Rheumatoid Arthritis of the Foot & Ankle
Rheumatoid arthritis is a chronic disease that attacks multiple joints throughout the body. It most often starts in the small joints of the hands and feet, and usually affects the same joints on both sides of the body.
More than 90% of people with rheumatoid arthritis (RA) develop symptoms in the foot and ankle over the course of the disease.
Rheumatoid arthritis is an autoimmune disease. This means that the immune system attacks its own tissues. In RA, the defenses that protect the body from infection instead damage normal tissue (such as cartilage and ligaments) and soften bone.
How It Happens
The joints of your body are covered with a lining — called synovium — that lubricates the joint and makes it easier to move. Rheumatoid arthritis causes an overactivity of this lining. It swells and becomes inflamed, destroying the joint, as well as the ligaments and other tissues that support it. Weakened ligaments can cause joint deformities — such as claw toe or hammer toe. Softening of the bone (osteopenia) can result in stress fractures and collapse of bone.
Rheumatoid arthritis is not an isolated disease of the bones and joints. It affects tissues throughout the body, causing damage to the blood vessels, nerves, and tendons. Deformities of the hands and feet are the more obvious signs of RA. In about 20% of patients, foot and ankle symptoms are the first signs of the disease.
Cause & Symptoms
The exact cause of RA is not known. There may be a genetic reason — some people may be more likely to develop the disease because of family heredity. However, doctors suspect that it takes a chemical or environmental “trigger” to activate the disease in people who genetically inherit RA.
The most common symptoms are pain, swelling, and stiffness. Unlike osteoarthritis, which typically affects one specific joint, symptoms of RA usually appear in both feet, affecting the same joints on each foot.
Difficulty with inclines (ramps) and stairs are the early signs of ankle involvement. As the disease progresses, simple walking and standing can become painful.
Hindfoot (Heel Region of the Foot)
The main function of the hindfoot is to perform the side-to-side motion of the foot. Difficulty walking on uneven ground, grass, or gravel are the initial signs. Pain is common just beneath the fibula (the smaller lower leg bone) on the outside of the foot.
As the disease progresses, the alignment of the foot may shift as the bones move out of their normal positions. This can result in a flatfoot deformity. Pain and discomfort may be felt along the posterior tibial tendon (main tendon that supports the arch) on the inside of the ankle, or on the outside of the ankle beneath the fibula.
Midfoot (Top of the Foot)
With RA, the ligaments that support the midfoot become weakened and the arch collapses. With loss of the arch, the foot commonly collapses and the front of the foot points outward. RA also damages the cartilage, causing arthritic pain that is present with or without shoes. Over time, the shape of the foot can change because the structures that support it degenerate. This can create a large bony prominence (bump) on the arch. All of these changes in the shape of the foot can make it very difficult to wear shoes.
Forefoot (Toes and Ball of the Foot)
The changes that occur to the front of the foot are unique to patients with RA. These problems include bunions, claw toes, and pain under the ball of the foot (metatarsalgia). Although, each individual deformity is common, it is the combination of deformities that compounds the problem.
Medical History and Physical Examination
After listening to your symptoms and discussing your general health and medical history, your doctor will examine your foot and ankle.
Skin. The location of callouses indicate areas of abnormal pressure on the foot. The most common location is on the ball of the foot (the underside of the forefoot). If the middle of the foot is involved, there may be a large prominence on the inside and bottom of the foot. This can cause callouses.
Foot shape. Your doctor will look for specific deformities, such as bunions, claw toes, and flat feet.
Flexibility. In the early stages of RA, the joints will typically still have movement. As arthritis progresses and there is a total loss of cartilage, the joints become very stiff. Whether there is motion within the joints will influence treatment options.
Tenderness to pressure. Although applying pressure to an already sensitive foot can be very uncomfortable, it is critical that your doctor identify the areas of the foot and ankle that are causing the pain. By applying gentle pressure at specific joints your doctor can determine which joints have symptoms and need treatment. The areas on the x-ray that look abnormal are not always the same ones that are causing the pain.
Other tests that your doctor may order to help confirm your diagnosis include:
X-rays. This test creates images of dense structures, like bone. It will show your doctor the position of the bones. The x-rays can be used by your doctor to make measurements of the alignment of the bones and joint spaces, which will help your doctor determine what surgery would best.
Computerized tomography (CT) scan. When the deformity is severe, the shape of the foot can be abnormal enough to make it difficult to determine which joints have been affected and the extent of the disease. CT scans allow your doctor to more closely examine each joint for the presence of arthritis.
Magnetic resonance imaging (MRI) scan. An MRI scan will show the soft tissues, including the ligaments and tendons. Your doctor can assess whether the tendon is inflamed (tendonitis) or torn (ruptured).