3. FUNCTIONS OF ANKLE & FOOT
Stability
Provide stable base of support in variety of weight bearing
postures
Acts as a rigid lever for effective push off during gait
Mobility
Absorbs stress & shock – pliability of foot
Propulsion of body in walking
Protection – sensation of sole of foot
9. Muscle activity is critical for dynamic stability &
integration of movements at multiple joints of foot.
No muscle is single joint muscle.
Muscle function depends on –
Muscle structure &
Position of muscle in relation to joint axis
Anterior compartment muscles – Dorsiflexion
Posterior compartment muscles – Plantarflexion
Lateral compartment muscles – Pronation
Medial compartment muscles - Supination
12. Posterior compartment muscles
Passes posterior to the ankle joint & so all are
plantarflexors.
The muscles are –
Gastrocnemius
Soleus
Tibialis posterior
Flexor digitorum longus (FDL)
Flexor hallucis longus (FHL)
Peroneus longus
Peroneus brevis
Plantaris
13. Triceps surae
Two heads of gastrocnemius & soleus together
Strongest plantarflexor
Inserts perpendicular on the calcaneum – provides
large moment arm to provide plantarflexion torque.
Passes medial to the subtalar joint axis – supination
During weight bearing, helps lock the foot into a
rigid lever
Eccentrically control dorsiflexion in weight bearing
14. Tibialis posterior –
Important dynamic contributor to the arch support.
Controls & reverse foot pronation during gait cycle.
FHL & FDL –
Spans the medial longitudinal arch & supports arch during gait
cycle.
Also causes subtalar joint supination & flexion of toes.
FHL causes flexion of IP joints.
15. Lateral compartment muscles
Muscles are –
Peroneus longus
Peroneus brevis
Primary pronators of subtalar joint.
16. Anterior compartment muscles
The muscles are –
Tibialis anterior
Extensor hallucis longus (EHL)
Extensor digitorum longus (EDL)
Peroneus tertius
Strong ankle dorsiflexors.
Tibialis anterior – strong supinator of subtalar joint.
EHL – extension of MTP joint of hallux
EDL & peroneus tertius – pronation
EDL – extension of MTP joint of lesser toes
17. Intrinsic musculature
Important functions –
Stabilizes toes
Dynamic spport to the arches during gait
Muscles are –
Lumbricals
Dorsal & plantar interossei muscles
19. Also called as talocrural joint.
Synovial hinge joint Medial Lateral
20. STRUCTURE
Proximal articular surface –
Concave surface of distal tibia & of tibial & fibular malleoli.
Extends more distally on lateral than medial & on posterior
than anterior. (Mortise)
Proximal tibiofibular joint –
Plane synovial joint
Distal tibiofibular joint –
Syndesmosis or fibrous union
21. Distal articular surface –
Body of talus – 3 articular
surfaces
Large lateral fibular facet
Smaller medial tibial facet
Trochlear (superior facet)
Body – wider anteriorly
than posteriorly (Wedge
shape)
Cuboid
Head of
calcaneus
Fibular/lateral
facet
Navicular
Head of Talus
Body of Talus
Tibial facet
22. CAPSULES & LIGAMENTS
Capsule – thin & weak anteriorly & posteriorly.
So stability depends on intact ligaments.
Ligaments of proximal & distal tibio-fibular joints –
For stability of mortise & therefore ankle.
Crural tibiofibular interosseus ligament
Anterior & posterior tibiofibular ligaments
Tibiofibular interosseus membrane
Other ligaments -
Medial collateral ligament [MCL]
Lateral collateral ligament [LCL]
Extensor & peroneal retinaculae
Key support to subtalar
joint also
23. MCL –
Called as Deltoid ligament
Fan shaped
Superficial & deep fibers from borders of tibial malleolus to
navicular, talus & calcaneus.
Extremely strong ligament
Controls medial distraction forces on ankle
Checks motions at extremes of joint range
24. LCL –
3 separate bands referred as separate ligaments-
Anterior talofibular ligament
Posterior talofibular ligament
Calcaneofibular ligament
LCL components are weaker & more susceptible to injury than
MCL
Control varus (lateral distraction) forces
27. AXIS
Through fibular malleolus, body of talus & just below
or through tibial malleolus.
