Paradigm
‘A framework which includes the theoretical assumptions used to explain observations, and the practical method of applying these concepts’ (Payne, 1998)
Simply, a way of viewing events that occur in the world

Outline
History & paradigms in podiatric pathomechanics
Muscular ‘weak’ flat foot
Tripod model
Morton’s foot
Flexible/rigid high/low arch
Root model
Sagittal plane facilitation of the foot model
Concepts for podiatric pathomechanics

Quote...
Biomechanics:
‘a necessary basic science for the field of podiatry. No specialty in the field of medicine is more intimately involved, on an everyday basis, with the clinical application of biomechanics…’ (Merton Root, 1996)
‘the application of mechanical laws to living structures, as to a locomotor system’

The ‘flat’ foot
Also called a weak foot, pes valgus, pes planus, pes plano-valgus, ‘fallen arches’
Highly arched foot regarded as ideal - treatment involved ‘supports’ of metal or wood, shoe modifications and exercises to strengthen arch muscles
Originally described by Durlacher 1845 - built up leather inlay used to treat mechanical foot problems
Hugh Owen Thomas 1874 - ‘Thomas heel’ use of leather shoe sole additions Flat foot continued...
1888 - Royal Whitman was one of the first to describe in detail the pathomechanics of pes valgus
Believed muscle action is the primary mechanism of stability in the foot. ‘Weakfoot’ caused by ‘muscular defect’ leads to pain secondarily to ‘overwork’ of muscles and ligaments
Whitman Brace
Fabricated from sheet metal
High medial and lateral flanges
Designed to press on the navicular, causing the foot to invert from muscular contraction due to pain
Thought to increase muscle strength to raise the arch
1914 - P W Roberts developed a similar device with a deep heel cup and ‘varus heel wedge’ to supinate calcaneus
1927 - O F. Schuster combined the two devices to create the Whitman-Roberts plate

The ‘tripod’ model...
Prevalent in the 1920’s - 1930’s
Extension of the arch concept
Medial, lateral, transverse
Responsible for common orthopaedic view of ‘fallen’ transverse arch being responsible for ‘metatarsalgia’

Morton’s foot
1920’s - 1940’s: Dudley Morton describes the Morton’s foot and the Morton’s extension, and publishes ‘The Human Foot’
‘Arch strain’ due to ‘hypermobility’ of the first metatarsal
Treatment involved medial wedging of the shoe and the ‘Morton’s extension’.

Abnormal morphology
1948: Schrieber and Weinerman propose that alignment of forefoot to rearfoot is important, and that inverted and everted forefoot positions are abnormal and require ‘balancing’.
1950: Ben Levy’s ‘rubber butter’ to balance forefoot (the basis became the functional foot orthosis)
1949: Hiss’ Functional Foot Disorders describes a rational foot classification system Arch height/flexibility

Discovery of joint axes
Axes of the STJ, MTJ, 1st and 5th rays described (Manter 1941, Hicks, 1953)
Concept of midtarsal joint ‘locking’ and how this ‘locking’ was influenced by subtalar joint motion (Elftman, 1960)

Discovery of joint motion during gait
1956: Wright et al describe the motion of the rearfoot during gait

Root paradigm
Root model evolved from 1954-1966, providing a podiatric theory of biomechanics to guide therapy
Emphasized the foot as a dynamic rather than static structure
Drew together & developed:
Hick’s axial orientations (approximations of joint axes)
Wright et al’s rearfoot motion
Elftman’s locking of the MTJ
Schrieber & Weinerman and Levy’s ‘balancing’ of forefoot deformities

Basis was to classify normal & abnormal foot types (osseous alignment)
“Normal”/ideal foot alignment occurs when:
- distal 1/3 of leg vertical
- calcaneus vertical to supporting surface
- plantar forefoot parallel to plantar rearfoot

when in NCSP (also occurs during midstance period?)
Variations from this “normal’ foot alignment (‘intrinsic foot deformities’) lead to abnormal foot function

Protocol for treating
determine and measure intrinsic foot deformity
cast the foot to capture the deformity in a plaster model
construct a “functional foot orthosis” (wedges/posts)


A paradigm in conflict?
Single axis models
Criteria for normal foot alignment
McPoil et al (1988) - Only 17% of subjects had ‘normal’ foot alignment
Reliability of measurement procedures
Questionable interrater reliability for measuring deformities
Causation versus correlation
The chicken and the egg versus a viewed connection between two events
Lack of controlled trials on the effects of functional foot orthoses

