The function of all of the muscles in the lower limb originating below the knee is to move the foot. These muscles insert on any one or several of the 26 bones of the foot.
Bones of the Foot
The 26 bones of the foot, separated into the three main sections of the foot: Forefoot, Midfoot, Hindfoot, is summarized below:
Joints of the Foot
The forefoot consists of five metatarsals starting with the first to the fifth; and five toes, each of which consists of three bones (except for the big toe which consists of two). The bones of each toe are the proximal phalanx, the middle phalanx, and the distal phalanx (except the big toe which has only proximal and distal). Between each of these bones is a joint which allows for the movement necessary of each section of the foot.
The joints of the forefoot are:
- MTP joint—metatarsal phalangeal joint - between the metatarsal and the proximal phalanx of the adjacent toe.
- PIP joint—proximal interphalangeal joint - between the proximal phalanx and the middle phalanx of each toe.
- DIP joint—distal interphalangeal joint - between the middle phalanx and the distal phalanx of each toe.
- The big (“great”) toe has only one joint between its two phalanges and therefore this joint is called the great (or “big” ) toe interphalangeal joint.
Metatarsal head is the end of the metatarsals, which articulate with the joints of the adjacent bones (generally used to describe the distal metatarsal head, the portion that articulates with the proximal phalanx of the adjacent toe.)
The Midfoot consists of five boneswith numerous articular surfaces (surfaces which articulate by way of joints with other bones).
- three cuneiform bones: medial, middle and lateral
Distally, the fourth and fifth metatarsals articulate with the cuboid bone. The first, second and third metatarsals articulate with each of their respective cuneiform bones. Each of these has an individual joint capsule but all are wrapped in one big capsule as well to form the tarso-metatarsal joint (the “Lis Franc joint”). Proximally, the talonavicular and calcaneocuboid joints, together form the combined articulations of the midtarsal joint (of “Chopart”).
The tibia articulates with the dome of the talus and thereby transmits the forces of the leg to the ankle. This is commonly called the “Tibialtalar joint” or simply the “Ankle joint”. In turn, the talus articulates with the calcaneus, the main weight-bearing (and the largest) bone of the foot by way of the subtalar joint. The subtalar joint, known as the “agility joint”, is a key joint in the ankle. It has three surfaces of articulation with three separate facet joints. A great deal of the movement in the ankle happens in this joint - the rest of the movement happens at the tibialtalar joint.
The plantar fasciais an important stabilizer in the foot where a great deal of foot pathology begins. The plantar fascia originates from the plantar surface of the calcaneus and attaches to the plantar surfaces of the five metatarsal heads and proximal phalanges of the toes. The plantar fascia acts as a major stabilizer of the foot (see diagram). It helps maintain the arch of the foot and is an anti-pronator. In its function of maintaining the congruity of the relationship between the calcaneus and the metatarsal heads, it resists the torsion movement of the forefoot in relation to the hindfoot during pronation. Most of the eversion of pronation occurs in the mid and forefoot while the calcaneus remains stable in the hindfoot.
The Achilles Tendon is one of the longest and strongest tendons in the body. It also has one of the lowest blood supplies of any tendon and therefore is prone to chronic injury. Once inflammation, or particularly a rupture, occurs it is difficult to repair given the low blood supply. The Achilles Tendon inserts on the calacaneus (posterior aspect) and is the main muscle which plantarflexes the foot and thereby allows for propulsion. It is also a major anti-pronator. Dorsiflextion is a significant component of pronation, and therefore the Achilles Tendon acts as an antagonist. It also causes inversion at the extreme.
The Achilles Tendon is formed in the middle third of the posterior aspect of the tibia. The two calf muscles join in the middle third of the tibia to form the Achilles Tendon.
- Gastrocnemius is a large muscle which originates on the posterior aspect of the femur.
- Soleus is a large muscle which originates on the posterior aspect of the upper third of the tibia.