The term ankle refers to the talocrural joint, a composite joint formed between the shin bone (tibia), fibula (calf bone), and talus (upper part of the foot), the main bones of the lower extremity. The term foot, on the other hand, is used to refer to all the tarsal bones that make up the structure of the foot and the various joints located on the distal side of the ankle joint.
The foot is anatomically divided into three main areas, each of which consists of a series of bones with unique functions and one or more specialised joints. The rearfoot (hindfoot) is made up of the coccyx, heel bone, and the subtalar joint between them, which is an important weight-bearing structure.
The midfoot is made up of the remaining ankle bones that form the arch of the foot, including the transverse and distal intertalar joints, which are responsible for the flexibility of the foot. The forefoot is made up of the hip and toe bones that provide propulsion during walking, and includes the ankle-foot-hip joint and all joints distal to it.
In anatomical terms, the expressions anterior and posterior are used as general terms to describe the position of the shin bone and the tibia (i.e. calf). However, when describing the ankle and foot structures, the terms distal and proximal are often used interchangeably to describe their positioning.
When referring to the surface of the foot, the terms dorsal and plantar are technical terms used to describe the upper and lower surfaces of the foot, respectively. When comparing the upper and lower extremities of the human body, there are a number of osteological similarities between the distal calf and the distal lower arm, and the ankle and foot in particular share many structural similarities with the wrist and hand.
The radius in the lower arm of the upper extremity and the tibia in the calf of the lower extremity form a complex joint with a series of smaller bones, such as the carpal and ankle bones, respectively. The carpal and ankle bones are remarkably symmetrical, with exactly seven bones each, especially when the carpus of the wrist is categorised as a seed bone rather than a separate carpal bone.
The toe bones and the bones at the end of the foot have very similar planes of motion to the finger bones and the bones of the hand. A notable difference is that the first (big) toe of the foot has relatively limited functional development compared to the thumb of the hand.
During fetal development, the entire lower limb progressively turns inwards, and as a result of this developmental process, the big toe is positioned on the medial surface of the foot, while the top of the foot naturally faces dorsally. This anatomical orientation is very similar to the hand orientation observed when the lower arm is completely prone.
The plantigrade position of the foot, which is critical to human bipedalism, is an essential structure for efficient walking and maintaining a stable upright posture. This is in the same vein as the flexion and extension of the wrist observed during the lower arm prone position is very similar to the plantarflexion and dorsiflexion of the ankle.