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https://upload.orthobullets.com/topic/4070/images/xray - lateral - wheeless_moved.jpg
https://upload.orthobullets.com/topic/4070/images/seasmoid navicular.jpg
https://upload.orthobullets.com/topic/4070/images/incomplete pic 1.jpg
https://upload.orthobullets.com/topic/4070/images/complete pic .jpg
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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Questions (4)
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(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? Review Topic

QID: 1021
FIGURES:
1

No treatment needed-return to class

1%

(24/3600)

2

Continue serial casting

1%

(27/3600)

3

Excision of the medial prominence of the navicular, including the synchondrosis

95%

(3418/3600)

4

ORIF of the navicular non-union

3%

(98/3600)

5

Bone stimulator for the navicular non-union

0%

(12/3600)

Select Answer to see Preferred Response

PREFERRED RESPONSE 3

(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? Review Topic

QID: 546
FIGURES:
1

Total contact cast

2%

(36/1772)

2

Steroid injection

1%

(21/1772)

3

MRI of the foot and chest CT scan

1%

(15/1772)

4

Open biopsy

1%

(9/1772)

5

Surgical excision

95%

(1688/1772)

Select Answer to see Preferred Response

PREFERRED RESPONSE 5
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