Cavovarus Foot in Pediatrics & Adults - Pediatrics

Introduction

Deformity characterized by
- cavus (elevated longitudinal arch)
- plantarflexion of the 1st ray and forefoot pronation
- hindfoot varus
- forefoot adduction
Epidemiology
- seen in both pediatric and adult populations
- 67% due to a neurologic condition
- when bilateral often hereditary or congenital
Pathophysiology
- neurologic
  - diagnosis of neurologic condition is critical to render appropriate treatment
  - unilateral - rule out tethered spinal cord or spinal cord tumor
  - bilateral - most commonly Charcot-Marie-Tooth (CMT) disease
  - muscle imbalances generate deformity
    - weak tibialis anterior and peroneus brevis overpowered by strong peroneus longus and posterior tibialis
    - results in plantarflexed 1st ray and forefoot pronation with compensatory hindfoot varus
      - with the 1st metatarsal plantflexed and forefoot pronated, the medial forefoot strikes ground first
      - the subtalar joint supinates to bring the lateral forefoot to the ground and maintain three-point contact, resulting in hindfoot varus
      - while initially flexible, hindfoot varus can become rigid with time
- idiopathic
  - usually subtle and bilateral
- traumatic
  - talus fracture malunion
  - compartment syndrome
  - crush injury
Associated conditions
- conditions which present with cavovarus foot
  - Charcot-Marie-Tooth disease
  - Cerebral palsy
  - Freidreich's ataxia
  - Spinal cord lesions
  - Polio
- conditions caused by the presense of cavovarus foot
  - see complications below
Prognosis
- depends on
  - deformity severity
  - etiology
  - patient age

Presentation

History
- recurrent ankle sprains and lateral ankle pain
  - peroneal tendon pathology
- lateral foot pain
  - excessive weight bearing by the lateral foot due to deformity
  - can result in 5th metatarsal stress fractures
- painful plantar calluses under 1st metatarsal head and 5th metatarsal head or base
- plantar fasciitis
  - elevated medial arch, forefoot pronation and tight gastronemius lead to contracture of the plantar fascia
Physical exam
- Coleman block test
  - evaluates flexibility of hindfoot deformity
  - technique
    - place 1" block under the lateral foot
    - eliminates contribution of the plantarflexed 1st ray and forefoot pronation to the hindfoot deformity
  - findings
    - flexible hindfoot will correct to neutral or valgus when block placed under lateral aspect of foot
    - rigid hindfoot will not correct to neutral
  - guides surgical treatment
    - flexible hindfoot deformities resolve with forefoot corrective procedures
    - rigid hindfoot deformities require corrective hindfoot osteotomy in addition to forefoot procedures
- peek-a-boo heel
  - anterior standing examination shows varus heel "peeking" around the ankle
- prominent first metatarsal fat pads
- Silfverskiold test
  - check dorsiflexion with both knee flexion and knee extension
    - if tight only with knee extension, then gastrocnemius is tight
    - if tight also with knee flexion, then soleus is also tight
  - gastronemius tightness often present with cavovarus foot
- altered gait
  - unstable base of support
  - increased double limb stance and decreased single limb stance
- wasting of 1st dorsal interosseous muscle of the hand
  - suggestive of CMT
- spine exam
  - scoliosis is suggestive of CMT
  - spinal dysraphism

Imaging

Radiographs
- recommended views
  - standing anteroposterior (AP), lateral radiographs of the ankle
  - standing AP, lateral and oblique radiographs of the foot
- findings
  - AP foot
    - talocalcaneal angle < 20° (nl 20-45°)
      - hindfoot varus
    - talonavicular overcoverage
      - talonavicular angle > 7° indicates forefoot adduction
    - metatarsal overlap
      - forefoot pronation
  - lateral foot
    - lateral talo-first metatarsal angle (Meary's angle) > 4° apex dorsal
      - break in Meary's line caused by plantarflexion of the 1st ray
    - calcaneal pitch or inclination angle > 30°
    - sinus tarsi see-through sign and double talar dome sign
      - due to external rotation of the ankle and hindfoot relative to the xray cassette, which is placed along the medial border of the adducted forefoot
    - bell-shaped cuboid
    - increased distance between base of 5th metatarsal and medial cuneiform
  - oblique foot
    - metatarsal stress fractures
    - calcaneonavicular coalitions

