Cavovarus Foot - Coleman Block Test and Staged Management
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
What is the Coleman block test and what does it tell you about this patient's deformity?
Explain the pathophysiology of cavovarus deformity in Charcot-Marie-Tooth disease.
What is your surgical management plan for this patient with bilateral flexible cavovarus feet?
How would your management differ if the Coleman block test showed a RIGID hindfoot?
What is the Jones procedure and when is it indicated?
What is the long-term prognosis and follow-up plan for this patient with CMT?
Key Teaching Points
| Concept | Detail |
|---|---|
| Coleman Block Test | Gold standard for assessing hindfoot flexibility; determines surgical strategy |
| Pathomechanics | PL > Tib Ant = cavus; Tib Post > PB = varus |
| Flexible vs Rigid | Flexible = forefoot surgery; Rigid = add hindfoot osteotomy |
| First Ray | Dorsiflexion osteotomy KEY procedure for flexible cavovarus |
| Tendon Transfers | PL to PB removes deforming force; Jones for claw hallux |
| Avoid Fusion | Preserve motion in young patients; triple arthrodesis is LAST resort |
Common Examiner Follow-up Questions
-
"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
-
"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
-
"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