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Accessory Navicular

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Topic updated on 08/09/16 12:55pm
Introduction
  • Epidemiology
    • incidence 
      • accessory navicular is a normal variant seen in up to 12% of population
        • majority of patients are asymptomatic
          • 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
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 tibialis posterior insertion
Type 2 Separate accessory bone attached to native navicular via synchondrosis

Type 3 Complete boney enlargement

 

Presentation
  • Symptoms
    • medial arch pain that is worse with overuse
      • due to repeated microfracture at the synchondrosis or from inflammation of the posterior tibialis tendon insertion
  • Physical exam
    • inspection
      • swelling
      • 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
      • to help delineate insertion of tibialis posterior tendon 
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 boney prominence may be helpful
        • a UCBL orthosis may invert the heel during walking and decrease symptoms
      • outcomes
        • nearly all 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
    • technique
      • bone should be resected flush with the medial cuneiform
        • most common cause of persistent symptoms after surgery is inadequate bone resection
        • other patients may have persistent pain from scar tissue or other causes
      • may need to split the posterior tibialis tendon in order to excise the navicular
      • re-routing the posterior tibialis will not correct flatfoot deformity
      • calcaneus osteotomy if flatfoot correction is needed

 

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Qbank (3 Questions)

TAG
(OBQ08.160) An 18-year-old male complains of a painful prominence over his medial midfoot for the past 2 years; NSAIDs and orthotics have failed to provide relief. Physical exam demonstrates a firm, nonmobile, tender bump on the medial midfoot with no skin changes. A radiograph is provided in figure A. Which of the following is the best treatment option? Topic Review Topic
FIGURES: A          

1. Total contact cast
2. Steroid injection
3. MRI of the foot and chest CT scan
4. Open biopsy
5. Surgical excision

PREFERRED RESPONSE ▶
TAG
(OBQ05.135) A 10-year-old boy presents with medial foot pain that is severe enough that it limits his daily activities such as walking to school. Physical exam shows tenderness in the medial forefoot 3 cm anterior and inferior to the medial malleolus. A radiograph is shown in Figure A. Nonoperative treatment including orthotics and cast immobilization was attempted for three months without success. What is the most appropriate next step in treatment? Topic Review Topic
FIGURES: A          

1. No treatment needed-return to class
2. Continue serial casting
3. Excision of the medial prominence of the navicular, including the synchondrosis
4. ORIF of the navicular non-union
5. Bone stimulator for the navicular non-union

PREFERRED RESPONSE ▶



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