Tibial torsion – more posterior position of fibular
malleolus, due to normal torsion or twist in distal
tibia in relation to proximal tibia.
28. FUNCTION
Dependant on stability of tibiofibular mortise & for
mobility role mortise belongs primarily to fibula.
Shape of talus facilitate ankle stability.
Trochlea – wedge shape – in weight bearing, during
dorsiflexion tibia rotates over talus, wider anterior part
wedges into mortise to enhance stability.
This allows ankle to withstand compression forces of
450% of body weight.
This joint motion is necessary for –
Normal load distribution
Cartilage nutrition
Lubrication of ankle joint
29. Cont…
Plantarflexion – loosepacked position of ankle – less
stable – higher incidence of ankle sprain.
Asymmetry in size & orientation of lateral & medial
facets of talus – changes ankle mortise during
dorsiflexion – causes greater displacement of fibula
over lateral malleolus during dorsiflexion.
32. STRUCTURE
3 separate plane
articulations between
talus superiorly &
calcaneus inferiorly.
Triplanar movement
around a single joint
axis.
Variable articulating
surfaces, posterior being
consistent & largest.
Posterior facet receives
75% of stress of subtalar
joint.
33. Between posterior articulation & anterior & medial
articulation, forms a bony tunnel – tarsal canal.
Runs obliquely across foot.
Sinus tarsi – laterally, large end, anterior to the fibular
malleolus.
Sustentaculum tali – medially, small end, below tibial
malleolus & above calcaneus.
Ligaments running through, divides posterior
articulation from anterior & medial articulations.
Posterior has its own capsule whereas anterior & medial
articulations share capsule with talonavicular joint.
35. LIGAMENTS
All ligaments of ankle joint.
Other ligaments –
Calcaneofibular ligament
Lateral talocalcaneal ligament
Cervical ligament
Strongest ligament
Interosseus talocalcaneal ligament
Has anterior & posterior bands
36. FUNCTION
3 articulations – alternating convex-concave – limits
potential mobility of joint.
Motion of talus on calcaneus is complex twisting or
screw like motion that proceeds till the facets can
accommodate simultaneous & opposite motions
across the surfaces.
Triplanar motion – around a single oblique joint axis
– supination / pronation.
37. Cont…
The subtalar axis –
TP
SP
Component motions; can’t
occur independently.
Includes about equal
magnitude of
eversion/inversion &
abduction/adduction but
a very small component of
dorsiflexion/
plantarflexion.
39. MITERED HINGE –
Representation of interdependence of leg & foot
40. RANGE
Difficult to determine objectively because of
triplanar nature of movement & as the component
contribution vary with inclination of subtalar joint.
Normally calcaneal eversion (valgus) is 5-10 &
inversion is 20-30 degrees. (usually easy to measure
component)
Dorsi/plantarflexion can’t be assessed properly
except static radiograph; abduction/adduction even
difficult on radiogram so can be estimated by degree
of tibial rotation.
Change in inclination in subtalar joint axis, changes
ROM of component movements & affect both foot &
leg position in weight bearing.
41. Subtalar neutral position – point from which
calcaneus will invert twice of eversion. (Root &
colleagues)
The main function of subtalar joint in weight bearing
is to absorb the imposed lower extremity transverse
plane rotations that occur during walking & other
weight bearing activities.
43. Also called as mid-tarsal or Chopart joint.
Compound joint formed by –
Talonavicular joint &
Calcaneo-cuboid joint
S-shaped joint line – transects foot horizontally –
divides hindfoot from midfoot & forefoot.
During weight bearing, navicular & cuboid bones are
considerably immobile – so talus & calcaneus has to
move on relatively fixed naviculo-cuboid unit.
44. Talonavicular joint
Proximal articulation by anterior portion of head of
talus (convex) & distal by concave posterior aspect of
navicular bone.
Ball & socket joint
Shares joint capsule with anterior & medial facets of
subtlar joint.
Inferior aspect of capsule is formed by plantar
calcaneonavicular (spring) ligament.
Capsule is reinforced medially by deltoid & laterally
by bifurcate ligament.
45. Cont…
Spring ligament –
Triangular sheet from
sustentaculum tali to inferior
navicular bone.
