The Anatomy of the Calcaneus

The calcaneus is the bone that forms the heel of the foot. It is one of the tarsals, the bones that make up part of the foot and ankle. The calcaneus is the largest bone of the foot and provides the foundation for all of the other tarsals and metatarsals.

The calcaneus strikes the ground with every footfall when running or walking. Stress fractures of the calcaneus and inflammation of the plantar fascia ligament that is attached to the calcaneus are two of the most common causes of foot pain.

Anatomy

The calcaneus is one of seven tarsal bones that make up the foot. The calcaneus is a short bone, a type of bone meaning that it is about as long as it is wide. All of the tarsals are considered short bones.

The calcaneus is primarily made up of trabecular bone (spongy bone). The density of the trabecular bone in the calcaneus is directly related to its strength. Runners and those with higher body weight develop more bone density in the calcaneus due to pressures placed on it with walking and running.

Structure

The calcaneus is a complicated bone with lots of different surfaces, attachments, and insertion points.

The posterior (back) portion is the heel. The Achilles tendon insertion point is on the superior aspect (top) of the posterior part of the calcaneus. There are two bursae (fluid-filled sacs that act as cushions) in front (internal) and behind (external) the insertion point for the Achilles tendon. The middle surface of the posterior portion of the calcaneus is the insertion point of the calcaneal tendon.

The most superior portion of the calcaneus connects to a tarsal bone, called the talus, above it. The talus articulates with the calcaneus on three surfaces: the anterior talar articular surface, the middle talar articular surface and, the largest, the posterior talar articular surface.

The entire anterior (front) surface of the calcaneus articulates with the cuboid bone, another tarsal bone. There are several additional processes (protuberances) situated around the calcaneus that act as channels and insertion points for other tendons as well as assisting with balance.

In childhood, there is an apophysis (growth plate) present near the bulbous surface of the posterior calcaneus. This apophysis solidifies, or fuses, around 15 years of age. In some females, it doesn't solidify until 18 years old. In some males, it doesn't finish ossifying (hardening into solid bone) until 22 years of age.

Location

The calcaneus is at the posterior (back) of the foot where the heel is located. This location allows the calcaneus to act as a fulcrum point for flexion and extension of the foot. Flexion is what happens when you lift your toes off the floor as you're about to tap your foot. Extension is what happens when you're pushing on the gas pedal.

Anatomical Variations

There are several anatomical variations of the calcaneus that can be seen on medical images. Some of these may be related to certain medical conditions, while others may not result in any complaint and are noted only because they are often identified by radiologists.

• Pseudofracture of the apophysis is a partially ossified apophyseal plate that appears on an X-ray as if it was a fracture. This is a normal variant of the calcaneus and does not require treatment.
• Congenital tarsal coalition is a connection between tarsals, usually the calcaneus and talus, that prevent the tarsals from articulating properly. The coalition can be from ossification (bone fusion), fibrous tissue, or a buildup of cartilage.
• Calcaneal pseudocysts or calcaneal pseudotumors are very common normal variants in images of the calcaneus caused by variations in the density of bone. Calcaneal pseudocysts are usually only present in young patients and resolve with age.
• A nutrient foramen (a hole to allow blood vessels) can form in the spongy bone of the calcaneus. This is a normal variation that is not very common, but completely benign.

Function

The calcaneus provides one point of a solid tripedal surface for the foot. It also provides a fulcrum for extension and flexion of the foot.

The Achilles tendon is the strongest tendon in the body. It is the common tendon for the gastrocnemius (calf) muscle. Think about how short the calcaneus is as a lever, but how much force it takes for that short lever to lift the entire body weight. The body is able to do that using just one of the two Achilles tendons.

Associated Conditions

Obviously, direct trauma to the calcaneus will be a cause of pain. However, there are several non-traumatic or repetitive stress injuries that can cause pain in high impact bones like the calcaneus.

Heel pain is a common symptom associated with the calcaneus. There are several causes of heel pain.

Calcaneal Apophysitis

Calcaneal apophysitis is the most common cause of heel pain in children. It is an inflammation of the calcaneal apophysis that is likely caused by repetitive strikes from running or jumping.

Bursitis

A bursa is a fluid-filled sac that acts as a bumper or cushion between potentially tender areas and tissue that can irritate them. Bursitis that can cause heel or foot pain is an inflammation of the bursae that are commonly found around the insertion points of tendons or between articulated tarsal bones such as the talus and calcaneus (talocalcaneal joint).

Plantar Fasciitis

Plantar fasciitis is the most common cause of heel and foot pain in adults. The plantar fascia tendon helps hold the shape of the bottom (plantar surface) of the foot. This common tendonitis occurs frequently in runners and can be hard to remedy.

Stress Fractures

Repetitively striking the heel can lead to the development of stress fractures in the calcaneus. These are often minor cracks that cause pain in the foot. Rarely is a stress fracture very large, but it takes time to heal because it is in the heel.

Avulsion Fractures

When a tendon rips free of an insertion point, it is known as an avulsion fracture. Usually, the tendon doesn't come apart from the bone, but the bone to which it is attached might break loose, hence the term.

There are two major tendon insertion points on the calcaneus: the Achilles tendon and the plantar fascia tendon. Achilles tendon ruptures are common, but avulsion fractures are not. Simple Achilles tendon ruptures cause pain in the ankle or calf more than in the heel.

Rehabilitation

Calcaneus injury treatment depends on the type and severity of the injury. In general, your healthcare provider may try to use conservative, nonsurgical treatment first. If that doesn't work, surgery might be necessary to correct an injury.

Rehabilitation depends on the severity of the injury and on the choice of treatment.

Treating Plantar Fasciitis

Physical therapy using stretches, massage, and exercises is the most common treatment for plantar fasciitis. With proper guidance on technique, many patients can treat plantar fasciitis at home.

If the plantar fasciitis is severe, your healthcare provider may prescribe a brace and splint to help your plantar fascia heal. In some cases, you will only wear the brace at night while sleeping to assist in stretching the plantar fascia.

Treating Calcaneus Fractures

If the bone is not displaced due to a fracture, meaning that all the pieces are in the right places, nonsurgical treatment might be appropriate. This is the most common type of treatment for patients with stress fractures of the calcaneus. This sort of conservative management uses splints or braces and requires that the patient keep pressure off of the heel while it heals.

In the case of severe trauma and complete fractures with displacement, it is often necessary for surgical repair. Once the surgery is done, the patient will still be required to keep pressure off of the heel. Usually, the patient will use braces or splints to hold the heel in the correct position and prevent movement.