Pes Cavus

INTRODUCTION

Definition

A defomity with an elevated longitudinal arch with calcaneus or varus hindfoot due to fixed plantar flexion of the forefoot, or, less frequently, as a result of excessive calcaneal dorsiflexion (calcaneus hindfoot).

Epidemiology

• Two-thirds of the patients with pes cavus have an underlying neurologic disorder, most commonly 
• Charcot-Marie-Tooth disease (CMT).
• The condition is seen in both pediatric and adult populations.
• Bilateral cases are often due hereditary or congenital causes.

Etiology

Overview: The exact etiology is unknown.
Neurologic conditions: Up to 67% of cases due to neurologic disorder. Conditions which present with cavovarus foot include:

• Charcot-Marie-Tooth disease (most commonly). Due to a defect in the gene responsible for peripheral myelin protein 22 (PMP22).
• Cerebral palsy.
• Polio.
• Freidreich’s ataxia.
• Myelomeningocele.
• Spinal cord lesions (injury, tumor, or abnormality).

Idiopathic causes: These are usually subtle and bilateral.
Traumatic condition:

• Talus fracture malunion.
• Compartment syndrome.
• Crush injury.

Patoanatomy

The primary structural problem is forefoot plantar flexion. 

• Muscle imbalance generate deformity:
  • Strong peroneus longus and posterior tibialis overpower tibialis anterior and peroneus brevis, resulting in plantarflexion of the first ray and forefoot pronation with compensatory hindfoot varus and a depressed first metatarsal head. First ray plantar flexion is more commonly caused by intrinsic weakness and contracture.
    • Tthe medial forefoot strikes the ground first with the first metatarsal plantarflexed and forefoot pronated.
    • For the lateral half of the foot to be in contact with the ground, the subtalar joint supinates to bring the lateral forefoot to the ground and maintain three-point contact, resulting in hindfoot varus.
    • Hindfoot varus can become rigid with time, while initially flexible, as the plantar fascia contracts.
  • Extensor hallucis longus activation will lead to dorsiflexion of the foot over time causing shortening of plantar fascia and resultant cavus.

CLINICAL FEATURES

Symptoms

• Patients may complain about ankle instability (ankle sprains).
  • Due to peroneal tendon pathology.
• Lateral foot pain: Caused by excessive weight bearing by the lateral foot due to deformity. May result in 5th metatarsal stress fracture.
• Painful plantar callus: Seen under first metatarsal head and 5th metatarsal head or base.
• Plantar fasciitis: Caused by contracture of the plantar fascia due to elevated medial arch, forefoot pronation and tight gastronemius.

Signs

General examination:

• Neurologic examination and a family history are essential. Consider genetics/neurology referral (DNA testing for CMT).
  • Unilateral involvement: Suggests a focal diagnosis (e.g. spinal cord anomaly, spinal cord tumor tethered spinal cord, or nerve injury).
  • Bilateral involvement: Common with Charcot-Marie-Tooth disease. Though, asymmetry may be seen in Charcot-Marie-Tooth disease.
• Spine exam: Scoliosis is suggestive of CMT.

Inspection:

• Gait: The patient will have an altered gait with unstable base of support and increased double limb stance and decreased single limb stance.
• Cavusvarus deformity is characterized by:
  • Cavus (elevated longitudinal arch).
  • Plantarflexion of the 1st ray and forefoot pronation.
  • Hindfoot varus.
  • Forefoot adduction.
• Prominent first metatarsal fat pads.
• Wasting of first dorsal interosseous muscle of the hand is suggestive of CMT.

Specific tests: 

• Silfverskiöld test: Check the dorsiflexion with both knee flexion and knee extension.
  • If there is tightness only with knee extension, then gastrocnemius is tight.
    • Gastronemius tightness often present with cavovarus foot.
  • If there is also tightness with knee flexion, then soleus is also tight.
• Coleman block test (lateral block test): Used to assess hindfoot flexibility of the cavovarus foot. Hindfoot flexibility is assessed by placing a 1-inch block under the lateral border of the foot. A flexible hindfoot corrects to neutral with a lift placed under the lateral aspect of the foot.

DIAGNOSIS

Conventional Radiography

Projections (views): Weight-bearing views are required. 

• Standing AP and lateral radiographs of the ankle.
• Standing AP, lateral and oblique radiographs of the foot.