Continuous medially with
deltoid ligament & laterally
with medial band of bifurcate
ligament.
Little or no elasticity; resist
tensile stresses.
Supports head of talus &
talonavicular joint.
Provides support to medial
longitudinal arch.
46. Cont…
During weight bearing, talonavicular joint is linked to the
subtalar joint.
In weight bearing supination & pronation, talus moves
on calcaneus that causes movement of talus on navicular
bone.
The talonavicular joint & subtalar joint are anatomically
& functionally related in weight bearing.
Ligaments reinforcing talonavicular joint –
Spring & bifurcate ligament
Dorsal talonavicular ligament
MCL & LCL
Inferior extensor retinaculum
Cervical & interosseous talocalcaneal ligament
47. Calcaneo-cuboid joint
Formed proximally by anterior calcaneus & distally
by posterior cuboid bone.
Articular surfaces are complex; reciprocally
concave/convex both side to side & top to bottom –
restricts motion.
Saddle joint
Linked to subtalar joint in weight bearing.
Has own capsule.
48. Cont…
Reinforced by several ligaments –
Laterally by lateral band of bifurcate ligament (calcaneocuboid
Ligament)
Dorsally by dorsal calcaneocuboid ligament
Inferiorly by plantar calcaneocuboid ligament (short plantar)
& long plantar ligament.
Long plantar ligament –
Most important
Significant contribution to transverse tarsal joint stability & to
related support of the lateral longitudinal arch of foot.
49. Transverse tarsal joint axis
Movements are more difficult to study because multiple
joints & axes are involved.
Talonavicular and calcaneocuboid joints have some
independent movement, but motion at one is generally
accompanied by at least some motion of the other
because of their functional, bony, and ligamentous
connections.
The longitudinal axis is nearly horizontal, being inclined
15 upward from the transverse plane and angled 9
medially from the sagittal plane.
Triplanar movement, predominated by inversion /
eversion.
51. The oblique (transverse) axis of the transverse tarsal
joint is positioned approximately 57 medial to the sagittal
plane and 52 superior to the transverse plane.
This triplanar axis also provides supination/pronation
with coupled component movements of the talus and
calcaneus segments moving together on the navicular
and cuboid bones, but dorsiflexion/plantarflexion and
abduction/adduction components predominate.
Motions about the longitudinal and oblique axes are
difficult to separate and to quantify.
The longitudinal and oblique axes together provide a
total range of supination/pronation of the talus and
calcaneus that is about one third to one half of the range
available at the subtalar joint.
53. Transverse tarsal joint function
Function similar to that of the subtalar joint.
The subtalar and the transverse tarsal joints are
linked mechanically.
Any weight-bearing subtalar motion causes motion
at the talonavicular joint and the calcaneocuboid
joint.
As the subtalar joint supinates/pronates, its linkage
to the transverse tarsal joint causes both the
talonavicular joint and the calcaneocuboid joint to
begin to supinate/pronate also.
54. The transverse tarsal joint is the transitional link
between the hindfoot and the forefoot, & serves to
add to the supination/pronation range of the subtalar joint
and
compensate the forefoot for hindfoot position.
Compensation refers to the ability of the forefoot to
remain flat on the ground while the hindfoot (talus
and calcaneus) pronates or supinates in response to
the terrain or the rotations imposed by the leg.
55. Weight-Bearing Hindfoot Pronation and Transverse
Tarsal Joint Motion –
In the weight-bearing position, during pronation on the subtalar
joint; if the force continued distally through the foot, the lateral
border of the foot tends to lift from the ground, diminishing the
stability of the base of support, resulting in unequal weight-bearing,
and imposing stress at multiple joints.
This undesirable effect of weight-bearing subtalar joint pronation
may be avoided if the forefoot remains flat on the ground.
This can occur if the transverse tarsal joint is mobile and can
effectively “absorb” the hindfoot pronation.
Relative supination of the bony segments distal to the transverse
tarsal joint, with the result that the forefoot remains relatively flat
on the ground.
When the weight-bearing hindfoot (subtalar joint) is pronated – the
transverse tarsal joint will supinate.
56. Weight-Bearing Hindfoot Supination and Transverse
Tarsal Joint Motion
A lateral rotatory force on the leg will create subtalar supination
in the weight-bearing subtalar joint with a relative pronation of
the transverse tarsal joint.
