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Role of the Ankle and Subtalar Joint in Gait


- See:
      - Ankle Joint: Anatomy
      - Equinus Contracture
      - Gait (discussion of)
      - Sub-Talar Joint

- Diagram:

- Ankle Joint: During Gait:
    - ankle joint has an oblique axis;
    - in frontal plane, ankle joint is angled 82 deg, directed laterally;
    - in transverse plane, axis is directly laterally & posteriorly about 20-30 deg;
    - as a consequence of this oblique ankle axis is that foot  externally rotates when the ankle is in maximal dorsiflexion;
          - when the foot plantar flexes, it internally rotates;
    - w/ foot fixed on ground as in stance phase of gait;
          - forward tibial progression (ankle dorsiflexion) results in tibial internal rotation;
          - when tibia is behind foot (ankle plantar flexion), it is externally rotated;

- Subtalar Joint During Gait:
    - external rotation of leg produces supination of the foot;
        - during wt bearing, external rotation of limb & subsequent forefoot supination are followed by pronation twist of forefoot to remain plantigrade;
        - this tends to lock the foot, making it a rigid lever;
    - internal rotation of the leg produces a pronated foot;
        - internal rotation of leg & its subsequent pronation are followed by supinatory twist of the forefoot to remain plantigrade;
        - this mechanism unlocks midtarsal joint & produces mobile midfoot noted at time of heel contact & first 15% of the gait cycle;
    - inversion of the heel in the normal foot promptly occurs as wt is transferred from heel to forefoot when a person rises on the toes;
         - such inversion of the heel causes the mid foot to covert from a mobile structure to a rigid lever;
    - when the heel is elevated during standing or at the time of push off, wt of the body is shared by all the metatarsal heads;
          - to achieve this fair division of the body wt among the metatarsals, foot must supinate slightly and deviate laterally;

- Ankle Joint and Subtalar Joint Work Together:
    - ankle combines dorsiflexion with abduction and plantar flexion w/ adduction, subtalar joint combines dorsiflexion, abduction, & eversion in one direction and plantar flexion, adduction, and inversion in the other direction;
         - these combined subtalar motions are referred to as pronation & supination;
    - when the subtalar joint is fused, rotation is increased in the ankle and may cause arthritic change;
         - when the ankle is fused, greater stresses are placed on the sub-talar and midtarsal joints;
    - dorsiflexion of the toes tightends the plantar aponeurosis and assists in inversion of the heel;
         - supinatory twist activates the locking mechanism in foot, thus converting a flexible foot into a rigid lever, an action that is necessary at push off



Ankle and subtalar kinematics measured with intracortical pins during the stance phase of walking.

The jargon of pedal movements.