Updated: 1/18/2021

Tarsal Coalition

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Introduction
  • Structural anomaly between two or three tarsal bones causing a rigid flatfoot 
    • two types
      • congenital
        • most common
      • acquired
        • less common and caused by
          • trauma
          • degenerative 
          • infections
  • Epidemiology 
    • demographics
      • age of onset
        • calcaneonavicular usually 8-12 years old 
        • talocalcaneal usually 12-15 years old
    • prevalence 
      • varies from 1%-2%
    • location
      • calcaneonavicular (most common)
      • talocalcaneus 
  • Pathophysiology  
    • embryology
      • failure of mesenchymal segmentation leading to coalition between two or three tarsal bones 
        • develops into a fibrous coalition, or undergoes metaplasia to cartilage +/-  bone
    • pathoanatomy
      • gait mechanics
        • subtalar joint will normally rotate 10 degrees internally during stance phase
          • in presence of coalition, internal rotation does not occur
      • deformity
        • flattening of longitudinal arch
        • abduction of forefoot
        • valgus hindfoot
        • peroneal spasticity (also known as peroneal spastic flatfoot)
      • pain generator theories
        • ossification of previously fibrous or cartilaginous coalition
        • microfracture at coalition bone interface
        • secondary chondral damage or degenerative changes
        • increased stress on other hindfoot joints
  • Associated conditions
    • nonsyndromic
      • autosomal dominant
    • syndromic
      • fibular hemimelia
      • carpal coalition
      • FGFR-associated craniosynostosis (FGFR-1, FGFR-2, FGFR-3)
      • Apert syndrome, Pfeiffer, Crouzon, Jackson-Weiss and Muenke
Classification
  • Anatomic classification
    • calcaneonavicular 
      • between calcaneus and navicular bones (most common)
    • talocalcaneal            
      • middle facet of talocalcaneal joint
  • Pathoanatomic classification
    • 3 types
      • fibrous coalition (syndesmosis)
      • cartilagenous coalition (synchondrosis)
      • osseous coalition (synostosis)
Presentation
  • History
    • history of prior recurrent ankle sprains 
  • Symptoms
    • asymptomatic
      • most coalitions are found incidentally
      • 75% of people are asymptomatic
    • pain
      • location of pain
        • sinus tarsi and inferior fibula suggests calcaneonavicular 
        • distal to medial malleolus or medial foot suggests talocalcaneal 
      • pain worsened by activity
        • onset of symptoms correlates with age of ossification of coalition
      • calf pain
        • secondary to peroneal spasticity
  • Physical exam
    • inspection
      • hindfoot valgus
      • forefoot abduction
      • pes planus
    • range of motion
      • limited subtalar motion
      • heel cord contractures
      • arch of foot does not reconstitute upon toe-standing   
        • hindfoot remains in valgus (does not swing into varus) upon toe-standing
    • special tests
      • reverse Coleman block test
        • evaluate for subtalar rigidity
Imaging
  • Radiographs
    • recommended views
      • required
        • anteroposterior view
        • standing lateral foot view
        • 45-degree internal oblique view
          • most useful for calcaneonavicular coalition
        • Harris view of heel
    • findings
      • calcaneonavicular coalition  
        • "anteater" sign
          • elongated anterior process of calcaneus
      • talocalcaneal coalition
        • talar beaking on lateral radiograph
          • occurs as a result of limited motion of the subtalar joint
          • irregular middle facet joint on Harris axial view
        • c-sign  
          • c-shaped arc formed by the medial outline of the talar dome and posteroinferior aspect of the sustentaculum tali
        • dysmorphic sustentaculum
          • appears enlarged and rounded
  • CT scan 
    • Has been suggested as part of the preoperative workup to
      • rule-out additional coalitions
        • incidence approx. 5%
      • determine size, location and extent of coalition  
        • size of talocalcaneal coalition based on size of posterior facet using coronal slices  
  • MRI
    • may be helpful to visualize a fibrous or cartilaginous coalition
    • STIR sequences help to differentiate inflammatory changes (e.g. tendinitis) in local structures 
