Forefoot Varus

Forefoot varus is a construct that is defined as foot type which is a congenital, fixed osseous deformity where the forefoot is inverted relative to the rearfoot, when the subtalar joint is in its defined neutral position and the midtarsal joint is fully pronated. It is often confused with forefoot supinatus. It was first described using this definition by Merton Root as part of the model that is commonly referred to as Root Theory.

Aetiology:
As part of the definition of the construct, forefoot varus is theoretically due to an inadequate valgus torsion of the head and neck of the talus during ontogenetic development. During normal fetal development the head and neck of the talus are initially plantarflexed and inverted; during development the head and neck derotates so that at birth the forefoot it is still slightly inverted relative to the rearfoot, but eventually it is assumed that by ages 5-6 that the forefoot should align with the rearfoot. Forefoot varus exists if something stops this normal development just short of what is assumed as being ideal. The reason for that halt in normal development is not known, but it could just be within the normal range of anatomical variation. If the head and neck of the talus rotate further beyond the position that results in a forefoot perpendicular to the rearfoot, then a forefoot valgus results. It is also possible that there may be an osseous abnormality in the talonavicular and/or calcaneocuboid joint(s).

A talipes equinovarus clubfoot is an extreme version of this where the head and neck of the talus remain in a plantarflexed and inverted position.

Prevalence:
Forefoot varus is rare. Studies have put its prevalence varying from 8% to 86%; but these studies did not distinguish between forefoot varus and supinatus and in some studies it is not clear if the midtarsal joint was placed in its defined ‘locked position’ which lead to an artificial higher prevalence. The prevalence is probably only a few percent of the population.

Assessment:
The determination as to if a forefoot varus is present is based on applying the definition of the construct above; ie the forefoot is inverted relative to the rearfoot when the subtalar joint is in its defined neutral position and the midtarsal joint is maximally pronated AND forefoot supinatus is ruled out. Typically the plantar plane of the forefoot is compared to a real or imagined bisection of the posterior aspect of the calcaneus using this technique. This foot type has a very low arch profile on both non-weightbearing and weightearing.

Pathomechanics:
The pathomechanics of this foot type is based on the foot needing to assume a plantargrade position when weightbearing, so compensation will occur via subtalar joint (STJ) pronation to bring the medial side of the forefoot to the ground. The exact pattern of compensation will depend on range of motion available at STJ.

1) Uncompensated Forefoot Varus:
• No pronation available at STJ (rigid subtalar joint)
• During gait the forefoot will remain in an inverted position
• Excessive lateral contact throughout stance phase
• Commonly get hyperkeratosis over 5th metatarsal head and IPJ of hallux

2) Fully compensated Forefoot Varus:
• Sufficient pronation is available at the STJ to bring medial side of the forefoot to ground
• This excessive pronation then “unlocks” distal structures (theory of proximal stability), leading to an unstable foot, potentially resulting in a range of pathologies or increasing the risk for them
• The calcaneus will be everted during weightbearing and the forefoot will be abducted
• STJ pronates for a longer period of time; the resupination that generally occurs later in the stance phase is delayed or does not occur.
• Commonly have a callus plantar to the second metatarsal head; fifth toe is often hammered; hallux abducto valgus is common.
• Unstable foot and excessive pronation increases the risk for the development of a wide range of pathologies

3) Partially compensated Forefoot Varus:
• Some motion is available at the subtalar joint
• Medial side of the forefoot will still be off the ground during stance, so foot tends to abduct during late midstance to compensate for that
• Function and pathologies are between the uncompensated and fully compensated types

A foot type has been described in which the lateral column of the foot is plantarflexed, in which the 4th and 5th metatarsal heads are plantar to the plane of the rearfoot. This technically does not meet the definition of a forefoot varus, but this foot type presumably functions the same as a forefoot varus.

Management:
A forefoot varus can not be corrected (see the definition), so needs to be compensated for. Generally the management is with a functional foot orthoses with posting on the medial side of forefoot to bring the ground up to the foot so that it does not have to pronate at the rearfoot to compensate.  For custom orthotics, the foot is typically modeled in the subtalar joint neutral and midtarsal joint locked position.

The foot orthotic should not be excessively posted medially under the forefoot so that normal plantarflexion of first ray can still occur during gait and the function of the windlass mechanism is not interfered with.

The forefoot posting for this can only be done on a rigid foot orthotic if it is to affect the rearfoot. Generally a foot orthotic that is less than rigid with a medial forefoot post in order to affect the rearfoot is going to have to dorsiflex the medial column of the forefoot to end range of motion and then invert the forefoot on the rearfoot at the midfoot joint to end range of motion before it can affect the rearfoot. Whereas, a medial forefoot post on a rigid orthotic shell will immediately affect the rearfoot via the tilting of the rigid 'plate'.

In athletes the use of the “anti-pronation” features in running shoes are likely to be ineffective in this foot type to prevent the abnormal compensatory pronation, as the medial side of the forefoot still needs to get to the ground. No amount of gait retraining or muscle strengthening will alter this foot type and compensations for it.

Commentary:

  • there is a lot of misunderstandings about this foot type and lot of misinformation is being written about it online, in journal articles and in books (Dunning–Kruger effect). A lot of this is based on the failure to stick to the definition above of what forefoot varus is, leading to confusion with it and forefoot supinatus and a failure to load the lateral column in clinical practice and research when determining if it is present.
  • most forefoot varus feet probably have some degree of forefoot supinatus as well
  • some clinicians think they see forefoot varus commonly, but are probably confusing it with a forefoot supinatus which is more common (table of differences and research on forefoot varus)
  • more inexperienced clinicians appear to see it more often than experienced clinicians. This may be because forefoot varus pathomechanics is easy to understand, whereas the pathomechanics of the opposite foot type, forefoot valgus is more difficult to understand. The compensation for both foot types can be subtalar joint pronation.
  • forefoot varus is sometimes stated as being a very 'destructive' foot type as the compensation as part of the pathomechanics moves the calcaneus past vertical (eg a rearfoot varus foot type does not go past vertical and is considered less 'destructive'). Pathomechanical entities that move the calcaneus past vertical are considered to have more pathology (ie 'destructive').
  • There is some controversy if this foot type actually exists or not; but this appears to be based on "research" done on forefoot varus, when the research was probably done on an inverted forefoot, which would have included a mix of feet with a true forefoot varus and forefoot supinatus.
  • In cycling communities, forefoot varus is seen as being very common and apparently, cleats need to be modified for that.

External Links:
Forefoot varus (Podiatry Arena)
The effect of forefoot varus on the hip and knee and the effect of the hip and knee on forefoot supinatus … (Running Research Junkie)

Related Topics:
Forefoot supinatus | Forefoot-rearfoot relationship | Forefoot Invertus / Inverted Forefoot | Forefoot Valgus | Dorsiflexed first ray / metatarsus primus elevatus | Forefoot Posting | Forefoot to Rearfoot Relationship

Page last updated: Sep 4, 2017 @ 11:54 am

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