Studies

Electrodiagnostic Studies (EMG/NCS)
- diagnostic algorithm for CMT generally dictates
  - a neurologic physical exam
  - electrodiagnostic studies
  - genetic testing
Genetic studies
- used to confirm diagnosis after physical exam and electrodiagnostic studies

Treatment

Nonoperative
- accomodative shoe wear
  - indications
    - rarely sufficient except in mild deformity
- full-length semi-rigid insole orthotic with a depression for the first ray and a lateral wedge
  - indications
    - mild cavus foot deformity in adult (not indicated in children)
- supramalleolar orthosis (SMO)
  - indications
    - more severe cavovarus deformity recalcitrant to shoewear accomodations
- ankle foot orthosis (AFO)
  - indications
    - may be needed if equinus also present, resulting in equinocavovarus foot deformity
    - works best if equinus is a dynamic defomrity (not rigid)
- lace-up ankle brace and/or high-top shoe or boots
  - indications
    - may consider in moderate deformities when patient does not tolerate the more rigid bracing with an SMO or AFO
Operative
- soft tissue reconstruction
  - indications
    - failure of nonoperative treatment
  - performed with a combination of the following procedures
    - plantar release
      - indications
        
        cavus deformity
      - technique
        
        plantar fascia release
        
        Steindler stripping (release short flexors off the calcaneus)
    - peroneus longus to brevis transfer
      - indications
        
        plantar flexed first ray
      - technique
        
        decreases plantarflexion force on first ray without weakening eversion
    - posterior tibial tendon transfer
      - indications
        
        muscle imbalance
        
        posterior tibialis typically is markedly stronger than evertors and maintains strength for a long time in most cavovarus feet
        
        may consider transfer of posterior tibialis to dorsum of foot if severe dorsiflexion weakness of anterior tibialis
    - lengthening of gastrocnemius or tendoachilles (TAL)
      - indication
        
        true ankle equinus
        
        gastrocnemius recession produces less calf weakness and can be combined with plantar release simultaneously
        
        TAL should be staged several weeks after plantar release
    - 1st metatarsal dorsiflexion osteotomy
      - indications
        
        flexible hindfoot varus deformities (normal Coleman block test)
        
        corrects the forefoot pronation driving the hindfoot deformity
    - lateral ankle ligament reconstruction (e.g. Broström ligament reconstruction)
      - indications
        
        chronic ankle instability due to lignamentous incompetence following long-standing cavovarus
    - Jones transfer(s) of EHL to neck of 1st MT and lesser toe extensors to 2nd-5th MT necks
      - indication
        
        toe clawing combined with cavus foot
        
        performed if the indication is met and time permits
- lateralizing calcaneal valgus-producing osteotomy
  - indications
    - rigid hindfoot varus deformity (abnormal Coleman block test)
- triple arthrodesis
  - indication
    - almost never indicated due to very poor long-term results

Complications

Ankle instability
- standard lateral ankle ligament reconstruction will fail if cavovarus deformity is not concomitantly addressed
- untreated can lead to varus ankle arthritis
Stress fractures
- 5th metatarsal base (Jones fracture)
- 4th metatarsal
- navicular
- medial malleolus
Hallux sesamoiditis
- overload from plantarflexed 1st metatarsal head
Peroneal tendon pathology
- tendonitis, tears, subluxation or dislocation
- peroneus brevis most commonly involved
Plantar fasciitis
- contracture of the plantar fascia results from elevated medial arch, forefoot pronation and tight gastronemius