Transverse tarsal joint mobility is increasingly limited as the
subtalar joint moves toward full supination.
the transverse tarsal joint cannot absorb the additional rotation
but begins to move toward supination as well.
58. The tarsometatarsal (TMT) joints are plane synovial joints
formed by the distal row of tarsal bones (posteriorly) and the
bases of the metatarsals .
The first (medial) TMT joint is composed of the articulation
between the base of the first metatarsal and the medial
cuneiform bone and has its own articular capsule.
The second TMT joint is composed of the articulation of the
base of the second metatarsal with a mortise formed by the
middle cuneiform bone and the sides of the medial and lateral
cuneiform bones. This joint is set more posteriorly than the
other TMT joints; it is stronger and its motion is more
restricted.
The third TMT joint, formed by the third metatarsal and the
lateral cuneiform, shares a capsule with the second TMT joint.
The bases of the fourth and fifth metatarsals, with the distal
surface of the cuboid bone, form the fourth and fifth TMT
joints. These two joints also share a common joint capsule.
59. Small plane articulations exist between the bases of
the metatarsals to permit motion of one metatarsal
on the next.
Ligaments reinforcing TMT joint -
Numerous dorsal, plantar, and interosseous ligaments
Deep transverse metatarsal ligament - spans the heads of the
metatarsals on the plantar surface & so contributes to
stability of the proximally located TMT joints by preventing
excessive motion and splaying of the metatarsal heads.
60. Axes
Each TMT joint is considered to have a unique, although not
fully independent, axis of motion.
A ray is defined as a functional unit formed by a metatarsal
and (for the first through third rays) its associated cuneiform
bone.
The cuneiform bones are included as parts of the movement
units of the TMT rays because of the small and relatively
insignificant amount of motion occurring at the
cuneonavicular joints.
The fourth and fifth rays are formed by the metatarsal alone
because these metatarsals share an articulation with the
cuboid bone.
most motion at the TMT joints occurs at the first and fifth
rays.
Each axis is oblique and, therefore, triplanar.
The first has the largest ROM.
61. The axis of the first ray is inclined in such a way that
dorsiflexion of the first ray also includes inversion and
adduction, whereas plantarflexion is accompanied by eversion
and abduction.
The abduction/adduction components normally are minimal.
Movements of the fifth ray around its axis are more restricted
and occur with the opposite arrangement of components:
dorsiflexion is accompanied by eversion and abduction, and
plantarflexion is accompanied by inversion and adduction.
The axis for the third ray nearly coincides with a coronal axis;
the predominant motion, therefore, is
dorsiflexion/plantarflexion.
The axes for the second and fourth rays were considered to be
intermediate between the adjacent axes for the first and fifth
rays, respectively.
62. Function
The motions of the TMT joints are interdependent.
TMT joints contribute to hollowing and flattening of the foot.
The greatest relevance of TMT joint motions is found during weight-
bearing.
In weightbearing, the TMT joints function primarily to augment the
function of the transverse tarsal joint; (attempt to regulate position
of the metatarsals and phalanges in relation to the weight-bearing
surface).
As long as transverse tarsal joint motion is adequate to compensate
for the hindfoot position, considerable TMT joint motion is not
required.
However, when the hindfoot position is at an end point in its
available ROM or the transverse tarsal joint is inadequate to provide
full compensation, the TMT joints may rotate to provide further
adjustment of forefoot position.
63. Supination twist
When the hindfoot pronates in weightbearing, the transverse tarsal
joint generally supinate to some degree to counterrotate the forefoot
and keep the plantar aspect of the foot in contact with the ground.
If the range of transverse tarsal supination is not sufficient to meet
the demands of the pronating hindfoot, the medial forefoot will
press into the ground, and the lateral forefoot will tend to lift.
The first and second ray will be pushed into dorsiflexion by the
ground reaction force, and the muscles controlling the fourth and
fifth rays will plantarflex the TMT joints in an attempt to maintain
contact with the ground.
Both dorsiflexion of the first and second rays and plantarflexion of
the fourth and fifth rays include the component motion of inversion
of the ray.
Consequently, the entire forefoot undergoes an inversion rotation
around a hypothetical axis at the second ray. This rotation is
referred to as supination twist of the TMT joints.
