Department of Podiatry

Sagittal Plane Facilitation of the Foot

Why a different model(s)?

Clinical practice is informed by theoretical interpretations of research and clinical observations

The traditional model (based on the two constructs of the neutral position of the subtalar joint and locked position of the midtarsal joint) is one theoretical interpretation

Science has shown a poor fit between this traditional model/theory and reality

The sagittal plane model is another attempt at a theoretical interpretation of research and clinical observations

Understanding different models

It is important that all models or theories are viewed and evaluated on their own terms and not in the terms of another model or 'mindset'

For example, left or right wing politicians will always evaluate policies in the terms of their own theory or mindset rather than evaluate the policy on its own terms

"The way a particular individual perceives and responds to what goes on in clinical practice is constructed within an individual paradigm constructed from prior experiences, interactions and interests. Individual practitioners can have faulty paradigms that do not allow them to develop and incorporate new knowledge into clinical practice. The trouble that many have in understanding new theories is not necessarily due to any difficulty of the new theory, but from the particular 'lens' or 'framework' of the existing theory that the new theory is viewed". Payne & Dananberg AJPM 31(1) 7-11 1997

What does this mean?

Back when Mert Root, John Weed and Bill Orien first proposed what is being referred to as the traditional theory many people rejected what they were saying as they where trying to interpret the theory within the framework of their current theory or model or mindset. As it did not fit, they rejected it.

In order to understand what Root et al were saying, an individual had to "set aside" their current understanding

Evaluate a theory in its own terms

This is what the "throw the baby with the bath water" metaphor refers to - evaluate theories on their own terms

We interpret the world around us through the 'lens' of our own mindset - for example a 'Marxist' will interpret the role of women in the work force different to a 'feminist'

Another example is the police detective who can easily develop a 'mindset' or theory about a crime and become unintentionally 'blinded' by this mindset when seeking clues to support his theory when he should be open to all possibilities

The skill in understanding different approaches and making clinical decisions is being explicit about the framework you are using

Principles it is based on:

the foot must be able to resist forces that are applied to it (this should be obvious)

this must co-ordinate with the power input which is required to move the body forward over the foot

the foot has its 3 autosupportive mechanisms

There needs to be a co-ordination between the foots autosupport and the creation of power for forward movement ie the autosupport must happen when the "power" goes on

Autosupport 1: Hicks (1954)

the windlass mechanism understand as a winch with the hallux as a handle dorsiflexion of the first metatarsophalangeal joint pulls on the plantar aponeurosis, shortening the distance between the first metatarsal head and calcaneus this supinates the foot and co-ordinated with external rotation from above. This mechanism requires first metatarsophalangeal joint dorsiflexion

Autosupport 2: Bösjen-Mollor (1979)

a close packing of the calcaneo-cuboid secondary to a timely tightening of the plantar aponeurosis compresses joint just prior to heel off require weight flow be directed in a timely manner at the first interspace (the high gear, low gear - vide infra) This mechanism requires first metatarsophalangeal joint motion

Autosupport 3: Locked Wedge Effect

compressive loading of the osseous structures

This will only occur if dorsiflexion occurs at the metatarsophalangeal joint motion for this to happen?

High gear & low gear (Bösjen-Moller, 1979)

two metatarsal head axes system

oblique axis - metatarsal heads 2 to 5 - has a shorter lever arm or radius to achilles tendon

transverse axis - metatarsal heads 1 to 2 - has a longer lever arm to achilles tendon

least resistance is provided by the shorter lever arm, i.e. the oblique axis - so this is used to begin unweighting the heel ---> weight flow to the lateral column

As heel unweighting progresses, must switch to the transverse axis for autosupport to be established ---> weight flow to the first web space

The perpendicular bisections of each axis show the longer radial arm from the heel to the transverse axis (Btr) versus the shorter radial arm to the oblique axis (Bobl). The greater the radial arm length, the greater the ability to develop greater thrust, hence high versus low gear push. Once the medial arm becomes engaged by weight shift to the transverse axis, it causes the 'closed packing' of the calcaneo-cuboid joint and secondary tarsal and midtarsal joint stability. (FBM, 1979)

