Forefoot Valgus

Definition:
A congenital, fixed osseous deformity where the forefoot is everted relative to the rearfoot, when the subtalar joint is in its defined neutral position and the midtarsal joint is in its assumed locked position.

Aetiology:
Theoretically due to an excessive valgus torsion of the head and neck of the talus during foetal development – not necessarily well supported. Could be due to deviations at the calcaneocuboid joint.

Prevalence:
Unknown – but could be up to 50% of all forefoot alignment problems. Widely considered to be ore common than forefoot varus. Garbalosa et al (1994) reported a prevalence of 9% and McPoil et al (1988) reported a prevalence of 45%.

Diagnosis:
See definition.

Pathomechanics of everted forefoot

The way a foot compensates for an everted forefoot is widely assumed to be dependent on the range of motion available at the MTJ and STJ’s.

Flexible everted forefoot:
• During gait the medial side of the forefoot will contact the ground prematurely
• There is sufficient range of motion at the MTJ to allow the lateral forefoot to reach the ground
• Traditional understanding is that this hypothetically ‘unlocks’ the midtarsal joint, so excessive pronation of this joint occurs, with forefoot hypermobility and the associated increased risk for pathology related to excessive pronation
• An alternative explanation is that the dorsiflexed first metatarsal as part of the compensation restricted first MPJ dorsiflexion and the foot autosupports from getting established (see sagittal plane blocks)
• There will be a high arch non-weightbearing (due to plantarflexed position of the first ray) but a lowered arch on weight bearing
• Tend to have lateral forefoot callus or a callus sub the 2nd metatarsal head; the forefoot tends to splay on weightbearing
• Position of calcaneus is usually everted from its neutral position due to STJ pronation from the “unlocked” MTJ – HOWEVER, the actual position of calcaneus may depend upon any rearfoot deformity (this will also apply to other foot types, as they do not necessarily appear in isolation).

Rigid everted forefoot:
• During gait the medial side of the forefoot will contact the ground prematurely and as there is insufficient ROM at the MTJ for the lateral forefoot to reach the ground, compensation occurs by STJ supination.
• These feet are rigid, poor shock absorbers and are at increased risk for ankle sprains
• There will be a high arch on both non-weightbearing and weightbearing
• Tend to have a callus plantar to the first and fifth metatarsal heads
• This is the typical ‘pes cavus’ foot

An alternative explanation for the pathomechanics of an everted forefoot and if it pronates or supinates at the subtalar joint is the relationship of the first metatarsal head relative to the subtalar joint axis. If the first metatarsal head is medial to the joint axis, a supinatory moment will be applied to the subtalar joint. If the metatarsal head is lateral to the subtalar joint axis  pronatory moment. The amount of pronatory or supinatory moment at the subtalar joint axis is likely to be also related to the ranges of motion at the tarsal joints (not necessarily the midtarsal joint).

Orthotic management of everted forefoot

Flexible:
Functional foot orthoses with rearfoot post and lateral forefoot post – for a true valgus this will be a ‘wedge’ and for a plantarflexed first ray, it will be a 2-5 ‘bar’
May need to compromise – lateral forefoot posting above 10 – 15 degrees may not fit in the shoe.

Rigid:
Orthoses with lateral forefoot post
Shock absorption.

 
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