Findings: 

• AP of the foot:
  • Talocalcaneal angle: < 20° (normal is 20-45°) suggests hindfoot varus.
  • Talonavicular overcoverage: The talonavicular angle > 7° indicates forefoot adduction.
  • Metatarsal overlap: Indicates forefoot pronation.
• Lateral of the foot:
  • Meary angle (lateral talo-first metatarsal angle): Increased, > 4° apex dorsal. The long axis of the talus will intersect the long axis of the first metatarsal dorsally on the lateral view of the foot. The normal value is 0° to 5°. The is a break in Meary line caused by plantarflexion of the first ray.
  • Calcaneal pitch (calcaneal inclination angle): Increased, > 30°, indicates a calcaneocavus foot. Intersection of a line running along the undersurface of the calcaneus and the floor. 
  • Sinus tarsi see-through sign and double talar dome sign: Occurs 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.
  • Other signs: 
    • The cuboid is bell-shaped.
    • There is an increased distance between base of 5th metatarsal and medial cuneiform.
• Oblique view of the foot:
  • Metatarsal stress fractures. 
  • Calcaneonavicular coalitions. 

Magnetic Resonance Imaging (MRI)

MRI of the spine (neuraxis) is indicated for unilateral cavus foot).

TREATMENT

Overview

• Use joint-sparing procedures whenever possible.
• Make the hindfoot flexible.

Treatment of Pes Cavus
Severity of Deformity	Examination	Treatment
Mild	Flexible, painless	Heel cord stretching, eversion/dorsiflexion strengthening program
Mild	Progressive or symptomatic	Plantar release ± peroneus longus to brevis transfer
	Varus because of peroneal weakness	Add tibialis anterior and/or posterior tendon transfer to the peroneal muscles
Moderate	Rigid medial cavus	Dorsiflexion osteotomy of either first metatarsal or cuneiform
	Rigid medial and lateral cavus	Dorsiflexion osteotomies of the cuboid and cuneiforms
	Rigid hindfoot varus	Closing/sliding calcaneal osteotomy
	Clawing of hallux	Add EHL transfer to first metatarsal (Jones)
Severe	Not correctable to plantigrade with other procedures	Triple arthrodesis is rarely needed and should be avoided whenever possible.

Nonoperative Treatment

Method: 

• Accomodative shoe wear is rarely sufficient except in mild deformity.
• Full-length semi-rigid insole orthotic with a depression for the first ray and a lateral wedge is indicated with mild cavus foot deformity in adult (not indicated in children).
• Supramalleolar orthosis (SMO) may be used in more severe cavovarus deformity recalcitrant to shoe wear accommodations.
• Ankle foot orthosis (AFO) may be needed if equinus also present, resulting in equinocavovarus foot deformity. It works best if equinus is a dynamic deformity (not rigid).
• Lace-up ankle brace and/or high-top shoe or boots may consider in moderate deformities when patient does not tolerate the more rigid bracing with an SMO or AFO.

Outcome: Nonoperative management rarely successful once deformity has developed.

Operative Treatment

Generally:

• Soft tissue procedures: Indication with failure of nonoperative treatment. Includes plantar fascia release and tendon transfer.
  • Percutaneous plantar fascia release is insufficient to correct a cavus foot. An open release and soft-tissue rebalancing are needed.
  • Achilles tendon lengthening should not be performed concomitantly with plantar fasciotomy.
  • An intact Achilles tendon provides the resistance necessary to stretch the contracted plantar tissues and correct the cavus deformity.
• Osteotomies: Calcaneal osteotomy can be used if the hindfoot is fixed in varus.
• Triple arthrodesis: Used for rigid deformity in skeletally mature patients.

Operation Methods

Soft tissue reconstruction:

• Plantar release: Indicated with cavus deformity.
  • Method: Plantar fascia release and Steindler stripping (release short flexors off the calcaneus).

COMPLICATIONS AND PROGNOSIS

Complications

Ankle instability: If untreated can lead to varus ankle arthritis. 

• Treat the cavovarus deformity concomitantly with the standard lateral ankle ligament reconstruction.

Stress fractures: Include fracture of the 5th metatarsal base (Jones fracture), 4th metatarsal, navicular bone, and medial malleolus. 
Hallux sesamoiditis: Due to overload from plantarflexed first metatarsal head.
Peroneal tendon pathology: Involves most often the peroneus brevis tendon. Includes tendonitis, tears, subluxation or dislocation.

Prognosis

The prognosis depends on deformity severity, etiology and patient age.