Recent paradigms in podiatric pathomechanics
Sagittal plane facilitation of the foot (Payne, 1997)
Root model - views foot function primarily in the frontal plane (eg, normal foot protocol)

Sagittal plane model emphasizes sagittal plane motion of foot
- Foot is considered to have three ‘autosupportive’ mechanisms
- close-packing of calcaneocuboid joint
- windlass mechanism
- wedge-and-truss effect
- All require timely and efficient function of the foot in the sagittal plane (primarily 1st MPJ dorsiflexion) so that it can resist stress
- Blockage of this sagittal plane motion (even temporarily) leads to failure of 1+ mechanisms‡ foot unable to resist stress

Windlass mechanism
Plantar aponeurosis attached from medial calcaneal tubercle to proximal phalanges (ax 1st MPJ)
Dorsiflexion (65°) of the first MPJ pulls on plantar aponeurosis shortening distance b/w 1st MPJ & calcaneus thereby supinating the foot and enabling it to resist stress

Concepts for podiatric pathomechanics
Normal and abnormal motion
Neutral position of a joint
versus normal alignment
Normal and abnormal compensation
Hypermobility, versus large ROM, versus ligamentous laxity

Normal and abnormal motion
Motion may be considered ‘abnormal’ when it occurs
at an inappropriate time
to an excessive/inadequate degree
for an irregular duration of the gait cycle

Examples
Subtalar joint - abnormal pronation / supination
1st metatarsophalangeal joint (MPJ)
Subtalar joint
Abnormal pronation leads to ff hypermobility
when foot should be supinating (ie, after ffl)
beyond 6°

Abnormal supination leads to reduced shock attenuation
before FFL

‘Neutral’ position of a joint (Root et al.)
A reference position of a joint
?most stable position
Ankle joint (AJ)
foot 90° to leg
Subtalar joint (STJ)
neither pronated nor supinated
most mechanically efficient position
Midtarsal joint (MTJ)
fully pronated/locked position (about long & oblique axes)

Neutral position of foot = AJ, STJ, MTJ neutral
These joint positions are approximated simultaneously during midstance period of gait cycle (of an ideally functioning foot)
Reference position for casting for orthoses

‘Normal’ versus ‘Neutral’
Entirely different concepts from a podiatric perspective

‘Normal’ = ideal structure (ie, vertical lower leg, vertical calcaneus, parallel ff to rf)
‘Neutral’ = ideal alignment/functional position


Root model: ‘Normal’ foot type leads to ‘neutral’ position during midstance, ‘abnormal’ structure leads to ‘abnormal’ function
A structurally abnormal foot still has an ideal functional (neutral) position
Orthoses attempt to place the foot in an ideal functional alignment (neutral) - not ‘correct’ the ‘deformity’
(analogy - contact lenses)

Compensation (Root et al.)
‘A change of structure, position, or function of one part in an attempt by the body to adjust to a deviation of structure, position or function of another’

Normal
for locomotion, maintain balance
adapting to irregular terrain
increase surface area of the foot on ground
not repetitive, therefore not harmful

Abnormal
change in function as a result of structural abnormality
attempt to optimise function
repetitive and destructive
leads to pathomechanical function (eg, STJ triplanar)


Hypermobility, large ROM, or ligamentous laxity?
Terms are often confusing to students when confronted with joints having large ROM
hypermobility
large ROM
ligamentous laxity

Hypermobility
Movement of a segment or part which should be fixed and stable when stress is applied
Example: 1st ray hypermobility
‘A state of 1st ray instability that occurs while the forefoot is bearing weight’ (during midstance & propulsion periods)
Normal: STJ supination decreases MTJ ROM and stabilises 1st ray
Abnormal: STJ pronation increases MTJ ROM causing 1st ray motion (d/flexion)

Large range of motion (ROM)
May be characteristic of an individual joint (as opposed to a generalized condition affecting multiple joints such as ligamentous laxity)

Ligamentous laxity
Generalized condition often referred to as “double-jointedness”
Characteristic of specific connective tissue & CNS disorders
May occur in the absence of disease, particularly the young
Modified Carter & Wilkinson test (Beighton et al. 1973)
Modified Carter & Wilkinson test (Beighton et al. 1973)
1 point for each manouvre
Max. score = 9
Varying degress of hypermobility
Hypermobility
Score >4-5/9

Summary
Appreciation of history & paradigms in podiatric pathomechanics
Root paradigm : “Normal”/ideal foot alignement
Neutral joint (ankle, STJ, MTJ) positions
Compensation - normal versus abnormal
Hypermobility vs large ROM vs ligamentous laxity