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The bones of the feet are commonly divided into three parts: the hindfoot, midfoot, and forefoot. Seven bones — called tarsals — compose the hindfoot and midfoot. Of these bones, the calcaneus, talus, and navicular are most commonly involved in tarsal coalition.

The calcaneus, talus, and navicular bones are those most often affected by tarsal coalition.

A tarsal coalition occurs when two bones grow into one another, connected by a bridge of bone, cartilage, or strong, fibrous tissue. These bridges are often referred to as "bars" and they can cover just a small amount of the joint space between the bones, or a large portion of the space.

The two most common sites of tarsal coalition are between the calcaneus and navicular bones, or between the talus and calcaneus bones. However, other joints can also be affected.

It is estimated that one out of every 100 people may have a tarsal coalition. In about 50% of cases, both feet are affected. The exact incidence of the disorder is hard to determine because many coalitions never cause noticeable symptoms.

In most people, the condition begins before birth. It is caused by a gene mutation that affects the cells that produce the tarsal bones. Although the coalition forms before birth, its presence is often not discovered until late childhood or adolescence.

This is because babies' feet contain a higher percentage of soft, growing cartilage. As a child grows, this cartilage mineralizes (ossifies), resulting in hard, mature bone. If a coalition exists, it may harden, too, and fuse the growing bones together with a solid bridge of bone or fibrous tissue similar to a scar. The ossification of the coalition typically happens between ages 8 and 16, depending upon which bones are involved. As a result, the hindfoot stiffens, causing pain and other symptoms.

The stiffness and stress that tarsal coalitions produce may lead to arthritis over time.

This x-ray image of a right foot shows a tarsal coalition between the navicular bone and the calcaneus bone.

Courtesy of Texas Scottish Rite Hospital for Children

Many tarsal coalitions are never discovered because they do not cause symptoms or any obvious foot deformity. When symptoms do occur, they may include:

• Stiff, painful feet. The pain usually occurs below the ankle around the middle or back half of the foot.
• A rigid, flat foot that makes it difficult to walk on uneven surfaces. To accommodate for the foot's lack of motion, the patient may roll the ankle more than normal, which may result in recurrent ankle sprains.
• Increased pain or a limp with higher levels of activity.

Tarsal coalitions only require treatment if they are causing symptoms.

Surgical Treatment

When nonsurgical treatments are not effective at easing pain or improving function, your doctor may consider surgery.

The surgical procedure your doctor recommends will depend on the size and location of the coalition, as well as whether the joints between the bones show signs of arthritis.

• Resection. In this procedure, the coalition is removed and replaced with muscle or fatty tissue from another area of the body. This is the most common surgery for tarsal coalition because it preserves normal foot motion and successfully relieves symptoms in most patients who do not have signs of arthritis.

These CT cross-section images show a patient with coalitions between the calcaneus and talus in both feet. At the time of this scan, the coalition on the left foot had been resected, and the right foot was awaiting the procedure.

Reproduced with permission from Pierz KA Tarsal coalition. Orthopaedic Knowledge Online Journal 8/1/2009. Accessed December 2013.

• Fusion. Larger, more severe coalitions that cause significant deformity and also involve arthritis may be treated with joint fusion. The goal of fusion is to limit movement of painful joints and place the bones in the proper position. In fusion for tarsal coalition, the bones may be held in place with large screws, pins, or screw-and-plate devices.

Depending upon the type and location of your surgery, a cast will be required for a period of time to protect the surgical site and prevent you from putting weight on the foot. Casts are typically replaced with walking boots, and your doctor may recommend physical therapy exercises to begin restoring range of motion and strength.

Your doctor will determine when it is safe for you to begin putting weight on your foot. Arch supports or orthotics may also be helpful in stabilizing the joint, even after surgery.

Although it may take several months to fully recover, most patients have pain relief and improved motion after surgery.