Ankylosing spondylitis (AS), a form of inflammatory arthritis, can lead to problems with pain, mobility, and spinal fusion. Less commonly, it can affect other parts of your body.

AS is a type of inflammatory arthritis primarily known for affecting your spine. It’s also considered a type of spondyloarthritis.

This condition is most common in adults younger than 45, as well as those with a family history of AS or other autoimmune diseases like psoriasis or Crohn’s disease.

Over time, you may experience back pain from inflammation in your spine, leading to pain and stiffness. In severe cases, AS can cause the vertebrae in your spine to fuse together.

But, the effects of AS can go beyond your spine, with inflammation affecting joints in your hips, knees, and even your ankles and feet. These effects are not as common as spinal inflammation and pain, but they’re still important to consider when you have AS.

Learn more about how AS can affect the joints in your ankles and feet, as well as what treatment options are available.

AS usually affects your spine first, so you’re more likely to experience symptoms such as back pain and stiffness. But, this arthritis can cause issues throughout your body, including your ankles. This can cause stiffness, pain, and reduced mobility.

If you develop AS in your ankles, you may experience symptoms along the affected joints, such as:

  • swelling
  • pain
  • tenderness to the touch
  • warmth along the skin over the area

You may also notice that your symptoms are worse upon waking up in the morning, or after other times of prolonged rest. This is also the same with spinal problems from AS.

Overall, researchers believe AS of the ankle joint isn’t common, but fusion between bones is a possible complication to consider. Affected ankle joints may also look like boots on imaging scans, giving the nickname “boot sign.”

AS can affect other joints in your feet outside of the ankle.

Deformities in the foot may be possible in AS, according to a 2022 study that looked at the data of 110 people with AS. The authors concluded that these foot problems most likely developed from enthesopathy and problems in hip joints.

Enthesopathy (also called enthesitis) describes a painful inflammation that develops at the site where your bones and tendons or ligaments connect.

Enthesitis is one possible known issue in AS. It can affect your Achilles tendon behind your heel, causing Achilles tendinitis. It may also develop underneath your heel, increasing the risk of plantar fasciitis.

Enthesitis can affect other areas of your body as well, and is common in spondyloarthritis overall.

According to one 2022 study, it’s possible for fusion to develop in your foot due to AS. The authors noted a 69-year-old man who developed fusion between the bones of his midfoot, ankle, and hindfoot, affecting both feet.

While such instances are rare, it’s important to look out for changes in your feet that could indicate AS progression or other difficulties with your joints. The sooner joint issues are diagnosed and treated, the better the overall outcome.

Rheumatoid arthritis (RA)

Another possibility to consider is the existence of both rheumatoid arthritis (RA) and AS at the same time. RA is a type of autoimmune disease that affects joints throughout your body, but usually the smaller ones in your hands and feet.

According to a 2022 review of 81 people, researchers found that 53% of them had signs of RA on imaging tests, while 83% had lower inflammatory back pain.

The researchers stated that having both RA and AS is considered rare, but they cautioned that it’s worth further investigation to see whether one condition affects the development of the other.

There’s currently no cure for AS, so it’s important to speak with a doctor if you suspect new or worsening symptoms of this type of arthritis. This includes symptoms in your ankles and other parts of your feet.

Like other types of inflammatory and autoimmune diseases, AS tends to cause symptoms that come and go. When you have worsening symptoms, this is known as a flare. Consider getting medical help if you’re experiencing a new AS flare, as you may need additional treatment.

It’s also recommended to see a doctor if you’re experiencing symptoms of AS in your feet and ankles that are severe enough to limit your everyday activities, such as standing and walking. Changes in gait are also worth discussing with a doctor for further assessment.

To help diagnose AS in your ankles and feet, a doctor may:

  • examine the joints along your ankles and feet
  • ask you to move your feet to assess pain, flexibility, and mobility
  • order magnetic resonance imaging (MRI) tests, especially in early stages of AS
  • order X-rays of the ankles and feet to confirm AS and monitor its progression

The goal of treatment for AS is to help minimize pain and control inflammation that could lead to further disease progression and complications. This also includes joints in your feet and ankles.

Possible treatment options for foot and ankle pain caused by AS include:

  • an evaluation by a podiatrist or orthopedic surgeon to optimize condition management
  • over-the-counter (OTC) pain medications
  • injectable corticosteroids to target pain in specific joints
  • biologics or janus kinase (JAK) inhibitors to control systemic inflammation from AS
  • physical therapy to help reduce pain while improving mobility and flexibility
  • assistive devices to help you walk safely
  • regular exercise to improve joint health, as well as to protect your heart
  • surgery (in cases of severe joint damage only)

While foot and ankle joint issues aren’t as common in AS, these are possibilities worth discussing with a doctor. This is especially the case if you have an AS diagnosis and are currently experiencing ankle or foot pain and swelling.