ankle and foot

Ankle

kinematics
Range of motion

·      uniplanar hinge joint

·      transverse axis that slopes downwards and laterally

·      from medial talus in concavity of articular comma

·      to lateral talus at apex of articular triangle

·      range of motion is 45o total

·      30o dorsiflexion

·      45o plantarflexion

·      associated with rotation of talus

·      plantarflexion causes 4-8o IR of talus

·      due to tethering of medial talus by deltoid

Surface joint motion

·      instant centre of motion falls within talus

Stability

·      provided by

·      shape of mortise (maximal in dorsiflexion)

·      interosseous membrane

·      reinforced by

·      talofibular and calcaneofibular ligaments laterally

·      deltoid ligament medially

kinetics

·      forces acting on ankle joint are 4 times body weight at preswing

·      fibulotalar joint transmits 1/6 of force through leg

Kinematics

·      small anatomic deviations in tibiotalar and fibulotalar joint result in siginficant changes in stresses on talus

Foot

kinematics
Tarsal bones

Subtalar joint

·      axis extends forwards and

·      upwards 40o

·      medially 20o

·      ROM is

·      inversion 20o

·      eversion 5o

·      functional ROM during gait is 8o total

·      effect of oblique axis of subtalar joint is opposite movement in other members of joint

·      if foot fixed, inversion causes external rotation of tibia (and vv)

·      if foot free, inversion causes adduction of forefoot (and vv)

Midtarsal joint

·      consists of TN and CC joints

·      two types of motion

·      rotation

·      flexion-extension

·      axes of two joints vary with subtalar joint position

·      parallel when subtalar joint in eversion

·      become divergent with inversion of subtalar joint

·      result is increased stability in inversion

·      occurs during last half of stance phase

Midfoot

·      intertarsal and tarsometatarsal joints

·      total motion is

·      few degrees dorsiflexion

·      15o plantarflexion

·      2nd MT base recessed into midfoot

·      makes 2nd ray more stable than 1st ray

Metatarsal break

·      axis through which toes extend through MTP jt

·      is usually 60o from long axis of foot

·      important in gait

·      reinforces external rotation of tibia during second half of stance phase

·      increases inversion of forefoot and stabilises longitudinal arch

Plantar fascia

·      acts as tether between bony structures of foot

·      passively locks tarsal joints for stability during gait

·      windlass mechanism

·      tightens and elevates longitudinal arch when MTP jts extended

kinetics
Stance

·      all metatarsal heads in contact with floor during stance

·      transverse metatarsal arch does not exist

·      load borne by

·      heel 50%

·      metatarsal heads 50%

·      of metatarsal heads

·      of hallux takes 60%

·      of lesser toe takes 10% each

Gait

·      ground reaction force

·      starts slightly medial in heel

·      progresses rapidly along medial border of foot

·      passes through 2nd MT head

·      then enters hallux for toe-off

·      2nd MT head concentrates ground reaction force

·      longer

·      more stiff