Cavovarus Foot - Coleman Block Test and Staged Management

Clinical Scenario

A 14-year-old boy presents with bilateral foot deformity that has been progressively worsening over the past 3 years. He reports difficulty with walking, frequent ankle sprains, and calluses under his metatarsal heads. His mother has similar foot problems and was recently diagnosed with Charcot-Marie-Tooth disease.

History:

• Progressive bilateral foot deformity since age 11
• Recurrent lateral ankle sprains (4-5 per year)
• Difficulty finding shoes that fit
• Calluses under 1st and 5th metatarsal heads
• Mild fatigue with prolonged walking
• No significant back pain
• Family history: Mother with CMT Type 1A

Examination Findings:

• Bilateral cavovarus foot deformity
• High arch with plantarflexed first ray
• Hindfoot varus (visible "peek-a-boo" heel sign when viewed from front)
• Claw toes with extension at MTP joints, flexion at IPJs
• Wasting of EDB and intrinsic muscles
• Calluses under 1st and 5th MTH bilaterally
• Decreased ankle dorsiflexion (10° with knee flexed)
• Weak ankle evertors (MRC Grade 3+/5)
• Weak tibialis anterior (MRC Grade 4-/5)
• Positive Silfverskiöld test (tight gastrocnemius)
• Absent ankle jerks bilaterally
• Slightly decreased vibration sense distally

Coleman Block Test:

• When standing with lateral border of foot on a 2.5cm block (first ray hanging free)
• Right foot: Hindfoot corrects from varus to neutral → FLEXIBLE
• Left foot: Hindfoot corrects from varus to neutral → FLEXIBLE

Investigations

Imaging

Weight-Bearing Foot X-rays (AP and Lateral):

• Increased calcaneal pitch angle (35°, normal <30°)
• Increased Meary's angle (apex dorsal) indicating midfoot apex
• Plantarflexed first metatarsal
• Claw toe deformities visible
• No degenerative changes

Ankle X-rays:

• Normal mortise alignment
• No lateral ankle instability changes

Spine MRI (if indicated):

• Normal spinal cord, no tethered cord or syrinx

Special Investigations

Nerve Conduction Studies/EMG:

• Reduced motor and sensory conduction velocities
• Demyelinating pattern consistent with CMT Type 1

Genetic Testing:

• PMP22 gene duplication (CMT1A) - most common cause

Questions & Model Answers

Key Teaching Points

Common Examiner Follow-up Questions

1. "What other conditions cause cavovarus foot?"

   • Spinal dysraphism (tethered cord, syrinx)
   • Poliomyelitis
   • Cerebral palsy (hemiplegic)
   • Friedreich's ataxia
   • Idiopathic (club foot residual)
   • Compartment syndrome sequelae

2. "How do you counsel this family about CMT?"

   • Autosomal dominant inheritance (CMT1A)
   • 50% chance of passing to offspring
   • Variable expression even within family
   • Genetic testing available
   • Progressive but life expectancy normal

3. "What is the Hibbs procedure?"

   • Transfer of EHL and EDL through interosseous membrane to lateral foot
   • Augments dorsiflexion and eversion
   • Historical procedure, less commonly performed now

Related Topics

• Charcot-Marie-Tooth Disease
• Claw Toe Deformities
• Lateral Ankle Instability
• Tendon Transfers - Lower Limb
• Paediatric Foot Deformities