatfoot is the primary pathology
Complications
  • Persistent medial prominence and pain
    • the most common complication is persistent medial prominence and pain when the body of the navicular is not trimmed sufficiently 
 

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