1. Structure and Function of the Ankle and Foot
Chapter 11
Structure and Function of the Ankle and Foot
Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

2. Ankle and Foot Terminology
Plantar aspect of foot refers to sole or bottom of foot
Dorsal aspect refers to top or superior portion of foot
Rearfoot, midfoot, and forefoot are commonly used clinical terms that indicate specific areas of feet
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Overview of Gait Cycle
Gait cycle describes events that occur (while walking) within two successive heel contacts of same leg
Each gait cycle is divided into a stance phase (events that occur when foot is in contact with ground) and a swing phase (events that occur when foot is swinging through air)
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4. Swing Phase and Stance Phase
Stance phase elements
(1) heel contact; (2) foot flat; (3) mid stance; (4) heel off; (5) toe off
Swing phase elements
(1) early swing; (2) mid swing; (3) late swing
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5. Osteology: Distal Tibia and Fibula
Medial malleolus
Medial projection of bone from the distal tibia
Lateral malleolus
Projects laterally from distal fibula
Both malleoli serve as proximal attachments for collateral ligaments of ankle
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6. Osteology: Distal Tibia and Fibula – cont’d
Fibular notch
Concave portion of distal tibia that articulates with fibula, forming distal tibiofibular joint
Distal tibiofibular joint
Firm articulation allows little gliding between tibia and fibula
Serves as stable socket that accepts superior portion of
talus—forming talocrural (ankle) joint
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Osteology: Foot Bones
Three sets of bones
Tarsals
Metatarsals
Phalanges
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Tarsal Bones
Tarsal bones include:
Talus, calcaneus, navicular, cuboid
Medial, intermediate, and lateral cuneiforms
Three cuneiforms form transverse arch of foot
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Rearfoot
Talus
Trochlea: dome-shaped superior portion
Three facets on plantar aspect for articulation with calcaneus
Head: articulates with navicular
Calcaneus
Calcaneal tuberosity: attachment of Achilles tendon
Three facets on superior aspect for articulation with talus
Sustentaculum talus: medial projection of bone that serves as shelf to support talus
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Midfoot
Navicular
Navicular tuberosity: prominent medial projection of bone; site of distal attachment for spring ligament and tibialis posterior muscle
Cuneiforms
Forms medial half of transverse arch of foot
Cuboid
Forms lateral half of transverse arch of foot
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Forefoot
Metatarsals—all 5 consist of:
Concave base (proximal aspect)
Shaft
Convex head (distal aspect)
 Phalanges—all 14 consist of:
Concave base
Convex head
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12. Kinematics of Ankle and Foot
Fundamental movements occur within a plane perpendicular to three classic axes of rotation: medial-lateral, anterior-posterior, and vertical
Many joints produce an oblique movement best described with the applied terms of pronation or supination
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13. Fundamental Movements: Dorsiflexion and Plantar Flexion
Dorsiflexion and plantar flexion occur in sagittal plane about a medial-lateral axis of rotation
Dorsiflexion describes bringing dorsal part (top) of foot toward anterior aspect of tibia
Plantar flexion describes moving dorsal part of foot away from anterior aspect of tibia
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14. Fundamental Movements: Inversion and Eversion
Inversion and eversion occur in frontal plane about an anterior-posterior axis of rotation
Inversion turns a point anywhere on plantar aspect of foot toward midline
Eversion turns a point on plantar aspect of foot laterally, or away from, midline
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15. Fundamental Movements: Abduction and Adduction
These motions occur in horizontal plane about a vertical axis of rotation
Adduction describes horizontal plane rotation of foot that moves toward midline
Abduction describes horizontal plane rotation of foot that rotates away from midline
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16. Fundamental Movements: Pronation and Supination
Pronation is a combined movement of eversion, abduction, and dorsiflexion of any region of ankle and foot
Supination is a combined movement of inversion, adduction, and plantar flexion of any region of ankle and foot
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17. Proximal Joints: Talocrural Joint
Ankle joint, created by the articulation between trochlea (dome) of talus and concavity formed by distal tibia and fibula
This concave part of joint is often referred to as “mortise” because of its resemblance to a mortise joint used by carpenters
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18. Kinematics: Talocrural Joint
One degree of freedom permitting ankle dorsiflexion plantar flexion, sagittal plane motions important to walking and squatting
Muscles coursing anterior to medial-lateral axis of rotation perform dorsiflexion; muscles that course posterior perform plantar flexion
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19. Arthrokinematics: Talocrural Joint
