Ankle Anatomy and Fractures

Ankle Joint

  • Formed by:
    • Distal tibia
    • Distal fibula
    • Talus
  • Articulations:
    • Tibia & fibula
    • Tibia & talus
    • Fibula & talus
  • Talocrural joint (Mortise joint)
  • Tibial plafond

Joints

  • Talocrural joint
    • Articulation of distal tibia, distal fibula, and talus
    • Synovial hinge joint - dorsiflexion & plantarflexion
  • Distal tibiofibular joint
    • Articulation of the distal fibula with the fibular notch of the distal tibia
    • Syndesmosis - the tibia and fibula are joined by:
      • The interosseous membrane
      • Anterior and posterior tibiofibular ligaments
      • Inferior transverse tibiofibular ligament

Bony Ring

  • The ankle & tibia/fibula form a bony ring
  • Ring structure of 3 bones – the tibia, talus & fibula
  • Linked by the medial and lateral collateral ligaments and the interosseous membrane.

Muscles of the Ankle & Lower Leg

  • Anterior group
    • Extensor group
    • Peroneus group
  • Posterior group
    • Superficial muscle layers
    • Deep muscle layers

Muscles – Anterior Group

  • Extensor group
    • Tibialis anterior: Lateral tibia to Medial cuneiform & 1st M/T
    • Extensor digitorum longus: Proximal fibula to 2nd to 5th toes
    • Extensor hallucis longus: Anterior fibula & interosseous membrane to Distal phalanx hallux
  • Peroneus Group
    • Peroneus longus: Proximal tibia & fibula to 1st M/T & medial cuneiform
    • Peroneus brevis: Lateral surface of distal fibula to 5th M/T

Muscles – Posterior Group

  • Superficial layer
    • Gastrocnemius: Distal femur to Achilles tendon
    • Soleus: Proximal tibia & fibula to Achilles tendon
    • Plantaris: Distal femur to Achilles tendon and calcaneus
  • Deep layer
    • Tibialis posterior: Posterior proximal tibia to Navicular & medial cuneiform
    • Flexor hallucis longus: Posterior proximal fibula to Distal phalanx hallux
    • Flexor digitorum longus: Proximal tibia to Distal phalanges 2nd to 5th toes

Ligaments

  • Medial Ligament
    • Attached to the medial malleolus
    • Four ligaments:
      • Talus – tibio-talar ligament
      • Calcaneus – tibio-calcaneal ligament
      • Navicular – tibio-navicular ligament
      • Spring ligament – tibio-spring ligament
    • Resists over-eversion of the foot.
  • Lateral Ligament
    • Originates from the lateral malleolus
    • Three ligaments:
      • Anterior talofibular: lateral malleolus and lateral aspect of the talus.
      • Posterior talofibular: lateral malleolus and the posterior aspect of the talus.
      • Calcaneofibular: lateral malleolus and the calcaneus.
    • Resists over-inversion of the foot.

Arterial Supply

  • Anterior tibial artery
    • Arises from popliteal artery at the level of the fibular head
    • Becomes dorsalis pedis artery
  • Posterior tibial artery
    • Arises from popliteal artery at the level of the fibular head
    • Divides into the medial and lateral plantar arteries in the foot
  • Peroneal artery
    • Arises from the posterior tibial artery ~2cm distal to the proximal fibula

Venous Drainage

  • Deep Veins
    • Great saphenous: Drains into the femoral vein.
    • Small saphenous: Drains into the popliteal vein.
  • Superficial Veins
    • Anterior tibial vein: Follows the path of the associated artery
    • Posterior tibial vein: Follows the path of the associated artery
    • Both veins merge to form the popliteal vein posterior to the knee

Mortise Projection

  • Joint space should be uniform
  • Talar dome smooth, with no irregularities
  • Gap between tibia and fibula should not exceed 6mm when measured 1cm proximal to the tibial plafond

Lateral Projection

  • Check the base of the 5th M/T
  • Check the calcaneus
  • Check the neck of the talus

Bohler’s Angle

  • Normal angle: 30o30^{o}
  • Shallower angle raises suspicion of a calcaneal fracture

The Tear-Drop Sign

  • Tear-shaped opacity anterior to talotibial joint on a lateral
  • Indicates Ankle joint effusion (excess fluid in the synovial space)
  • Common causes:
    • Haemorrhage (trauma)
    • RA
    • Septic Arthritis
    • Synovitis

Pilon Fracture

  • Intra-articular # fracture of the distal tibia.
  • High energy injury
  • Axial loading drives the talus into the tibial plafond

Weber Ankle Fracture Classification

  • Based on fracture position relative to the distal tibio-fibular syndesmosis.
  • Weber A: # distal to syndesmosis, syndesmosis intact, usually stable.
  • Weber B: Distal extent of # at the level of the syndesmosis, Syndesmosis usually intact, variable stability.
  • Weber C: # proximal to syndesmosis, disruption of syndesmosis, unstable.

Maisonneuve Fracture

  • Fracture of proximal fibula (spiral) and disruption of the tibiofibular syndesmosis
  • Suspect if:
    • Isolated # of the medial malleolus with widening of the medial joint space
    • Weber Type C
  • Unstable