Tendons are the tissues that attach your muscles to your bones. Ligaments are what attach your bones to one another. The places where your tendons and ligaments meet your bones are called entheses.
Sometimes, these connection points can get inflamed and become painful because of injury, overuse, or disease. This is known as enthesitis, also sometimes called enthesopathy.
Inflammation of the entheses can cause new bone tissue to form. That new bone tissue gets in the way of normal movement and function – like a bone spur on your heel.
Enthesitis is common in some forms of arthritis, including psoriatic arthritis and ankylosing spondylitis. It also can happen in some children with juvenile idiopathic arthritis (also known as juvenile rheumatoid arthritis).
Common spots for enthesitis to happen are around your heel, knee, hip, toes, fingertips, elbow, backbone, and the bottom of your foot. You’ll feel pain and stiffness, especially when you’re moving. You also might notice swelling around those areas.
This pain can be different from other types of arthritis pain because you usually feel it next to a joint or spread out over a wider area rather than inside a joint.
Soreness at the back of your heel caused by enthesitis is sometimes called Achilles’ tendonitis. This pain can make it hard for you to run or climb stairs.
As the condition gets worse, it can make your tendons and ligaments thick, swollen, or hard, and that makes movement even more painful and difficult. These changes can often be seen with an imaging test such as an ultrasound or MRI.