A) - plantar fascial tightening during propulsion using transverse axis

B) -no transfer from oblique axis and no plantar fascia tightening

The auto support mechanisms are needed so the foot can resist stresses that are applied to it

They are dependent on sagittal plane motion at the first metatarsophalangeal joint

This co-ordinates with power input from above to facilitate forward movement of the body over the foot during single limb support

generally considered that at least 65° of dorsiflexion is needed at the first MPJ for normal function

this is dependant on first ray plantarflexion

a functional hallux limitus is present when there is a failure of the first metatarsophalangeal joint to dorsiflex during single limb support, regardless of its range on clinical examination

Functional Hallux Limitus (FHL) (a sagittal plane block)

if its present, even momentarily, it will result in a failure of the foots autosupportive mechanisms to be established

this occurs as the joint is a pivotal point for forward motion and at the time of greatest power input from above

this power has to be stored or dissipated

this is reflected as secondary motion at other sites

Compensation for a sagittal plane block: 1: Altered Heel Lift

the next most proximal joint to the first MPJ that allows motion in the sagittal plane is the MTJ

heel lift is delayed

visualised as late midstance pronation

Same Person

Full ROM during static double limb support
FHL during single limb support

Compensation for a sagittal plane block: 2: Vertical Toe Off

continuation of delayed heel lift heel lift is maximally delayed foot is just lifted of the ground apropulsive, laborious and slow gait Lack of heel off by time of contralateral heel contact

Compensation for a sagittal plane block: 3: Inverted Step

weight flow is directed to the lateral column and fails to shift medially to the first web space prior to heel lift happens when autosupport mechanisms are not established not to be confused with supination detectable on in-shoe plantar pressure measurements: also tends to cause wear on lateral aspects of shoes, despite excessive pronation of the foot this explains paradox of flexible forefoot valgus - ie a pronated foot with lateral forefoot shoe wear

Compensation for a sagittal plane block: 4: Abducted and adducted toe off

If FHL is present, the body will follow the path of least resistance to get around it

If the hip is in an externally rotated position ---> get around a FHL by directing weight flow medial to it ---> an abducted toe off

ditto for internally rotated hip

Compensation for a sagittal plane block: 5: Flexion Compensation of the Body

Generally need lateral slow motion video

flexion compensation at the middle of single limb support

failure of the knee to fully extend

lumbar spine will be straight (lumbar flexion) when it should be increasing its lordotic alignment in preparation for the impact loading of opposite limb contact

head flexion and TMJ dysfunction ?

Effect of a Sagittal plane block

Summary of Compensatory Motions

Joint	Normal motion (2nd half single support)	Compensation
Ankle	Plantarflexion	Dorsiflexion
Knee	Extension	Flexion
Hip	Extension	Flexion
Lumbar	Lordosis	Straightening (flat back)

The Diagnosis:

This is a diagnostic challenge as there are usually no symptoms at the first metatarsophalangeal joint.

The evaluation of the patient has to determine if the foots autosupportive mechanisms are being established

In shoe plantar pressure measurments and gait analysis are needed to if the compensatory mechanisms are taking place

Suspecting that it's present:

Without in-shoe plantar pressure measurements it is possible to suspect that it is present

observing the compensation during gait analysis - FROM THE LATERAL VIEW

lateral shoe wear

ROM of first MPJ tends to be restricted while the first ray is prevented from moving

the first metatarsal head tends to be wider

pain can sometimes be present on dorso lateral aspect of first MPJ

What to look for during a visual gait analysis:

the compensatory motions

especially the MTJ "collapsing" just as the heel comes off the ground

the late midstance phase pronation

the abductory or adductory twist

the delayed heel off

the flexed knee and hip

The orthotic management:

don't forget that this is just a part of the treatment plan

the orthoses must facilitate sagittal plane motion

the orthoses must allow the foot to establish the autosupportive mechanisms

the orthoses must facilitate appropriate weight flow through the foot, so weight initially is transfered lateral to initiate heel unweighting via the oblique axis then medially so the transverse axis is used ---> thrust for propulsion and to establish the autosupport

