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http://upload.orthobullets.com/topic/4066/images/clinical photo - courtesy Miller_moved.png
http://upload.orthobullets.com/topic/4066/images/Neutral lateral xray - courtesy Miller_moved.png
http://upload.orthobullets.com/topic/4066/images/plantar flexion lateral xray - courtesy Miller_moved.png
http://upload.orthobullets.com/topic/4066/images/Meary's angle_moved.png
Introduction
  • Irreducible dorsal dislocation of the navicular on the talus producing a rigid flatfoot deformity
  • Epidemiology:
    • Rare, 1:150,000 births
    • 50% associated with neuromuscular disease or chromosomal aberrations  
      • Myelomeningocele
      • Arthrogryposis
      • Diastematomyelia
  • Pathoanatomy
    • rigid foot deformity
      • irreducible dorsolateral navicular dislocation
      • vertically oriented talus
      • calcaneal eversion with attenuated spring ligament
    • soft tissue contractures
      • displacement of peroneal longus and posterior tibilais tendon so they function as dorsiflexors rather than plantar flexors
      • contracture of the Achilles tendon
  • Genetics
    • a positive family history is present in up to 20% of patients
  • Prognosis 
    • poor in untreated cases and associated with significant disability
  • Differential diagnosis
    • oblique talus
      • anatomic variant
        • talonavicular subluxation that reduces with forced plantarflexion of the foot
      • treatment 
        • typically consists of observation and shoe inserts
        • some require surgical pinning of the talonavicular joint and achilles lengthening for persistent subluxation
Presentation
  • Physical exam
    • rigid rockerbottom deformity
      • fixed hindfoot equinovalgus 
        • due to contracture of the Achilles and peroneal tendons
      • rigid midfoot dorsiflexion
        • secondary to the dislocated navicular
      • forefoot abducted and dorsiflexed
        • due to contractures of the EDL, EHL and tibialis anterior tendons
    • prominent talar head
      • can be palpated in medial plantar arch on exam
        • produces a convex plantar surface
    • gait abnormality
      • patient may demonstrate a "peg-leg" or a calcaneal gait due to poor push-off power 
      • limited forefoot contact, excessive heel contact
    • neurologic deficits
      • a careful neurologic exam needs to be performed due to frequent association with neuromuscular disorders
Imaging
  • Radiographs
    • recommended views
      • AP, oblique and lateral foot 
    • findings
      • lateral
        • vertically positioned talus & dorsal dislocation of navicular  q
          • line in long axis of talus passes below the first metatarsal-cuneiform axis
            • before ossification of navicular at age 3, the first metatarsal is used as a proxy for the navicular on radiographic evaluation
      • AP
        • talocalcaneal angle > 40° (20-40° is normal) 
    • alternative views
      • forced plantar flexion lateral radiograph is diagnostic 
        • shows persistent dorsal dislocation of the talonavicular joint 
          • oblique talus reduces on this view
          • Meary's angle > 20° (between line of longitudinal axis of talus and longitudinal axis of 1st metatarsal)  
        • forced dorsiflexion lateral
          • reveals fixed equinus
  • MRI 
    • neuraxial imaging should be performed to rule out neurologic disorder
Differential Diagnosis
  • Oblique talus 
    • reduces with forced plantar flexion
    • treatment is observation vs casting
  • Calcaneovalgus foot deformity
  • Tarsal coalition
  • Paralytic pes valgus
  • Pes planovalgus
Treatment
  • Nonoperative
    • serial manipulation and casting for three months 
      • indications
        • indicated preoperatively to stretch the dorsolateral soft-tissue structures q
      • typically followed by surgical release and pinning of the talonavicular joint with percutaneous achilles tenotomy
  • Operative
    • surgical release and talonavicular reduction and pinning  q
      • indications
        • indicated in most cases
        • performed at 12-18 months of age
      • technique
        • involves pantalar release with concomitant lengthening of peroneals, Achilles, and toe extensors 
        • talonavicular joint is reduced and pinned while reconstruction of the plantar calcaneonavicular (spring) ligament is performed 
        • concomitant tibialis anterior transfer to talar neck
    • minimally invasive correction
      • indications
        • new technique performed in some centers to avoid complications associated with extensive surgical releases
      • technique
        • principles for casting are similar to the Ponseti technique used clubfoot
        • serial casting utilized to stretch contracted dorsal and lateral soft tissue structures and gradually reduced talonavicular joint
        • once reduction is achieved with cast, closed or open reduction is performed and secured with pin fixation 
        • percutaneous achilles tenotomy is required to correct the equinus deformity
    • talectomy
      • indicated in resistant case
    • triple arthrodesis
      • as salvage procedure
Complications
  • Missed vertical talus
    • reconstructive options are less predictable after age 3, and patients may require triple arthrodesis as salvage procedure
 

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