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The Ankle Complex

Functions of the Ankle
Joint Structure of the Ankle
Kinematics of the Ankle
Muscles at the Ankle
Ankle Stability
Mechanism of Injury at the Ankle


ObjectivesĄG After studying this topic, the students will be able to

  1. to identify the structure of the ankle, including joint type, articular shape, and the surrounding tissues
  2. to describe joint motions occurring at the ankle, including osteokinematic and arthrokinematic movements, muscle actions, and factors checking ankle motions
  3. to understand joint stability mechanism resulting from bony and ligament constraints as well as the possible mechanisms of injury
  4. to distinguish characteristics of the weight-bearing joint from those of the non-weight-bearing joint

  1. Neumann DA (2002).  Ankle and foot.  In Neumann DA: Kinesiology of the Musculoskeletal System: Foundations for Physical Rehabilitation. Philadelphia: Mosby.  Chapter 14, pp. 477-521.
  2. Smith LK, Weiss EL, Don Lehmkuhl L (1996). Brunnstrom's Clinical Kinesiology, 5th ed.  Philadelphia, F.A. Davis.  Chapter 10, pp. 332-362.
  3. Sammaco GJ & Hockenbury RT (2001).  Biomechanics of the ankle and foot.  In Nordin M & Frankel VH: Basic Biomechanics of the Musculoskeletal System.  Philadelphia: Lippincott Williams & Wilkins. Chapter 9, pp.222-255.

Functions of the Ankle


  • To provide stability for weight bearing
  • To allow the mobility of the foot
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    Joint Structure of the Ankle Complex


    Joints at the ankle complex
  • talocrural joint (ankle joint)ĄG principal joint at the ankle complex
  • inferior tibiofibular jointĄG symdesmosis
  • subtalar jointĄG Most scholars treat the subtalar joint as part of the "foot complex". Will be discussed in the "Foot" page.
  • Ą@

    Talocrural joint

  • synonymĄG ankle joint
  • proximal componentĄG concave ankle mortise
  • concave distal tibia
  • concave distal fibula
  • distal componentĄG convex dome of the talus
  • joint typeĄG hinged joint
  • motionsĄG convex on concave
  • ankle dorsiflexion/ plantarflexion with posterior/ anterior glide of the talus on the ankle mortise
  • DOF = 1
  • resting positionĄG slight ankle plantarflexion (10º)
  • closed packed positionĄG full ankle dorsiflexion
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    Inferior tibiofibular joint

  • synonymĄG distal tibiofibular joint
  • proximal componentĄG concave facet of the distal tibia
  • distal componentĄG convex facet of the distal fibula
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    Kinematics of the Ankle


    Ankle dorsiflexion and plantarflexion

  • joint involved
  • talocrural joint
  • inferior tibiofibular joint
  • plane of motionĄG sagittal plane (actually triplane)
  • axis of rotation
  • a frontal axis passing through the center of the lateral malleolus of the fibular and the lower tip of the medial malleolus of the tibia
  • at an angle of 13-18º laterally from the frontal plane and an angle of 8-10º from the transverse plane
  • osteokinematic movements
  • range of motion (ROM)
  • 0-20º for ankle dorsiflexion
  • 0-55º for ankle plantarflexion
  • triplanar motionsĄG Since the joint axis of the ankle is not just in the cardinal plane, the motions occuring at the ankle joint present a triplanar motion pattern.
  • dorsiflexion with eversion and abduction
  • plantarflexion with inversion and adduciton
  • functional rangeĄG at least 10º of ankle dorsiflexion is necessary for normal gait
  • closed kinematic chain motions
  • deep squatting
  • stance phase of the gait cycle
  • arthrokinematic movements (convex on concave)
  • talocrural joint
  • posterior glide of the talus on the ankle mortise with ankle dorsiflexion
  • anterior glide of the talus on the ankle mortice with ankle plantarflexion
  • inferior tibiofibular joint
  • separation of the fibula from the tibia
  • superior glide of the fibula on the tibia with dorsiflexion
  • factors limiting ankle dorsiflexion
  • ankle mortise
  • passive tension of the Achilles tendon
  • factors limiting ankle plantarflexion
  • calcaneus
  • tension of the anterior component
    1. Feel the separation of the ankle mortise during ankle dorsiflexion.

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    Muscles at the Ankle


    Ankle dorsiflexors

  • tibialis anteriorĄG dorsiflexion + inversion
  • toe extensors
  • peroneus tertiusĄG dorsiflexion + eversion
  • Ankle plantarflexors

  • triceps suraeĄG two-joint muscle
  • medial head of the gastrocnemius
  • lateral head of the gastrocnemius
  • soleus
  • toe flexors or tibilais posterior
  • peroneus longusĄG plantarflexion + eversion
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    Ankle Stability


    Factors Affecting Ankle Stability

  • bony configurationĄG most important
  • shape of dome of the talusĄG
  • anterior edge > posterior edge
  • medial edge > lateral edge
  • tension of ligaments or other connective tissues
  • deltoid ligament (medial collateral ligament)ĄG prevent valgus stress
  • lateral collateral ligamentsĄG prevent varus stress
  • anterior talofibular ligamentĄG prevent a stress toward plantarflexion + inversion
  • calcaneofibular ligamentĄG prevent a stress toward pure inversion
  • posterior talofibular ligament
  • anterior inferior tibiofibular (AITF) ligamentĄG hold two bones together
  • muscular arrangement
  • peroneus longus and brevis
  • tibialis posterior
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    Mechanism of Injury at the Ankle


    Direct stress

  • ankle sprain
  • avulsion fracture of the medial malleolus
  • Ą@

    Repeated stresses

  • repeated ankle plantarflexion motion à Achilles tendon tendinitis à Achilles tendon rupture

  • repeated eccentric ankle dorsiflexion à  anterior compartment syndrome
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    Established on 11/25/2002 and Last Updated 03/25/2005 © 2004 Huei-Ming Chai, PhD PT          All Right Reserved