64. Pronation twist
When both the hindfoot and the transverse tarsal joints are
locked in supination, the adjustment of forefoot position must
be left entirely to the TMT joints.
With hindfoot supination, the forefoot tends to lift off the
ground on its medial side and press into the ground on its
lateral side.
The muscles controlling the first and second rays will cause
the rays to plantarflex in order to maintain contact with the
ground, whereas the fourth and fifth rays are forced into
dorsiflexion by the ground reaction force.
Because eversion accompanies both plantarflexion of the first
and second rays and dorsiflexion of the fourth and fifth rays,
the forefoot as a whole undergoes a pronation twist.
66. The five metatarsophalangeal (MTP) joints are condyloid
synovial joints with two degrees of freedom: extension/
flexion (or dorsiflexion/plantarflexion) and
abduction/adduction.
Although both degrees of freedom might be useful to the
MTP joints in the rare instances when the foot
participates in grasplike activities, flexion and extension
are the predominant functional movements at these
joints.
During the late stance phase of walking, toe extension at
the MTP joints permits the foot to pass over the toes,
whereas the metatarsal heads and toes help balance the
superimposed body weight through activity of the
intrinsic and extrinsic toe flexor muscles.
67. Structure
The MTP joints are formed proximally by the convex heads of
the metatarsals and distally by the concave bases of the
proximal phalanges.
The range of MTP extension exceeds the range of MTP flexion.
All metatarsal heads bear weight in stance.
Consequently, the articular cartilage must remain clear of the
weight-bearing surface on the plantar aspect of the metatarsal
head.
This structural requirement restricts the available range of
MTP flexion.
The first MTP joint has two sesamoid bones associated with it
that are located on the plantar aspect of the first metatarsal
head .
In the neutral position of the first MTP joint, the sesamoid
bones lie in two grooves on the metatarsal head that are
separated by the intersesamoid ridge.
68. The ligaments associated with the sesamoid bones form a
triangular mass that stabilizes the sesamoid bones within
their grooves.
The sesamoid bones serve as anatomic pulleys for the flexor
hallucis brevis muscle and protect the tendon of the flexor
hallucis longus muscle from weight-bearing trauma as the
flexor hallucis longus passes through a tunnel formed by
the sesamoid bones and the intersesamoidal ligament that
connects the sesamoid bones across their plantar surfaces.
In toe extension greater than 10, the sesamoid bones no
longer lie in their grooves and may become unstable.
Chronic lateral instability of the sesamoid bones may lead
to MTP deformity.
69. Stability of the MTP joints is provided by a joint capsule,
plantar plates, collateral ligaments, and the deep transverse
metatarsal ligament.
The plantar plates are the fibrocartilaginous structures in
the four lesser toes that are connected to the base of the
proximal phalange distally and blend with the joint capsule
proximally.
The plates of the four lesser toes are interconnected by the
deep transverse metatarsal ligament and by the plantar
aponeurosis.
70. The collateral ligaments of the MTP joints, have two
components:
a phalangeal portion that parallels the metatarsal and phalange, and
an accessory component that runs obliquely from the metatarsal
head to the plantar plate.
The plantar plates protect the weight bearing surface of
the metatarsal heads and, with the collateral ligaments,
contribute to stability of the MTP joints.
Long flexor tendons run in grooves in the plates that help
maintain tendon position as the MTP joints are crossed.
At the first MTP joint, the sesamoid bones and thick
plantar capsule are in place of the plantar plates found at
the other toes.
71. Function
The MTP joints have two degrees of freedom, but
flexion/extension motion is much greater than
abduction/adduction motion, and extension exceeds
flexion.
Although MTP motions can occur in weight-bearing or
non–weight-bearing, the MTP joints serve primarily to
allow the weight-bearing foot to rotate over the toes
through MTP extension (known as the metatarsal break)
when rising on the toes or during walking.
72. MTP extension & metatarsal break
The metatarsal break derives its name from the hinge or “break” that
occurs at the MTP joints as the heel rises and the metatarsal heads and
toes remain weight bearing.
The metatarsal break occurs as MTP extension around a single oblique
axis that lies through the second to fifth metatarsal heads.
