Biomechanics

1. Regional biomechanics of the ankle
and foot joint
Dr.Ahmed Mohamed Mostafa
LECTURER OF PHYSICALTHERAPY FOR PEDIATRICS
FACULTY OF PHYSICALTHERAPY
MERIT UNIVERSITY.

2. Up to 14 named joints or joint complexes are
structurally or functionally associated with the ankle
and foot. the interaction of three major joints:
Talocrural, Subtalar, and Transverse tarsal.
Ankle and Foot

3. Fundamental movement
➢Movement of the foot or ankle as occurring at right angles to the
three standard axes of rotation. Dorsiflexion (extension) and plantar
flexion describe motion that is parallel to the sagittal plane, around a
medial-lateral axis of rotation. Eversion and inversion describe motion
that is parallel to the frontal plane, around an anterior-posterior axis
of rotation. Abduction and adduction describe motion that is parallel
to the horizontal (transverse) plane, around a vertical (superior-
inferior) axis of rotation.
Applied movement
➢Movements that occur perpendicular to the prevailing oblique axes of
rotation at the ankle and foot. Pronation is defined as a motion that
has elements of eversion, abduction, and dorsiflexion. Supination, in
contrast, is defined as a motion that has elements of inversion,
adduction, and plantar flexion. Pronation and supination motions
have been called “tri-planar” motions.

5. Tibiofibular joint
•Proximal tibiofibular joint
- The proximal (or superior) tibiofibular joint is a synovial joint. The joint is formed
between the head of the fibula and the posterior-lateral aspect of the lateral condyle of
the tibia
- When stressed by forces and torques generated while walking, 1–3 mm of anterior and
posterior translations. The relative stability by forces from the biceps femoris and
lateral collateral ligament of the knee.
•DISTAL TIBIOFIBULAR JOINT
- The distal tibiofibular joint is formed by the articulation between the medial surface of
the distal fibula and the fibular notch of the tibia. Anatomists frequently refer to the
distal tibiofibular joint as a syndesmosis, which is a type of fibrous synarthrodial joint
that is closely bound by an interosseous membrane. A stable union between the distal
tibia and fibula is essential to the stability and function of the talocrural joint.

6. Talocrural joint
• The talocrural joint, or ankle, is the articulation of the trochlea of the
talus with the rectangular cavity formed by the distal end of the tibia
and both malleoli
• The confining shape of the talocrural joint provides a major source of
natural stability to the ankle
• The structure of the mortise must be sufficiently stable to accept the
forces that pass between the leg and foot. While standing
approximately 90% to 95% of the compressive forces pass through the
talus and tibia; the remaining 5% to 10% pass through the lateral
region of the talus and the fibula
• Many of the components of the ligaments that cross the talocrural
joint also cross other joints of the foot, such as the subtalar and
talonavicular joints. These ligaments provide stability across multiple
joints.

7. Osteokinematics
• The talocrural joint has one degree of freedom.
• The axis deviates from a pure medial-lateral axis by about 10 degrees in the
frontal plane and 6 degrees in the horizontal plane. Because the lateral malleolus
is inferior and posterior to the medial malleolus.
• Because of the pitch of the axis of rotation, dorsiflexion is associated with slight
abduction and eversion, and plantar flexion with slight adduction and inversion
• The horizontal and frontal plane components of pronation and supination are
indeed small and ignored in most clinical situations.
• The 0-degree (neutral) position at the talocrural joint is defined by the foot held
at 90 degrees to the leg. From this position, the talocrural joint permits about 15
to 25 degrees of dorsiflexion and 40 to 55 degrees of plantar flexion,
• The fully dorsiflexed talocrural joint is the close-packed position

9. Arthrokinematics
•During dorsiflexion, the talus rolls forward relative to the leg
as it simultaneously slides posteriorly
• The simultaneous posterior slide allows the talus to rotate
forward with only limited anterior translation
• During plantar flexion, the talus rolls posteriorly as the bone
simultaneously slides anteriorly

11. Factors that increase the mechanical stability of the fully dorsiflexed talocrural
joint (A) The increased passive tension in several connective tissues and muscles. (B) The
trochlear surface of the talus is wider anteriorly than posteriorly (see red line). The path of
dorsiflexion places the concave tibiofibular segment of the mortise in contact with the
wider anterior dimension of the talus. The slight natural spreading of the mortise at
maximal dorsiflexion causes slight rotational and translational movement of the fibula.

