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Department
of Podiatry
Preferred
Motion Pathway Theory of Foot Biomechanics & Foot Orthoses
Based on
concepts of Beno Nigg
Purposes
of foot orthoses:
1) Reduce injury
2) Realign skeleton
3) Improve cushioning
4) Improve sensory feedback
5) Improve comfort
Reduction of Injury
- Common reason
- evidence is that orthoses reduce injury
- no evidence as to which is best type of orthoses for which foot type
or injury
Aligning the skeleton
- effects are not systematic
- effects are subject specific
- are they an artifact of kinematic measurement
Impact cushioning/shock absorption
- Typically reduction is 10-20%
- is this clinically significant?
- Does it alter impact moderating behaviour?
- Does it produce adjustments in muscular response?
Improve sensory feedback
- Mechanoreceptors in sole of foot provide sensory input
- sensors detect input signals - at subject specific thresholds
- body responds mechanically by altering movement patterns
Improve comfort
- Comfort --> may be related to fit, less need for muscle stabilising
work, less fatigue, and damping of soft tissue vibrations
Based on these 5 concepts, Nigg proposes that the purpose of foot orthoses
are to
- minimise muscle work
- the body does this by following a preferred path for any given motion
(eg running)
- if it moves outside this path --> extra muscular effort --> injury
Basic steps of Nigg’s concepts
1) Based on the chosen movement, a force signal acts as an input variable
on the shoe
2) The shoe sole acts as a first filter for the force impact signal
3) The insert or orthotic acts as a second filter for the force input
signal
4) The plantar surface of the foot with its soft tissue and mechanoreceptors
acts as a third filter of the force input signal
5) The filtered information is transferred to the CNS that provides a
dynamic response based on subject specific conditions
6) The subject performs the movement for the task at hand
Therefore, the function of the orthoses is:
- The skeleton has a preferred path for any given movement task
- if an intervention supports the preferred movement path, muscle activity
is reduced. If an intervention counteracts the preferred movement path,
muscle activity must be increased
- an optimal orthoses reduces muscle activity
- an optimal orthotic feels comfortable because muscle activity and the
resulting fatigue are minimised
- since muscle activity is minimised, performance should increase with
an optimal orthoses
Muscle activity is minimised by
1) Stabilisation of joints
2) Minimising soft tissue vibration
Summary
- Subject specific responses
- orthoses should support the preferred pattern of motion
- Not clear yet how to measure:
- subject specific responses
- preferred pathways
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