Anatomy of the Foot: Part 1

When you consider the fact that each human foot is comprised of 26 individual bones, 20 intrinsic muscles (located on the foot), 11 extrinsic muscles (located on the lower leg but operate the foot), 33 joints, over 114 ligaments, and two pea-sized sesamoid bones, you probably don’t give your feet much thought… until they start to hurt. The foot is an extraordinarily complex and rugged structure, perfectly designed to keep you upright and mobile. Let’s take a closer look at the anatomy behind the foot.

Bones

The foot is subdivided into three sections:

Hindfoot: This area consists of 2 bones: the talus, which articulates with the tibia and fibula bones of the lower leg to form the talocrural, or ankle joint; and the calcaneus, which forms the heel of the foot and bears the brunt of your body weight.

Midfoot: The five bones of the midfoot help stabilize and support your body and form the arches of your feet.  You have 3 cuneiform bones (medial, intermediate, lateral), a navicular and cuboid bone.

Forefoot:  The forefoot is comprised on 19 bones. There are 5 long metatarsalbones which attach to the five toes. Each toe consists of 3 phalanges except for the big toe, which only contains two.  That’s a total of 14 phalanges or smaller bones in your toes alone.

The Three Arches

The foot consists of three distinct arches: the medial and lateral longitudinal arches, and the transverse arch.

The medial longitudinal arch is the highest and most prominent of the arches. It extends from the heel on the inner part of the foot to the ball of the foot along the first three metatarsals.

The lateral longitudinal arch is relatively less pronounced and closer to the ground than its medial counterpart. It runs from the heel on the outer part of the foot along the 4th and 5th metatarsals.

The transverse arch runs across the metatarsal heads along the ball of the foot.

Together, these three arches form the shape of your foot and determine to a large extent how your weight is distributed across its surface.

Ligaments

The arches of the feet are formed and supported by the smaller intrinsic muscles as well as its numerous ligaments. Ligaments are tough bands of tissue that attach bone to bone and provide stability and protection to the area. Of the hundreds of ligaments found in the foot, there are a few which are of particular importance.

The Deltoid ligament: (also known as the medial ligament) This ligamentoriginates on the medial malleolus (the large knob on the inner part of the ankle) and fans out to attach itself to the calcaneus, talus and navicular bones. The deltoid ligament is actually comprised of several ligaments designed to protect the inner part of the ankle from undue medial stress.

The Spring ligament: (also known as the calcaneo-navicular ligament) This ligament is located on the inner side of the foot and attaches the calcaneous to the navicular. This tiny little ligament is crucial in maintaining the medial longitudinal arch of the foot.

The Collateral ligament: (also know as the lateral ligament) This ligament, found on the outer part of the ankle, is also comprised of several ligaments. The purpose of this ligament is to protect the outer part of your ankle from undue lateral stress.

The Calcaneo-cuboid ligament: This tough band of tissue attaches the cuboid bone to your calcaneous on the outer part of the foot. This ligament plays a role in supporting the lateral longitudinal arch of the foot.

Ankle Sprains

A sprain is an injury to a ligament and its surrounding structure. You may have also heard of strains. A strain is an injury to a tendon (and/or its muscle), which attaches muscle to bone. There are two common forms of ankle sprains: Inversion and eversion sprains. Let’s start with the most common.

Inversion Sprains: 90 percent of all ankle sprains are inversion sprains. An inversion sprain occurs when the tendons and ligaments of the outer ankle are over-stretched. This usually occurs when the ankle rolls down and inward. In inversion sprains, the most commonly affected ligaments are the anterior talofibular and calcaneofibular ligaments of the collateral ligament and the calcaneo-cuboid ligament. Pain and swelling may occur along the outer ankle.

Eversion Sprains: Although eversion sprains are less common, they tend to be more serious. An eversion sprain occurs when the ankle rolls up and outward. Commonly affected tendons are the deltoid and spring ligaments. Pain and swelling typically occurs over the inner ankle and top of the foot.

In the second part of Anatomy of the Foot, we’ll discuss the various muscles and tendons that operate the foot and some of the conditions that can affect them.