12. The Foot
• SUBTALAR JOINT
• Pronation and supination during non–weight-bearing activities
occur as the calcaneus moves relative to the fixed talus. During
weight-bearing activities, such as when in the stance phase of
walking, pronation and supination occur as the leg and talus (as a
common unit) rotate over a relatively stationary (fixed) calcaneus.
• These weight-bearing–based kinematics of the subtalar joint are
essential to allow the foot to assume positions that are independent
of the orientation of the superimposed ankle and leg. This function
is essential to activities such as walking across a steep hill, standing
with the feet held wide apart, quickly changing directions while
walking or running, and keeping one’s balance on a rocking boat.

13. • The arthrokinematics at the subtalar joint involve a sliding motion
among the three sets of facets, yielding a curvilinear arc of
movement between the calcaneus and the talus
• The axis of rotation is typically described as a line that pierces the
lateral-posterior heel and courses through the subtalar joint in
anterior, medial, and superior directions. The axis of rotation is
positioned 42 degrees from the horizontal plane and 16 degrees from
the sagittal plane
• Pronation and supination of the subtalar joint occur as the calcaneus
moves relative to the talus (or vice versa when the foot is planted) in
an arc that is perpendicular to the axis of rotation
• Two of the three main components of pronation and supination are
strongly evident: inversion and eversion, and abduction and
adduction

15. Transverse tarsal joint (talonavicular and calcaneocuboid joints)
• The transverse tarsal joint, also known as the Midtarsal or Chopart’s joint,
consists of two anatomically distinct articulations: the talonavicular joint
and the calcaneocuboid joint, these joints connect the rearfoot with the
midfoot.
• Pronating and Supinating the midfoot. During these motions the navicular
spins within the talonavicular joint.
• Three points should be made when analyzing the kinematics of the
transverse tarsal joint:
• First: two separate axes of rotation have been identified.
• Second: the amplitude and direction of movement are typically different
during weight-bearing as compared with non–weight-bearing activities.
• Third: the kinematics of the transverse tarsal joint are functionally
influenced by the position of the subtalar joint.

16. Axes of Rotation and Corresponding Movements
•Two axes of rotation for movement at the transverse
tarsal joint: longitudinal and oblique
•The longitudinal axis at the transverse tarsal joint is
nearly coincident with the straight anterior-posterior
axis, with the primary component motions of eversion
and inversion
•The oblique axis, has a strong vertical and medial-lateral
pitch. Motion around this axis, therefore, occurs freely as
a combination of abduction and dorsiflexion, and
adduction and plantar flexion

19. •Arthrokinematics
• Describe the arthrokinematics at the transverse tarsal joint motion across
both the rearfoot and the midfoot.
• Consider the movement of active supination of the unloaded foot. The
tibialis posterior muscle, with its multiple attachments, is the prime
supinator of the foot. Because of the relatively rigid calcaneocuboid joint,
an inverting and adducting calcaneus draws the lateral column of the foot
“under” the medial column of the foot. The important pivot point for this
motion is the talonavicular joint. The pull of the tibialis posterior contributes
to the spin of the navicular, and the raising of the medial longitudinal arch
(instep) of the foot. During this motion, the concave proximal surface of the
navicular and the spring ligament both spin around the convex head of the
talus.
•Pronation of the unloaded foot occurs by similar but reverse kinematics
as those described. The pull of the fibularis longus helps lower the medial
side and raise the lateral side of the foot.

20. The transverse tarsal joints allow for pronation and supination of the
midfoot while one stands on uneven surfaces.

21. Medial Longitudinal Arch of the Foot
• This arch is the Primary load-bearing and Shock-absorbing structure
of the foot.
• The bones that contribute structurally to the medial longitudinal arch
include the calcaneus, talus, navicular, cuneiforms, and associated three
medial metatarsals.
• Connective tissues help maintain the shape of the medial arch.
• Structures that assist the arch in absorbing loads are the plantar fat
pads, sesamoid bones located at the plantar base of the big toe, and
plantar fascia

22. •Connective tissues are the primary sources of mechanical
support for the foot during low-stress or near-static
conditions as quiet standing.
•Muscular force are required when the arch is stressed by
larger or dynamic loading, such as standing on tiptoes,
walking, jumping, or running.