The range of MTP extension will also vary somewhat, depending on the
relative lengths of the metatarsals and whether the motions occur in
weight-bearing or non–weight-bearing activities.
Limited extension ROM at the first MTP joint will interfere with the
metatarsal break and is known as hallux rigidus.
The obliquity of the axis for the metatarsal break allows weight to be
distributed across the metatarsal heads and toes more evenly than
would occur if the axis were truly coronal.
74. MTP flexion, abduction & adduction
Flexion ROM at the MTP joints can occur to a limited degree from
neutral position but has relatively little purpose in the weight-bearing
foot other than when the supporting terrain drops away distal to the
metatarsal heads.
Abduction and adduction of the MTP joint appear to be helpful in
absorbing some of the force that would be imposed on the toes by the
metatarsals as they move in a pronation or supination twist.
An increase in this normal valgus angulation of the first MTP joint is
referred to as hallux valgus and may be associated with a varus
angulation of the first metatarsal at the TMT joint, known as
metatarsus varus.
76. Synvial hinge joints with one degree of freedom : flexion/ extension
Great toe has only one IP joint whereas lesser toes has 2 IP joints
The toes function to smooth the weight shift to the opposite foot in gait
& help maintain stability by pressing against the ground in standing.
78. The foot typically is characterized as having three arches: medial and
lateral longitudinal arches and a transverse arch, of which the medial
longitudinal arch is the largest.
The arches are fully integrated with one another and enhance the
dynamic function of the foot.
The arches are not present at birth but evolve with the progression of
weight-bearing.
By 5 years of age, as children approached gait parameters similar to
those of adults, the majority of children had developed an adult like
arch.
79. Structure of arches
The longitudinal arches are anchored posteriorly at the calcaneus and
anteriorly at the metatarsal heads; the arch is higher medially, than
laterally so the medial side usually is the side of reference.
The talus rests at the top of the vault of the foot and is considered to be
the “keystone” of the arch. All weight transferred from the body to the
heel or the forefoot must pass through the talus.
The transverse arch, At the anterior tarsals, the middle cuneiform bone
forms the keystone of the arch.
80. The shape and arrangement of the bones are partially responsible for
stability of the plantar arches.
The wedge-shaped mid tarsal bones provide an inherent stability to the
transverse arch.
The inclination of the calcaneus and first metatarsal contribute to
stability of the medial longitudinal arch, particularly in standing.
82. Although the structure of the tarsal bones provides a certain inherent
stability to the arches, the arches would collapse without additional
support from ligaments and muscles.
Because the three arches can be thought of as a segmented vault or one
continuous set of interdependent linkages, support at one point in the
system contributes to support throughout the system.
83. The plantar calcaneonavicular (spring) ligament, the interosseous
talocalcaneal ligament, and the plantar aponeurosis have been credited
with providing key passive support to the arch.
The cervical ligament is credited with contributing particularly
important support of the posterior aspect of the longitudinal arch.
Support from the more laterally located long and short plantar
ligaments appeared to be important but less influential than support
from the spring and cervical ligaments.
84.
85. Function of arches
The plantar arches are adapted uniquely to serve two contrasting
mobility and stability weight-bearing functions.
First, the foot must accept weight during early stance phase and adapt
to various surface shapes.
To accomplish this weight-bearing mobility function, the plantar arches
must be flexible enough to allow the foot to
Dampen the impact of weight-bearing forces
Dampen superimposed rotational motions
Adapt to changes in the supporting surface.
To accomplish weight-bearing stability functions, the arches must allow
Distribution of weight through the foot for proper weight-bearing
Conversion of the flexible foot to a rigid lever.
86. Plantar aponeurosis
The role of the plantar aponeurosis (the plantar fascia) is particularly
important.
The plantar aponeurosis is a dense fascia that runs nearly the entire
length of the foot.
It begins posteriorly on the medial tubercle of the calcaneus and
continues anteriorly to attach by digitations to the plantar plates and
then, to the proximal phalanx of each toe.
From the beginning to the end of the stance phase of gait, tension on
the plantar aponeurosis increases.
87. For this reason, the function of the aponeurosis in supporting the
arches has been compared to the function of a tie-rod on a truss.
The truss and the tie-rod form a triangle; the two struts of the truss
form the sides of the triangle and the tie-rod is the bottom.
