Cavus Foot

Cavus Foot: Definition & Anatomy - High Arches, Hidden Issues

• Definition: Complex foot deformity with an abnormally high medial longitudinal arch; can be flexible or rigid.
• **Key Anatomical Features (Triplanar Deformity):
  • Hindfoot: Varus (most common), ↑ calcaneal pitch angle.
  • Midfoot: Adduction, plantarflexion of first ray (creates cavus).
  • Forefoot: Adduction, pronation (compensatory), claw toes (MTPJ extension, IPJ flexion).
• Terminology: Pes cavus, talipes cavus, high-arched foot.

⭐ The Coleman block test is essential to differentiate between forefoot-driven and hindfoot-driven cavus, guiding treatment decisions by assessing hindfoot flexibility when the first metatarsal is allowed to drop off the edge of a block.

Cavus Foot: Etiology & Pathomechanics - Why the Arch?

• Etiology (Often Neuromuscular):
  • Neurological (Most Common):
    • Charcot-Marie-Tooth (CMT) (📌 Cavus Mostly Together)
    • Friedreich's Ataxia, Spinal Dysraphism, Polio
  • Other: Trauma (e.g., compartment syndrome, malunion), Congenital, Idiopathic
• Pathomechanics (Muscle Imbalance):
  • Forefoot Driven: Peroneus Longus (PL) overpowers Tibialis Anterior (TA) → 1st ray plantarflexion.
  • Hindfoot Driven: Tibialis Posterior (TP) overpowers Peroneus Brevis (PB) → Hindfoot varus.
  • Intrinsic Imbalance: → Claw toes.
  • Result: ↑ Arch, rigid foot, ↓ shock absorption.

  ⭐ The Coleman block test helps differentiate flexible hindfoot varus (corrects with block) from rigid hindfoot varus in cavus foot, guiding surgical planning by assessing forefoot-driven deformity contribution to hindfoot varus.

Cavus Foot: Clinical Assessment - Spotting the Signs

• History: Onset (congenital/acquired), progression, pain (location, character), instability, family history (e.g., Charcot-Marie-Tooth disease), footwear issues.
• Observation:
  • High arch (medial longitudinal).
  • Hindfoot: Varus ("peek-a-boo" sign), increased calcaneal pitch.
  • Forefoot: Adduction, pronation, plantarflexed 1st ray.
  • Toes: Clawing. Callosities (lateral border, metatarsal heads).
• Gait: Lateral weight-bearing, ankle instability.
• Key Tests:
  • Coleman Block Test: Assesses hindfoot flexibility.
  • Thorough neurological examination (essential for etiology).

⭐ The Coleman block test is crucial: it differentiates a flexible hindfoot (corrects with block under lateral forefoot) from a rigid deformity, guiding surgical strategy.

Cavus Foot: Imaging & Classification - X-Ray Vision

• X-Rays (Weight-Bearing):
  • Lateral View:
    • ↑ Meary's Angle: >4° (Talus-1st MT) - apex dorsal.
    • ↑ Hibb's Angle: >45° (Calcaneus-1st MT).
    • ↑ Calcaneal Pitch: >30°.
  • AP View:
    • ↓ Kite's Angle (Talocalcaneal): <20° (hindfoot varus).
• Coleman Block Test: Differentiates flexible forefoot-driven hindfoot varus.
• Classification: Based on radiographic angles (severity) & deformity apex.

  ⭐ Meary's angle (talus-1st metatarsal) is key for identifying apex and severity of cavus deformity on lateral X-ray.

Cavus Foot: Management Principles - Fixing the Foot

• Conservative: Stretching exercises, custom orthotics (e.g., UCBL, lateral wedge for forefoot/hindfoot), appropriate footwear modifications.
• Surgical Goals: Relieve pain, improve stability, correct deformity.
  • Flexible Deformity: Plantar fascia release, tendon transfers (e.g., Peroneus Longus to Brevis, Hibbs).
  • Rigid Deformity: Bony procedures.
    • Osteotomies: Calcaneal (Dwyer), metatarsal (dorsiflexion).
    • Arthrodesis: For severe, arthritic joints (e.g., triple arthrodesis).
  • Apex of deformity guides surgical choice.

⭐ The Coleman block test helps differentiate forefoot-driven cavus (plantarflexed first ray) from hindfoot-driven cavus, guiding surgical strategy.

High‑Yield Points - ⚡ Biggest Takeaways

• Cavus foot: high-arched foot, often from neuromuscular disorders (e.g., Charcot-Marie-Tooth).
• Symptoms: painful callosities (metatarsal heads), claw toes, ankle instability, hindfoot varus.
• Coleman block test: crucial for assessing hindfoot flexibility and differentiating forefoot vs. hindfoot driven deformity.
• Radiographs: ↑ calcaneal pitch, ↑ Meary's angle, abnormal Hibb's angle.
• Treatment: orthotics initially; surgery (osteotomies, tendon transfers) for severe cases.
• Investigate for neurological causes (e.g., spinal dysraphism), especially if unilateral.