With foot free, an open-chain dorsiflexion and plantar flexion occur as convex trochlea rolls and slides in opposite directions within concave mortise
With foot fixed, concavity formed by mortise rolls and slides in same direction over convex dome of talus
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20. Supporting Structures: Talocrural Joint
Interosseous membrane
Binds tibia to fibula
Provides stability to distal tibiofibular and talocrural joints
Anterior and posterior tibiofibial ligaments
Bind distal tibiofibular joint, improving stability of the mortise
Deltoid ligament
Limits eversion
Lateral collateral ligament
Limits inversion
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21. Functional Considerations: Positions of Talocrural Joint
Ankle is most stable during maximal dorsiflexion when most collateral ligaments and all plantar flexor muscles are stretched
Least stable position of talocrural joint is full plantar flexion when most collateral ligaments and all plantar flexor muscles are slackened
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22. Proximal Joints: Subtalar Joint
Articulation between facets on inferior surface of talus and matching facets on superior surface of calcaneus
Designed to allow frontal and horizontal plane motions between foot and lower leg, motions essential for adapting to uneven ground surfaces or “cutting” laterally or medially
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23. Kinematics: Subtalar Joint
Allow combined motions of inversion/adduction and eversion/abduction of foot
Side-to-side motions are inversion and eversion
Rotary (horizontal plane) motions are adduction and abduction
During all subtalar motions, trochlea is normally well stabilized within mortis shape of talocrural joint
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24. Functional Considerations: Subtalar Joint
Motion at subtalar joint allows independent movement between calcaneus and talus, a path that cuts through both frontal and horizontal planes
While walking, this motion occurs either when calcaneus is free, or held fixed under body’s weight
While in stance phase of walking, leg and talus move “as one” over fixed calcaneus
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25. Transverse Tarsal Joint Features
Consists of talonavicular joint and calcaneocuboid joint
Allows midfoot to move independently of rearfoot
Permits most pure form of pronation and supination: pronation has nearly equal elements of eversion, abduction, and dorsiflexion; supination has nearly equal elements of inversion, adduction, and plantar flexion
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26. Medial Longitudinal Arch of Foot
Load-bearing and shock absorbing foot structure
Active muscle forces are generally not required to support arch while standing (an exception being someone with pes planus)
Arch normally lowers, and rearfoot everts slightly to maintain forces at tolerable levels
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27. Medial Longitudinal Arch: Primary Passive Supporting Structures
Plantar fascia
Spring ligament
Many plantar ligaments
Integrity of talonavicular joint
Deltoid ligament
Shapes of tarsal bones
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28. Medial Longitudinal Arch: Primary Active Supporting Structures
Tibialis posterior
Peroneus longus
Intrinsic muscles of plantar aspect of foot
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Distal Joints of Foot
Include tarsometatarsal, metatarsophalangeal, and interphalangeal joints
All three of these joints play an important role in walking
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30. Distal Joints: Tarsometatarsal Joints
Articulation of metatarsal bases with distal surfaces of three cuneiforms and cuboid
Serve as base joints for rays of foot
Relatively rigid, except for first, allowing dorsiflexion and plantar flexion, coupled with inversion and eversion
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31. Distal Joints: Metatarsophalangeal Joints
Formed between convex head of metatarsals and shallow concavity of proximal phalanges
Allow similar motions to analogous metacarpophalangeal joints in hand: extension (dorsiflexion), flexion (plantar flexion), and abduction and adduction
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32. Distal Joints: Interphalangeal Joints
Each toe has a proximal and distal interphalangeal joint, except great toe with only one interphalangeal joint
Motion is limited primarily to flexion and extension
Extension is typically limited to 0-degree or neutral position of joint
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33. Muscle and Joint Interaction
Intrinsic muscles have both proximal and distal attachments within foot
Extrinsic muscles have proximal attachments within lower leg or distal femur, and distal attachments within foot
Muscles provide static control, dynamic thrust, and shock absorption to distal lower extremity
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34. Innervation to Extrinsic Muscles of Ankle and Foot
Extrinsic muscles of foot are arranged into anterior, lateral, and posterior compartments
Each compartment is innervated by tibial or common peroneal nerve, arising from sciatic nerve
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35. Innervation to Extrinsic Muscles of Ankle and Foot – cont’d
Tibial nerve continues distally through lower leg
Common peroneal nerve courses laterally, wraps around fibular head, and splits into superficial peroneal and deep peroneal nerves