In a perfect world:

a test orthoses (prefab) will be used and evaluated by in-shoe plantar pressure measures and modified with the use of 'posts' to redirect the centre of pressure to what is assumed to be 'normal'

assesment and prescription is dynamic and objective - this will overcome some of the criticisms of the traditional model

the aim of the forefoot and rearfoot posts redirect weight flow in the right direction at the right time

invariably the post often bear no relationship to the posts that would have been prescribed under the traditional model

In a less than perfect world:

the orthoses must allow the first ray to plantarflex and facilitate appropriate weight flow and tranfer from the oblique to the transverse axis

This can be done by:

1) first ray cut outs

2) plaster additions

3) the Kinetic Wedge®:

4) the valgus and subproximal phalanx padding

these can be applied as temporary padding on a prefab before a cast is taken - the prescription can be based on the "test" orthoses

So why do our current orthoses work?

do they work because of brute force?

or do they work because of the inverted heel and plaster additions in the medial arch allow first ray plantarflexion ----> the foot's autosupportive mechanism become established and efficient transfer from oblique to transverse axis

is stopping the foot excessively pronating the goal or is the goal to let the foot establish its own autosupport mechanism?

Does this mean that our current orthoses work by accident or design? - ie the work despite the theory that underpins them rather than because of the theory

Some invalid criticisms directed at the sagittal plane model

A well documented defence mechanism to new theories/ideas is to claim that that they are not really new at all (the sagittal plane theory is new)

'knowledge disavowel' is another well documented concept - it is defined as a the avoidance of knowledge in order to preserve the status quo

Root et al - talked about functional hallux limitus in Vol 2 (they did, but that does not mean that the theoretical framework is not new)

the contralateral wedges are modifications to the outside of a shoe to "unscrew" a 'flatfoot' that were used pre-Root days. They consist of a medial heel wedge and a lateral forefoot wedge. The sagittal plane theory offers an explanation as to why/how these works, but because they explain how an old device works does not mean the theory is not new nor invalidate the theory

it's just theory! (...of course it is - that does not invalidate it)

the 'sagittal' name may be unfortunate as it does not imply that it focuses just on the sagittal plane. It focuses on the sagittal plane as much as the traditional model focuses on the frontal plane (...however critics latch on to the "sagittal" plane and then claim that they focus on all three body planes and not just the sagittal plane)

a number of critics claim that what they currently do works, so why bother:

- 'the rules of the game have changed' - we now have evidence based practice, so this kind of argument is no longer acceptable in today's environment

- why does what they do work? - the sagittal plane model provides a different explanation for the same thing

- where is the evidence?

* those who use this argument misunderstand the role of theory in informing clinical practice

* where is the current evidence for the traditional model - THERE IS NONE

* there is no evidence for eg the appropriate direction of weight flow through the foot - it is an assumption of the model. HOWEVER there is no evidence for the subtalar joint neutral position. BUT both are probably pretty good assumptions.

Some of the REAL problems with the sagittal plane model

It still needs more development - as an explanatory framework, its only been around for a short time

Can't explain everything and it does not attempt to (compare that history of dogma in the profession in which the traditional model was used to try and explain everything)

The difficulty of visualising a functional hallux limitus

The lack of clearer guidelines for clinical management

The need for computerised in-shoe plantar pressure measurements to properly apply the theory

No evidence for the assumed normal direction and timing of weight flow

What causes functional hallux limitus?

Payne & Dananberg (1997):

"A theoretical model is not necessarily right or wrong. It is valid insofar as its useful to inform clinical practice. They are offered as interpretations which can be validated by practical needs"

we use theories to interpret the world around us - the sagittal plane of facilitation model give us another model to interpret foot function

The final word

vanLeeuenhok when first trying to explain to an audience about the existence of micro-organisms was not believed. They believed him when they could use the microscope.

The moral of this story - "the non-believers are the technologically blind"

the non-believers of the sagittal plane models are technologically blind - I challenge them to use the in-shoe pressure measuring system and explain what they seeing in terms of the traditional model

Content Approved by: Head of Podiatry
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Last Updated: August 20th, 2002