23. Passive Support Mechanism of the Medial Longitudinal Arch
• The talonavicular joint and associated connective tissues form the
keystone of the medial longitudinal arch.
• Non-muscular structures responsible for maintaining the height and
general shape of the arch are the plantar fascia, spring ligament, and first
tarsometatarsal joint.
• The plantar fascia of the foot provides the primary passive support to the
medial longitudinal arch. The fascia is extremely strong, capable of
resisting approximately 810 N (over 180 lb.) of tension before permanent
elongation

24. •Tension in stretched connective tissues
• The deep plantar fascia, acts as a semi-elastic tie-rod that supports, absorbs
body weight, and maintains the height of the medial longitudinal arch
• As the arch is depressed, the rearfoot normally pronates a few degrees.
• Active muscle support while quiet standing is relatively small and variable, and
may be considered as a “secondary line of support”—for example, for
controlling postural sway, switching from double to single limb support,
supporting relatively heavy loads, or when the arch lacks inherent support
because of overstretched or weakened connective tissues.

25. When one stands normally, the weight
of the body falls through the foot near
the region of the talonavicular joint.
This load is distributed anteriorly and
posteriorly throughout the medial
longitudinal arch, passing to the fat
pads and the thick dermis over the heel
and ball (metatarsal head region) of the
foot.
Normally the rearfoot receives about
twice the compressive load as the
forefoot. The mean pressure under the
forefoot is usually greatest in the region
of the heads of the second and third
metatarsal bones.

27. Navicular drop test
• During standing, body weight pushes the talus inferiorly, slightly
lowering the medial longitudinal arch. The amount of depression
of the arch while weight bearing can be measured clinically by the
distance between the ground and the navicular tuberosity
• The drop of the arch (on average about 7 mm in healthy adult
males) increases the distance between the calcaneus and
metatarsal heads.

28. The combined action of the subtalar and transverse
tarsal joints
• When the foot is unloaded (i.e., non-weight bearing), pronation twists the sole outward,
whereas supination twists the sole inward.
• While the foot is under load during the stance phase of walking, pronation and
supination permit the leg and talus to rotate in all three planes relative to a
comparatively fixed calcaneus. This important mechanism is orchestrated through
interaction among the subtalar joint, transverse tarsal joint, and medial longitudinal arch.
✓Early to midstance phase of gait: kinematics of pronation at the subtalar joint
✓Mid-to-late stance phase of gait: kinematics of supination at the subtalar joint
• This load attenuation mechanism offers essential protection to the foot and lower limb
against stress-related, overuse injury

29. Early to midstance phase of gait: kinematics of
pronation at the subtalar joint
The pronation (eversion) at the subtalar joint during stance occurs by two
mechanisms.
• First: The calcaneus tips into slight eversion in response to the ground
reaction force passing just lateral to the midpoint of the calcaneus, pushing
the head of the talus medially in the horizontal plane and inferiorly in the
sagittal plane. Relative to the calcaneus, this motion of the talus abducts
and (slightly) dorsiflexes the subtalar joint. These motions are consistent
with the formal definition of pronation.
• Second: during the early stance phase, the tibia and fibula, and to a lesser
extent the femur, internally rotate after initial heel contact. Because of the
configuration of the talocrural joint, the internally rotating lower leg steers
the subtalar joint into further pronation. The argument is often made that
with the calcaneus in contact with the ground, pronation at the subtalar
joint causes, rather than follows, internal rotation of the leg

30. With the foot fixed, full internal
rotation of the lower limb is
mechanically associated with
rearfoot pronation (eversion),
lowering of the medial
longitudinal arch, and valgus
stress at the knee.
Note that as the rearfoot
pronates, the floor “pushes” the
forefoot and midfoot into a
relatively supinated position.

32. Biomechanical Benefits of Controlling Pronation during
the Stance Phase
• Pronation at the subtalar joint permits the talus and entire lower extremity
to rotate internally slightly after the calcaneus has contacted the ground. The
strong horizontal orientation of the facets at the subtalar joint certainly
facilitates this action. Eccentric activation of supinator muscles, mainly the
tibialis posterior, can help to decelerate the pronation and resist the
lowering of the medial longitudinal arch. Controlled pronation of the
subtalar joint favors relative flexibility of the midfoot, allowing the foot to
accommodate to the varied shapes and contours of walking surfaces.