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36. Innervation to Intrinsic Muscles of Foot
Tibial nerve bifurcates into medial and lateral plantar nerves
These nerves innervate all intrinsic muscles of foot, except for extensor digitorum brevis (innervated by deep branch of peroneal nerve)
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37. Anterior Compartment Muscles
Tibialis anterior, extensor digitorum longus, extensor hallucis longus, and peroneus tertius
Originate on anterior and lateral aspects of proximal tibia, adjacent fibula, and interosseous membrane
All four muscles are innervated by deep peroneal nerve and perform dorsiflexion as one of their primary actions
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38. Functional Considerations: Foot Drop
Foot “drops” into plantar flexion as leg is advanced during swing phase of gait
In order to prevent foot from dragging, often a “high-stepping” gait is performed that appears like stepping over an imaginary obstacle  
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39. Functional Considerations: Foot Slap
If dorsiflexors are unable to generate sufficient eccentric activation between heel contact and foot flat, forefoot quickly drops to ground
Referred to as foot slap due to sound that occurs as sole of foot hits floor
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Shin Splints
Condition that may affect muscles attached to medial and posterior sides of tibia
Often involves dorsiflexor muscles
If dorsiflexors are untrained or mechanics of foot and ankle are faulty, these muscles may become inflamed through overuse
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Shin Splints – cont’d
Excessive pronation of foot during running or walking often exacerbates or contributes to shin splints
For this reason, clinicians often recommend orthotics to help support foot and provide inflamed dorsiflexor muscles much relief
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42. Lateral Compartment Muscles: Peroneus Longus
Proximal attachment
Lateral condyle of tibia; head and proximal 2/3 of lateral surface of fibula
Distal attachment
Lateral surface of medial cuneiform and base of first metatarsal
Actions
Eversion
Plantar flexion
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43. Lateral Compartment Muscles: Peroneus Brevis
Proximal attachment
Distal 2/3 of lateral surface of fibula
Distal attachment
Styloid process of the fifth metatarsal
 Actions
Plantar flexion
Eversion
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44. Functional Considerations: Lateral Compartment Muscles
Provide an important element of muscular stability to lateral aspect of ankle and foot
With weakness of peroneal muscles, foot is more likely to “flip” strongly into inversion, possibly resulting in lateral ankle sprain
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45. Posterior Compartment Muscles
Superficial group
Gastrocnemius, soleus, and plantaris
Deep group
Tibialis posterior, flexor digitorum longus, and flexor hallucis longus
All muscles are innervated by tibial nerve and perform a combination of plantar flexion and inversion (supination)
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46. Functional Considerations: Soleus versus Gastrocnemius
Soleus is composed of primarily slow-twitch muscle fibers best equipped for standing or controlling “postural sway”
Gastrocnemius, on the other hand, is composed of more fast-twitch fibers best equipped for sprinting and jumping  
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47. Functional Considerations: Raising Up on Tiptoes
Ease of standing up on tiptoes is largely due to mechanical advantage of plantar flexors during this action
Plantar flexors function as a second-class lever system, providing a mechanical system that favors strength over speed and range of motion
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48. Functional Considerations: Supporting Medial Longitudinal Arch
Non-contractile supporting structures of medial longitudinal arch may overstretch, leading to excessive pronation
In response, deep group muscles of posterior compartment help support medial longitudinal arch
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49. Intrinsic Foot Muscles
Intrinsic muscles that originate and insert within foot are largely responsible for actions of toes
As a group these muscles stabilize foot during push-off phase of walking or running
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Dorsum of Foot
Extensor digitorum brevis
Proximal attachment dorsal-lateral aspect of calcaneus, just proximal to calcaneocuboid joint
Distal attachment
Through four separate tendons that blend with extrinsic extensor tendons coursing to digits 1-4
Actions
Extension of first four toes
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Plantar Aspect of Foot
First layer
Flexor digitorum brevis, abductor hallucis, and abductor digiti minimi
Second layer
Quadratus plantae and four lumbricals
Third layer
Adductor hallucis, flexor hallucis brevis, and flexor digiti minimi
Fourth layer
Dorsal and plantar interossei
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Summary
Structure of ankle and foot designed to absorb impact of weight bearing and adapt to shape of ground
Dysfunctions of hip, knee, or even back may be associated with problems originating at ankle or foot
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