Treatment
  • Nonoperative
    • observation, shoe inserts
      • indications
        •  unclear. 
      • techniques
        • medial arch support and preserved hindfoot alignment
      • outcomes
        • In rigid flat feet shoe inserts may be the cause of discomfort.
    • immobilization with casting, analgesics
      • indications
        • initial treatment for symptomatic cases    
      • techniques
        • below-knee walking cast for six-weeks
      • outcomes
        • up to 30% of symptomatic patients will become pain-free with a short period of immobilization
  • Operative
    • coalition resection with interposition graft, +/- correction of associated foot deformity  
      • indications
        • persistent symptoms despite nonoperative management  
        • coalition involves <50% of joint surface area
      • techniques
        • open vs arthroscopic coalition resection
        • interposition material 
          • extensor digitorum brevis (calcaneonavicular coalition)
          • split flexor hallucis longus tendon (talocalcaneal coalition)
          • interposed fat graft
          • bone wax
        • correction of associated hindfoot, midfoot or forefoot deformities
          • calcaneal osteotomy for hindfoot valgus
          • calcaneal lengthening to create arch after resection
          • heel cord lengthening if intraoperative ankle dorsiflexion is not past neutral
      • outcomes 
        • 80-85% will experience pain relief
        • poor outcomes
          • coalition resection >50% size of joint surface area
          • uncorrected hindfoot valgus 
          • associated degenerative changes 
    • subtalar arthrodesis
      • indications
        • role has not been well established
        • consider if coalition involves >50 % of the joint surface of a talocalcaneal coalition
      • technique
        • open vs. arthroscopic 
        • consider an associated calcaneal osteotomy with severe hindfoot malalignment
    • triple arthrodesis (subtalar, calcaneocuboid, and talonavicular)
      • indications 
        • advanced coalitions that fail resection
        • diffuse associated degenerative changes affecting calcaneocuboid and talonavicular joints
      • technique
        • open vs. arthroscopic
Surgical Techniques
  • Calcaneonavicular coalition resection  
    • approach
      • lateral or sloppy lateral position
      • anterolateral approach over coalition
    • incision
      • oblique incision just distal to subtalar joint
      • between extensor tendons and peroneal tendons 
    • technique
      • protect branches of superficial peroneal and sural nerves
      • reflect fibrofatty tissues in sinus tarsi anterior and extensor digitorum brevis distally
      • identify coalition between anterior process of calcaneus and navicular bones and confirm with fluorscopy
      • excise bar with saw or osteotomes, which leaves defect ~1cm in size
      • interpose fat, bone wax or portion of extensor digitorum brevis muscle into defect
    • post-operative
      • short-leg, non-weight bearing cast for 3-4 weeks
  • Talocalcaneal coalition resection  
    • approach
      • positioned supine
      • medial approach to hindfoot
    • incision
      • horizontal or curved incision centered over sustentaculum tali
      • between flexor digitorum longus and neurovascular bundle
    • technique
      • sustentaculum tali usually just plantar to the talocalcaneal coalition
      • identify normal subtalar joint cartilage by dissecting out the anterior and posterior facets
        • this will help determine location and size of coalition resection
        • confirm with two needles immediately anterior and posterior to coalition clinically and confirm with fluorscopy
      • resect coalition with high speed-burr, ronguers and curettes
      • invert and evert subtalar joint to demonstrate improvement in subtalar motion
      • interpose fat, bone wax or portion of flexor hallucis longus tendon into defect
    • post-operative
      • short-leg non-weight bearing cast for three weeks
Complications
  • Incomplete resection
  • Recurrence of the coalition
  • Residual pain or stiffness 
    • due to malalignment or associated arthritis
    • due to unrecognized 2nd coalition - this should be identified by a preoperative CT scan

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