Anatomy

What structures are most commonly injured?

The foot has 26 bones, but it also has four layers of muscles and tendons, joints, veins, arteries, nerves and fatty tissue. It is very important to remember that a force severe enough to break a bone will damage some of these other tissues as well. Injury causes swelling and bleeding which eventually forms scar tissue. During the healing process, this scar tissue can bind together the muscles and tendons which normally glide over one another. How well the foot functions after a fracture depends on how well both bone and soft tissue heal.

The names of the bones going from the heel forwards are:

Calcaneus – Heel bone
Talus – Ankle Bone
Navicular
Medial, Intermediate (Middle) and Lateral Cuneiform
Cuboid
Metatarsals (Lesser Toes)
1st Metatarsal (Big Toe, Hallux)
1st Proximal Phalanx (Big Toe, Hallux)
1st Distal Phalanx (Big Toe, Hallux)
Proximal, Middle & Distal Phalanges (Lesser Toes)

The big toe is officially called the hallux. Many parts of the foot that are associated with the hallux include the word hallucis in the name. For example, the long muscle that flexes (bends) the big toe downwards is called flexor hallucis longus.

There are a large number of joints between the bones in the foot. The important ones are:

The ankle joint between the end of the shin and the talus (ankle bone). It allows up and down movement of the foot.

The subtalar joint between the talus and the calcaneus (heel bone). It allows side to side movement so that you can stand on the side of a sloping surface.

The transverse tarsal joint (also called Chopart’s joint) is formed by the talus and calcaneus on one side and the navicular and cuboid on the other. It allows some pivoting movements of the forefoot on the hindfoot and flattening of the arch.

The tarsometatarsal joint (also called Lisfranc’s joint) is between the distal tarsal bones, (the three cuneiforms and the cuboid) and the metatarsals. Its complex anatomy allows for a little movement of the longitudinal arch of the foot and a bit more movement at the outer border of the foot Dislocation of this joint is a serious injury often associated with fracture of the metatarsals and/or cuneiform bones.

Metatarsophalangeal (MTP) joints. There are five of these. These joints are between the heads of the metatarsals and the proximal phalanges. They allow flexion and extension of the toes. When you stand on tiptoe the MTP joints are extended and you are bearing weight on the toes and the joints.

Interphalangeal joints. These nine joints are located between the phalanges (toe bones) and allow the toes to curl. Loss of this function is not usually a severe handicap.

The big muscles that power walking by moving the ankle, foot and toes, are located in the leg. If you wiggle your toes and put your fingers on the muscle on the outer side of the front of the leg just below the knee, you can feel the muscles contracting. Their pull is transferred to the bones of the foot by long thin tendons that extend from the muscle in the leg, down across the ankle and into the foot to end in the toes. These tendons glide inside special tendon sheaths. These tendon sheaths may be damaged when the foot is injured.

Other intrinsic muscles of the foot form the flesh of the sole of the foot. There are actually four layers of muscles on the sole of the foot. They are important in maintaining the arch of the foot, a critical part of the shock absorption system. These muscles are protected from weight bearing by the plantar fascia, a tough layer of fibrous tissue next to the skin on the sole of the foot. Bleeding into the sole of the foot from a fracture may result in scar tissue which may bind all these layers together and interfere with function.

Viewed from the side there are other interesting aspects of foot anatomy. The heel pad is a specialized region situated between the heel bone and the skin. It has an elastic honeycomb-like structure with the "cells" filled with fatty tissue. These cells work like a shock absorber. When the heel comes down the cells stretch and flatten, absorbing some of the shock. An injury severe enough to break the calcaneus (heel bone) is also often severe enough to disrupt the heel pad. It may heal with solid scar replacing the specialized heel pad structure. This reduces its ability to absorb shock.

Further forward is the arch of the foot. This is a dynamic feature of the foot only partly due to the shape of the bones. When you are standing, the muscles that maintain the arch relax and it partially flattens. When you rise on the ball of the foot to take a step the arch is restored. The ball of the foot itself is at the level of the metatarsophalangeal (MTP) joints between the metatarsals and the toes.

You bear quite a lot of weight on the heads of the metatarsals as you spring off the foot at the end of a pace. The smaller toes do not contribute much to walking but a good deal of force goes through the big toe. In a normal pace the weight of the body first meets the ground at the heel then is gradually transferred forward along the outer margin of the foot, across the ball of the foot ending on the big toe. Fractures of bones along this path have more serious consequences for foot function.