33. Mid-to-late stance phase of gait: kinematics of
supination at the subtalar joint
• With the stance foot securely planted, external rotation of the femur,
followed by the tibia, gradually reverses the horizontal plane direction
of the talus from internal to external rotation. As a result, the pronated
(everted) subtalar joint starts to move toward supination (inversion),
with the rearfoot supinating, the midfoot and forefoot must
simultaneously twist into relative pronation in order for the foot to
remain in full contact with the ground.
• By late stance, the supinated subtalar joint and the elevated and
tensed medial longitudinal arch convert the midfoot (and ultimately
the forefoot) into a more rigid lever. Muscles such as the
gastrocnemius and soleus use this stability to transfer forces from the
Achilles tendon, through the midfoot, to the metatarsal heads during
the push off phase of walking or running.

34. With the foot fixed to the ground,
full external rotation of the lower
limb is mechanically associated
with rearfoot supination
(inversion) and raising of the
medial longitudinal arch.
Note that as the rearfoot
supinates, the forefoot and
midfoot pronate to maintain
contact with the ground.

35. Distal intertarsal joints
Basic Function
(1) Assist the transverse tarsal joint in pronating and supinating the midfoot
(2) Provide stability across the midfoot by forming the transverse arch of the
foot.
• Cuneonavicular Joint: Three articulations are formed between the anterior
side of the navicular and the posterior surfaces of the three cuneiform bones.
The major function is to help transfer components of pronation and supination
distally from the talonavicular toward the forefoot.
• Cuboideonavicular Joint: The small synarthrodial (fibrous) or sometimes
synovial, the articular surfaces slide slightly against each other during movements
of the midfoot, most notably during inversion and eversion.
• Intercuneiform and Cuneocuboid Joint Complex: forms the transverse
arch of the foot. This arch provides transverse stability to the midfoot. Under the
load of body weight, the transverse arch depresses slightly. The transverse arch
receives support from intrinsic muscles; extrinsic muscles, such as the tibialis
posterior

36. Structural features of the midfoot and forefoot.
(A) The transverse arch is formed by the
intercuneiform and cuneocuboid joint complex.
(B) The stable second ray is reinforced by the
recessed second tarsometatarsal joint.
(C) Combined plantar flexion and eversion of the left
tarsometatarsal joint of the first ray allow the
forefoot to better conform to the surface of the rock.

37. Tarsometatarsal joints (Lisfranc’s joints)
• The five tarsometatarsal joints separate the midfoot from the forefoot. The joints
consist of the articulation between the bases of the metatarsals and the distal
surfaces of the three cuneiforms and cuboid.
• Mobility is greatest in the first, fourth, and fifth tarsometatarsal joints
• Mobility is least at the second and third tarsometatarsal joints
• During the early to midstance phase of walking, the first tarsometatarsal
joint (or entire medial column of the foot) dorsiflexes about 5 degrees, This
motion occurs as body weight depresses the cuneiform region downward. This
movement is associated with a gradual lowering of the medial longitudinal arch,
that helps absorb the stress of body weight acting on the foot.
• At the late stance (push off ) phase of gait, the first tarsometatarsal joint
rapidly plantar flexes about 5 degrees. The plantar flexion of the first ray,
controlled in part by pull of the fibularis longus, helping to raise the medial
longitudinal arch. This mechanism increases the stability of the arch (and medial
column of the foot) at a time in the gait cycle when the midfoot and forefoot are
under higher loads

38. The osteokinematics of the first tarsometatarsal joint. Plantar flexion occurs with
slight eversion (A), and dorsiflexion occurs with slight inversion (B).

39. Muscle and joint interaction

42. EXTRINSIC MUSCLES
•The pretibial muscles (tibialis anterior and extensor hallucis longus)
are most active during the early stance phase and again throughout
the entire swing phase of gait.
➢During early stance: the muscles are eccentrically active to control the
rate of plantar flexion. Controlled plantar flexion is necessary for a soft
landing of the foot. Through similar eccentric activation, the tibialis
anterior helps to decelerate the lowering of the medial longitudinal
arch and therefore indirectly helps to control pronation (eversion) of
the rearfoot.
➢During the swing phase: the pretibial muscles actively dorsiflex the
ankle and extend the toes to ensure that the foot clears the ground.
• The eversion and/or abduction influence of the extensor digitorum
longus and fibularis tertius counterbalance the inversion and adduction
influence of the tibialis anterior.

