What Part of the Body is Affected by AxSpA?

Reviewed by: HU Medical Review Board | Last reviewed: May 2020 | Last updated: February 2021

Axial spondyloarthritis (AxSpA) is a type of inflammatory condition that causes arthritis, specifically where ligaments and tendons attach to bones.1 AxSpA is mainly concentrated in the spine and pelvic joints. Knowing more about your anatomy can be helpful in understanding just how AxSpA can affect the body and why certain symptoms may occur.

What are joints, ligaments, and tendons?

AxSpA affects joints, ligaments, and tendons. Each of these has a different role to play in mobility and movement.

Joints are the areas where two or more bones meet.2 Most of the time, joints are mobile, which means they enable the bones to move in various ways.

Ligaments connect bones. They are elastic bands of connective tissue and very strong.2 Ligaments surround a joint and provide support for the joint so that it doesn’t move too much, or more than it is supposed to.2

Tendons are also a type of connective tissue that is very tough, and these are on each side of the joint. Tendons attach to the muscles of a joint that control its movement.2 Muscles connect to bones with the help of tendons.2

Figure 1. Parts of a basic human joint

The anatomy of a human joint which includes muscle, tendon, ligament, and bone.

What happens with AxSpA and the bones?

With AxSpA, unlike other types of arthritis where bone and cartilage are damaged, new bone formation occurs. When new bone formation happens, bone appears where it is not supposed to and can actually fuse existing bones together, affecting range of motion and normal use of joints.3

What are the differences between inflammatory disease and wear-and-tear arthritis?

Arthritis caused by wear-and-tear is called osteoarthritis, and is from physical use. Over time, joints get natural wear-and-tear, causing pain or swelling. This can also occur because of an injury.3 This tends to occur in older people over the age of 50.3

Inflammatory arthritis typically has an autoimmune component to it and is a chronic condition.3 It can affect people of any age, not just older individuals. In inflammatory disease, the body mistakes its own tissues as foreign and attacks it, causing inflammation.3

Inflammatory arthritis conditions have periods where symptoms get worse (“flare-ups”) and remissions, where no symptoms are occurring. In wear-and-tear arthritis, these alternating periods do not occur.

Common sites of pain and inflammation in AxSpA

AxSpA is characterized by persistent inflammation of the sacroiliac joints, where the sacrum (the base of the spine) meets the hip bones, or ilium. This causes back pain, changes in posture, stiffness, and changes in the skeletal spine.4

The very name of AxSpA centers on the spine, pelvis, and hips, and this is where pain and inflammation tend to center in the condition.

Figure 2. The lumbar spine, pelvis, sacrum, and ilium

The anatomy of the pelvis which includes the sacroiliac joint, the sacrum, and the ilium.

Natural course of AxSpA

For many people with AxSpA, the pain, fatigue, and stiffness, along with other symptoms, tend to have periods of flare-ups and remissions. During flare-ups, a patient with AxSpA may have more symptoms, like greater pain and discomfort. After a period of time, this will stop, and no symptoms will occur. This is the remission period.5

Treatment seeks to minimize flare-ups and extend periods of remission.

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