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Department
of Podiatry
Forefoot
varus and supinatus
Forefoot
varus
- a congenital,
fixed osseus deformity where the forefoot is inverted relative to
the rearfoot, when the subtalar joint (STJ) is in the neutral position
and the midtarsal joint (MTJ) is fully pronated / locked (see picture
above).
- theoretically due to inadequate valgus torsion of the head and neck
of the talus during foetal development, but this has not been well
supported
Incidence
- 8% of 116 female subjects (McPoil et al, 1988)
- 86% of 120 male and female subjects (Garbalosa et al, 1994)
Compensation
- compensation will occur via STJ pronation, to bring forefoot parallel
to the supporting surface
- forefoot inverted
- needs eversion to contact ground
- STJ compensates via pronation
3 patterns of compensation
· uncompensated
· fully compensated
· partially compensated
Uncompensated forefoot varus
- no pronation available at STJ to compensate
- forefoot held in inverted position
- excessive lateral contact throughout stance, with late stance phase
WB on IPJ of hallux
- can lead to HK over 5th MPJ and IPJ of hallux, excessive lateral
shoe wear
Fully compensated forefoot varus
- pronation at STJ to enable entire forefoot to contact ground
- excessive pronation unlocks distal structures
- STJ pronation increases MTJ ROM
- leads to forefoot hypermobility
- STJ pronates for longer period of stance - delayed resupination
- mechanically unstable
- unstable first ray
- associated with a wide range of pronation-induced mechanical foot
pathology
- propulsive instability
- PL required to plantarflex first ray during propulsion to stabilize
forefoot, however...
- STJ pronation changes angle of pull of PL, decreasing the lever
arm for plantarflexion, therefore...
- effect
of XS pronation on FDL function
-effect
of excess pronation on TA function
- when the medial plantar aspect of the foot contacts the ground,
the first ray is pushed into dorsiflexion, rendering the forefoot
unstable
Pathologies associated with XS STJ pronation
- shin splints
- plantar
fasciitis
- tibialis posterior tendonitis
- patello-femoral syndrome
- lesser digital deformity
- hallux abducto valgus
- lower back pain
- sciatica
- metatarsal stress fracture (see Hughes, 1983)
Partial compensation
- 'spectrum' of compensation
- wide range of available STJ pronation
- can be associated with HK under 4th MPJ, tailor's bunion
Summary
- fixed, osseus congenital deformity
- three patterns of compensation
- uncompensated
- fully compensated
- partially compensated
- associated with numerous pathologies
Forefoot
supinatus
- triplanar
acquired soft tissue contracture of the forefoot in an supinated position
around the longitudinal axis of the midtarsal joint
- caused by any pronatory force which drives the calcaneus past vertical,
which causes compensatory supination about the longitudinal axis of
the MTJ, such as large AoG, ankle equinus, external limb position,
etc.
- over time, the soft tissues will adapt to this position, holding
the forefoot in a supinated position (via Davis' Law)
Longitudinal axis supination
- LAMTJ is triplanar, but predominantly inversion / eversion
- LAMTJ does the opposite to the STJ
- STJ pronated - LAMTJ supinated
- LAMTJ supination occurs when Tib. Ant contracts or GRF's dorsiflex
medial column of the foot
Davis' law of soft tissue
- 'Ligaments and other soft tissues, when placed under unremitting
tension, elongate by the addition of new material. When remaining
uninterrupted in a lax state, they gradually shorten by the absorption
of material'
- peroneus longus is stretched and therefore elongates
- tibialis anterior is shortened and therefore contracts
Orthotic considerations
- forefoot supinatus should not be supported in an orthotic device
- prevents resolution of supinatus
- may restrict first MPJ dorsiflexion
- theoretically, a forefoot supinatus will resolve over time if rearfoot
pronation is controlled
- supinatus contracture may be partially or wholly reduced when taking
plaster impressions
- the aim of the orthosis is therefore to control the excessive rearfoot
motion which is causing the excessive LAMTJ supination
Summary
- reducible,
soft tissue contracture
- occurs secondary to XS pronation
- may coexist with a forefoot varus
- DDx is difficult
- assess MTJ ROM around long. axis
- if restricted - supinatus
- orthotic control should aim at controlling XS STJ pronation, not
supporting supinatus
 References
Garbalosa
JC, McClure MH, Catlin PA, Wooden M (1994) The frontal plane relationship
of the forefoot to rearfoot in an asymptomatic population. J Orthop
SPorts Phys Ther 20(4): 200-206.
Hughes LY (1985) Biomechanical analysis of the foot and ankle for
predisposition to developing stress fractures. J Orthop Sports Phys
Ther 7(3): 96-101.
Kidd R (1983) The pathomechanics of forefoot supinatus. The Chiropodist
39(7):255-261.
Lawley MG (1983) The pathomechanics of forefoot varus. The Chiropodist
38(11):416-421.
McPoil TG, Cameron JA, Adrian MJ (1987) Anatomical characteristics
of the talus in relation to forefoot deformities. J Am Podiatr
Med Assoc 77(2): 77-81.
Michaud TC (1993) Foot orthoses and other forms of conservative
foot care. Williams and Wilkins, Baltimore, p. 64-77.
Roy KJ, Sherer P (1987) Forefoot supinatus. J Am Podiatr Med Assoc
76(7): 390-394.
The diagram
at the top of the page was adapted from Michaud (1993)
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