Rearfoot Varus

Rearfoot varus

Definition:
A fixed osseous deformity in which the posterior bisection of the calcaneus is inverted relative to vertical when the subtalar joint is in its defined neutral position.

Prevalence:
Very common. Greater then 4 degrees in 98% of the population in one study  maybe just a normal variant

Aetiology:
Assumed to be due to a failure of the calcaneus and tibia to fully derotate from their foetal varus positions.
3 causes:
1) Tibial varum (tibial influence) – distal third of tibia is in varus – due to failure of tibia to correct from infantile position; genu varum of Blount’s disease
2) Varus angulation of subtalar joint
3) Varus position of calcaneus – retention of foetal position

Rearfoot varus is the sum total of all three of the above
A varus position of the rearfoot complex may also be due to trauma.

A varus position of the calcaneus is considered normal up to ages 7 – 8 years.

Pathomechanics:
All 3 causes place the foot in an inverted position when the STJ is in its defined neutral position  the subtalar joint must pronate to bring the medial side of the foot to the ground. The compensation for a rearfoot varus will depend on the degree of the deviation and the amount of motion available at the STJ:

1) Uncompensated:
• No ROM at STJ – foot can not pronate to get medial side of foot to ground. Rare
• Foot strikes ground laterally and remains inverted.
• Poor shock absorber  pathologies associated with poor shock absorption.
• lateral ankle sprains common
• Lateral shoe wear; hyperkeratosis under 5th MPJ (usually severe)

2) Fully compensated:
• Adequate ROM of STJ to bring medial side of foot to the ground
• Common.
• Contact period pronation of foot is assumed to be more rapid and prolonged with delayed resupination
• Haglund’s deformity/retrocalcaneal bursitis is common
• callus formation plantar to metatarsal head 2 to 4 is assumed to be more common in those with rearfoot varus – due to dorsiflexion mobility of the first ray from the excessive subtalar joint pronation
• Arch height will be medium during weightbearing and non-weightbearing
• Increased risk for tissue damage associated with excessive pronation
• Not considered to be a very ‘destructive’ foot type with symptoms tending to be milder
• During stance the calcaneus will appear vertical and gait will not necessarily appear ‘abnormal’ – there will be no ‘Helbings’ sign (medial bowing of the achilles tendon)

3) Partially compensated:
• Some motion is available at STJ, but no sufficient for full compensation
• Patients walk with foot inverted to the ground, then abduct during propulsion
• Pathomechanics and clinical features are between the fully and uncompensated types

Clinical management:
Orthoses with medial wedging/posting to bring ground up to foot to prevent need for compensatory pronation.

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