Ankle and Subtalar Joint Mechanics

Ankle: Talocrural Joint

• One degree of freedom
• Axis of rotation is oblique, through the body of the talus and the tips of both malleoli
• Frontal plane: deviated 10 degrees from the ML axis
• Horizontal plane: deviated 6 degrees from the ML axis
• Dorsiflexion: associated with slight abduction and eversion (pronation)
• Plantarflexion: associated with slight adduction and inversion (supination)
• Normal ROM: Dorsiflexion (15-25 degrees), Plantarflexion (40-55 degrees)
• Functional ROM: Gait (10 degrees DF, 20 degrees PF), Running (20 degrees DF, 30 degrees PF), Stair Descent (21-36 degrees DF)
• During OKC (unloaded) dorsiflexion:
  • Convex talar dome rolls anteriorly, slides posteriorly
  • Deltoid ligament (tibiotalar fibers), calcaneofibular ligament, posterior talofibular ligament tense during dorsiflexion

Subtalar Joint

• Pronation (unlocking of the foot)
  • Calcaneal eversion (valgus)
  • Talar adduction (internal rotation of talus, coupled with internal rotation of tibia and fibula)
  • Talar plantarflexion: anterior/inferior translation, lowering of the MLA
• Supination
  • Calcaneal inversion
  • Talar abduction
  • Talar dorsiflexion
  • Tibiofibular external rotation
• Normal ROM: 20 degrees inversion, 10 degrees eversion
• Functional ROM: 4-6 degrees inversion and eversion during normal gait
• In OKC (non-weight bearing) supination:
  • Calcaneal inversion, calcaneal adduction, calcaneal plantarflexion
• In OKC pronation:
  • Calcaneal eversion, calcaneal abduction, calcaneal dorsiflexion
• In WB (weight bearing) supination:
  • Calcaneal inversion, talar abduction, talar dorsiflexion, tibiofibular external rotation
• In WB pronation:
  • Calcaneal eversion, talar adduction, talar plantarflexion, tibiofibular internal rotation
• In WB, talar movement is opposite to calcaneal movement in NWB
• In the posterior articulation of the subtalar joint:
  • Talar plantarflexion (posterior facet): concave
  • Calcaneal plantarflexion: convex
• During calcaneal inversion:
  • Calcaneus rolls medially
  • Calcaneus slides laterally
• During calcaneal eversion:
  • Calcaneus rolls laterally
  • Calcaneus slides medially
• During talar abduction and dorsiflexion (CKC supination):
  • Talus slides superiorly and laterally on calcaneus
• During talar adduction and plantarflexion (CKC pronation):
  • Talus slides inferiorly and medially on calcaneus

Transverse Tarsal Joint (TTJ)

• AKA midtarsal joint
• Acts as the transitional link between rearfoot and forefoot
• Mechanically linked to the subtalar joint
• Controls most of supination and pronation
• Allows the foot to adapt to uneven surfaces during weight-bearing activities
• Two axes of rotation: longitudinal and oblique
• Supination/pronation ROM: about 2:1 ratio
• Most weight-bearing activities involve a blending of movements across both axes
• Longitudinal axis: almost straight anteroposterior axis of rotation
• Oblique axis: strong vertical and medial-lateral pitch

Talonavicular Joint (TNJ)

• Resembles a ball-and-socket joint
• Provides substantial mobility to the medial column of the foot
• Spring ligament supports the talar "acetabulum", the talonavicular joint and the medial longitudinal arch

Calcaneocuboid Joint (CCJ)

• Resembles a saddle joint
• Allows less motion compared to the TNJ
• Provides stability to the lateral column of the foot
• Lateral fibers of the bifurcate ligament form the primary bond between calcaneus and cuboid
• Stabilized by the long plantar ligament and short plantar ligament (important for the lateral longitudinal arch)

Combined Action of STJ and TTJ (OKC)

• Active supination of an unloaded foot
  • Supination at both TTJ and STJ
  • Tibialis posterior muscle: prime supinator of the foot
  • TTJ: relatively rigid calcaneocuboid joint acts as a pivot point for the talonavicular joint
  • Tibialis posterior contributes to the navicular spin and raising of the medial longitudinal arch
  • TNJ: Concave navicular and spring ligament spin around the convex talar head
• Active pronation of an unloaded foot
  • Pronation at both TTJ and STJ
  • Fibularis longus: lowers the medial side and raises the lateral side of the foot
  • TNJ: Concave navicular and spring ligament spin in the opposite direction (compared to supination) around the convex talar head

Medial Longitudinal Arch (MLA) of the Foot

• Primary load-bearing and shock-absorbing structure
• Formed by calcaneus, talus, navicular, cuneiforms, and three medial metatarsals
• Keystone: talonavicular joint
• Plantar fascia acts like a semi-elastic tie-rod
• Responds to larger and more dynamic loads

Combined Action of STJ & TTJ (CKC): Osteokinematics during Early to Mid Stance Phase

• STJ pronation and lowering of the MLA: coupled with internal rotation of the leg, allows the foot to function as a shock absorber and produces a pliable midfoot.
• TTJ relative supination: acts as a counterforce from the ground and allows full STJ pronation.
• STJ pronation helps to lower the MLA and internally rotate the leg, which allows for shock absorption and a flexible midfoot.
• Relative supination at the TTJ allows the STJ to fully pronate while still maintaining contact with the ground.

Combined Action of STJ & TTJ (CKC): Osteokinematics during Mid to Late Stance Phase

• STJ supination and raising of the MLA: coupled with external rotation of the leg, converts the midfoot to a rigid lever for push off.
• TTJ relative pronation: allows the midfoot and forefoot to maintain firm contact with the ground during push off.

Distal Intertarsal Joints

• Three joints or joint complexes in the midfoot:
  • Cuneonavicular joint
  • Cuboideonavicular joint
  • Intercuneiform and cuneocuboid joint complex
• Functions:
  • Assist the TTJ in pronating and supinating the midfoot
  • Provide stability across the midfoot by forming the transverse arch (keystone: intermediate cuneiform)

Tarsometatarsal Joints and Intermetatarsal Joints

• Least mobility at the 2nd and 3rd tarsometatarsal joints for longitudinal stability (useful in late stance)
• 1st tarsometatarsal joint:
  • Plantarflexion with slight eversion
  • Dorsiflexion with slight inversion (These movement combinations are atypical for the foot)

This quiz covers the anatomy and biomechanics of the talocrural and subtalar joints. It includes details on their range of motion, functional implications for activities like walking and running, and ligament involvement during dorsiflexion. Perfect for students studying kinesiology or physical therapy.