The talus and calcaneus form the posterior strut, and the remaining
tarsal and metatarsals form the anterior strut.
The plantar aponeurosis, as the tie-rod, holds together the anterior and
posterior struts when the body weight is loaded on the triangle.
88. This structural design is efficient for the weight-bearing foot because
the struts (bones) are subjected to compression forces, whereas the tie-
rod (aponeurosis) is subjected to tension forces.
The fibrocartilaginous plantar plates of the MTP joints are organized
not only to resist compressive forces from weight-bearing on the
metatarsal heads but also to resist tensile stresses presumably applied
through the tensed plantar aponeurosis. Therefore, each biological
structure is positioned to maximize its optimal loading pattern and
minimize the opportunity for injury.
89.
90. When the toes are extended at the MTP joints the plantar aponeurosis
is pulled increasingly tight as the proximal phalanges glide dorsally in
relation to the metatarsals or as the metatarsal heads glide in a
relatively plantar direction on the fixed toes.
The metatarsal heads act as pulleys around which the plantar
aponeurosis is pulled and tightened.
As the plantar aponeurosis is tensed with MTP extension, the heel and
MTP joint are drawn toward each other as the tie-rod is shortened,
raising the arch and contributing to supination of the foot.
91. This phenomenon allows the plantar aponeurosis to increase its role in
supporting the arches as the heel rises and the foot rotates around the
MTP joints in weight-bearing (during the metatarsal break).
The reduction in tension in the plantar aponeurosis will allow an
increase in the range of MTP extension.
Through the pulley effect of the MTP joints on the plantar aponeurosis,
it acts interdependently with the joints of the hindfoot to contribute to
increasing the longitudinal arch.
92. The tightened plantar aponeurosis also increases the passive flexor
force at the MTP joints, preventing excessive toe extension that might
stress the MTP joint or allow the LoG to move anterior to the toes.
Finally, the passive flexor force of the tensed plantar aponeurosis also
assists the active toe flexor musculature in pressing the toes into the
ground to support the body weight on its limited base of support.
93. Weight distribution
Because the foot is a flexible rather than fixed arch, the distribution of
body weight through the foot depends on many factors, including the
shape of the arch and the location of the LoG at any given moment.
The pattern of weight distribution through the foot can be seen by
looking at the trabeculae in the bones of the foot.
In static standing, the distribution of weight-bearing on the plantar foot
is highly variable and depends on a number of postural and structural
factors.
Load distribution analysis during quiet standing showed that the heel
carried 60%, the midfoot 8%, and the forefoot 28% of the weight
bearing load. The toes were minimally involved in bearing weight.
Plantar pressures are much greater during walking than during
standing, with the highest pressures typically under the metatarsal
heads and occurring during the push-off phase of walking (~80% of
stance), when only the forefoot is in contact with the ground and is
pushing to accelerate the body forward.
96. Excessive plantar pressures can contribute to pain and injury in otherwise
healthy people or contribute to skin breakdown in patients with diabetes
and peripheral neuropathy.
Pressure under the first metatarsal head also increases as arch height
increases.
As one might expect, the soft tissue under the forefoot and the heel acts as a
cushion, and as this soft tissue thickness decreases, pressures increase.
The greatest stresses to the heel during walking occur at heel strike and
typically are 85% to 130% of body weight.
Running with a heel contact pattern increases this force to 220% of body
weight.
The heel pad is composed of fat cells that are located in chambers formed
by fibrous septa attached to the calcaneus above and the skin below.
The effectiveness of the cushioning action of the heel pad decreases with
age and with concomitant loss of collagen, elastic tissue, and water.
97. Muscular Contribution to the Arches
Muscle activity appears to contribute little to arch support in the
normal static foot.
The small intrinsic muscles of the foot contract periodically during
quiet stance, presumably to provide brief periods of unloading for the
many ligaments supporting the foot.
Key muscular support is provided to the medial longitudinal arch
during gait is by tibialis posterior, the flexor digitorum longus, and the
flexor hallucis longus muscles.
The peroneus longus muscle provides important lateral stability as
These medial and lateral muscles provide a dynamic sling to support
the arches of the foot during the entire stance phase of walking and
enhance adaptation to uneven surfaces.
