What is foot tendinitis?
The tendons that are most likely to get tendinitis are the: 
- Achilles tendon, which attaches the calf muscle (on the back side of your lower leg) to the back of the heel. 
- Posterior tibial tendon, which attaches the inside of the calf muscle to the bones on the inside of the foot. 
- Peronealtendon, which attaches the outside of the calf to the outside of the foot. 
Foot tendinitis is when one of these tendons becomes inflamed. When this happens, the tendon will swell and become irritated. In some cases, the tendon may harden (calcify) or cause a bone spur to grow.
Symptoms
Pain in the foot or ankle, and/or weakness are the most common symptoms of foot tendinitis. The pain will often get worse when trying to walk, or when doing other activities. The pain may also feel as though it moves down the foot or up the leg. Other symptoms may include: 
- Achiness in the foot and/or ankle 
- Snapping sounds or sensations in the ankle 
- Thickness at the heel or at the bottom of the calf muscle 
- Flat foot 
- Pain on the inside or back of the ankle 
More Information
Causes
Foot tendinitis is sometimes caused by normal use and age but is more often brought on by overuse. This is most common in athletes because they perform the same motions over and over. 
People that have flat feet also have a tendency to develop foot tendinitis. Sometimes tendinitis happens because the tendon is injured. 
Foot tendinitis can also occur with foot and ankle problems that have caused damage to the area, such as: 
- Arthritis 
- Muscle tears 
- Dislocation 
- Other inflammation 
- Flat feet
Diagnosis & Tests
To diagnose foot tendinitis, your doctor will ask about your health history and your injury, and perform a physical exam. During this exam, the doctor may press on the area where the tendons attach to the calf or foot to see if they can feel any hardness or swelling. Your doctor may also ask you to move your foot and ankle to check your range of motion. 
If your doctor finds that your symptoms are consistent with foot tendinitis, imaging tests, such as an x-ray or MRI may be ordered to confirm or rule out tendinitis. 
Treatment
Treatment will depend on the severity and location of the tendinitis. If your case is mild, non-surgical treatments, such as rest, ice, and medicine may be enough. If your case is more severe, your doctor may recommend steroid injections, physical therapy, or surgery. 
If your doctor recommends surgery, they will help you develop a rehabilitation plan that will help you with recovery. You may have to wear a brace or use another type of support during this recovery phase.