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In Depth Tutorials and Information
Variation in tread line wear - rigid foot
A rigid foot may present for several reasons:
1.
Developmental abnormalities that result in a need for compensatory
supination of the foot, for example, rigid forefoot valgus.
2.
Neurological pes cavus.
3.
Iatrogenic rigidity following surgery.
4.
The pitch of the midtarsal joint axis is so high that a forefoot
supination contracture develops.
All these types will tend to produce excessive amounts of wear across
the tread line of the shoe. This is because there is a lack of toe function
owing to a combination of retraction and abducto-varus deformity. There
is often no toe to ground contact and the metatarsal heads have to bear
all the weight that would normally be assumed by the toes during propul-
sion. Additionally, a combination of excessively high metatarsal pitch and
rigidity of the forefoot increases the stress under the metatarsal heads
even further.
Under normal circumstances the treadline wear should be even across
the sole, indicating approximately even weight bearing across the five
metatarsal heads. In the rigid foot the exact position of the most severe
wear will depend on the underlying cause of the functional rigidity.
In the majority of cases of pes cavus produced by neurological disease
the wear across the tread will be over the first metatarsal head and the
fifth metatarsal head. A similar pattern will be seen in a patient with a leg
length difference on the supinating side. A subtle alteration will occur
when the rigidity of function is the result of a forefoot valgus deformity
that is compensating with subtalar joint supination. The residual midtarsal
joint supination will sufficiently unlock the forefoot to destabilize the first
ray and reduce its ability to bear weight. If the subtalar joint is functioning
in a fixed position throughout the midstance period, there may be signs
of an abductory twist under the fifth metatatarsal head, indicated by swirl
marks.
Variation in tread line wear - severe functionally
hypermobile pronated foot
With subtalar joint pronation, where the heel is everted and the midtarsal
joint longitudinal axis is supinated, there is often fully compensated
equinus. This results in similar wear patterns in the fore part of the shoe.
There will be subtle variations in the severity of the wear pattern depend-
ing on the exact cause of the instability. The later that excessive pronation
