- 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.