44. • The fibularis longus and the fibularis brevis muscles (formerly called the
peroneus longus and peroneus brevis
• The fibularis longus and brevis have moment arms for eversion across the subtalar joint.
The lateral malleolus, serving as a fixed pulley, routes the fibular tendons posterior to
the axis of rotation at the talocrural joint. Both muscles are also plantar flexors of the
talocrural joint.
• The distal attachment of the fibularis longus generates forefoot eversion torque. This is
the base of the first ray everts and depresses (plantar flexes) slightly during maximal-
effort pronation of the unloaded foot. In addition, the fibularis longus stabilizes the first
tarsometatarsal joint against the potent medial pull of the tibialis anterior
• The fibularis longus and brevis are active throughout much of the stance phase of
walking.
➢Although relatively small, the concentric activation of the fibularis longus at and
immediately following heel contact may help control the kinematics of the pronating
rearfoot, which are being simultaneously further controlled by the eccentric activation
of the tibialis posterior and tibialis anterior.
➢The fibularis muscles are at their highest level of activation throughout mid stance and
push off, a time when the subtalar joint is supinating (inverting) and the dorsiflexing
talocrural joint is changing its direction of movement towards plantar flexion

46. • The tibialis posterior, flexor hallucis longus, and flexor digitorum longus are the
primary supinators of the foot.
• The tibialis posterior likely produces the greatest supination torque (especially in the
direction of adduction) across the subtalar and transverse tarsal joints
Activation of the Plantar Flexor and Supinator Muscles during Walking.
• From foot flat to just before heel off, the plantar flexors (most exclusively the soleus) act
eccentrically to decelerate the forward rotation (dorsiflexion) of the leg over the fixed
talus. Between the heel off and toe off phases, the muscles switch to a concentric
activation to assist with the necessary thrust for push off and early swing phase.
• Flexor hallucis longus, flexor digitorum longus, and intrinsic foot muscles (lumbricals
and interossei) hold the plantar surface of the extending toes firmly against the ground.
This action expands the weight-bearing surfaces of the toes
• Tibialis posterior, flexor hallucis longus, and flexor digitorum longus muscles resisting
pronation and assisting with supination during the stance phase of walking
• As the foot contacts the ground, tibialis posterior decelerates the pronating rearfoot,
which assists with a gradual and controlled lowering of medial longitudinal arch
• Throughout mid to late stance, contraction of the tibialis posterior helps guide the
rearfoot toward supination, reestablishing the height of the medial longitudinal arch.

47. Plantar Flexion Torque Generated for Propulsion.
• Posterior compartment muscles and fibularis longus and brevis (lateral compartment) contract
to plantar flex the talocrural joint. The amount of muscular activity produced by the plantar
flexor muscles during push off depends on the speed and vigor of walking.
• Maximal isometric plantar flexion torque exceeds the torque potential of all other movements
about the ankle and foot combined. a large amount of plantar flexion torque is needed to
rapidly accelerate the body up and forward during running, jumping, and climbing.
• Isolated plantar flexion torque is greatest when the ankle fully dorsiflexed (when muscles are
elongated) and is least when the ankle is fully plantar flexed
• The ankle is typically dorsiflexed as one prepares to sprint or jump, as the ankle vigorously
plantar flexes at the “take off ” of a sprint or jump, the contracting gastrocnemius is
simultaneously elongated by the action of the quadriceps extending the knee. This biarticular
arrangement prevents the gastrocnemius from over-shortening, allowing greater plantar
flexion torques to be generated throughout a larger range of ankle motion. Because the soleus
muscle does not cross the knee, its length-tension relationship is relatively unaffected by the
position of the knee.
• slow-twitch muscle characteristics of the soleus are optimally suited to control the subtle
postural sway movements of the leg (and body) over the talus during standing. The faster
twitch characteristics of the gastrocnemius, on the other hand, may be better suited for
providing a propulsive plantar flexion torque for activities that also involve dynamic knee
extension, such as jumping and sprinting
• the gastrocnemius and soleus are the strongest, producing about 80% of the total plantar
flexion torque at the ankle

51. Intrinsic muscles
• The actions of the intrinsic muscles assume the foot is unloaded
and the toes are free to move are not functionally. The intrinsic
muscles of the foot for assisting with the integrity of the medial
longitudinal arch and to help maintain standing balance.
• The intrinsic muscles provide dynamic stability to the foot and the
arch during the push off phase of walking. These functions explain
why most of the intrinsic muscles are maximally active during late
stance, just as the heel is rising off the floor.