What Parts of the Body Does AS Affect?

Reviewed by: HU Medical Review Board | Last reviewed: February 2019 | Last updated: June 2019

Ankylosing spondylitis (AS) usually affects the spine, but other joints in the body can also be affected. AS causes chronic inflammation of the affected joints where the ligaments and tendons attach to the bone, called enthesitis. Enthesitis can cause tenderness or pain and may be called "hot spots." The chronic inflammation can lead to bone being formed between the joint, called ankylosis or bony fusion. This can cause stiffness and a loss of mobility.1,2 The word "spondylitis" means inflammation of the spine and "ankylosing" means abnormal stiffness and fusion of a joint.3

AS varies in different people by the level of severity and which joints are affected. The parts of the body that AS may affect are described below.

Sacroiliac joints

AS most often begins in the sacroiliac joints - the joints located between the bottom of the spine (the sacrum) and the ilium of the pelvis. This can cause low back pain, which is the most common symptom experienced by people with AS. The pain may come on gradually but can become constant and severe. Some people have pain that comes and goes. Symptoms are usually worse at night or in the morning and feel better with activity.1,4

The SI joint

Parts of the spine

In medicine, the spine is sometimes called the axial skeleton. It is divided into 3 sections5:

  • The first section is the 7 vertebrae at the top of the spine. These vertebrae are called the cervical spine. They begin at the base of the skull and make up the neck. They are referred to as C1-C7.
  • The thoracic spine is the 12 vertebrae in the mid-section of the spine. This is where the ribs attach. These vertebrae are referred to as T1-T12.
  • The lumbar section of the spine is at the bottom. The vertebrae in this section are referred to as L1-L5.

Parts of the spine

AS can progress from the sacroiliac joints to the joints between the vertebrae. The chronic inflammation of the ligaments that attach to the spine can lead to the development of bone in the vertebral joints. This is called calcification. This calcification of the spinal ligaments is called syndesmophytes. As the condition develops and the spine becomes more immobilized by the formation of bone in the joints, the spine can take on the appearance of bamboo on x-rays. This is referred to as "bamboo spine." The presence of bamboo spine increases a person's risk of fractures in the vertebrae.6

Bony fusion of the vertebrae causes pain and stiffness and can lead to a lack of flexibility in the spine. Some people with AS have difficulty rotating or twisting their spine.3 Fusion of the joints between the ribs and spine or between the ribs and the breastbone can make it difficult to fully expand the chest cavity. This can cause chest pain or difficulty taking deep breaths.2

Loss of spine curvatureOther parts of the body affected by ASAS can cause various patterns of pain and stiffness. No two people have the same progression. Areas of the body AS may affect include:Hips or shoulders - Approximately 30% of people with AS experience hip or shoulder pain. When AS affects the hips, it may cause referred pain. This is a confusing symptom that causes pain in the groin, the front of the thigh or in the knees.2Eyes - Many people with AS have inflammation in the eyes, called uveitis or iritis. This can cause eye pain and sensitivity to light, called photophobia.7Jaw - While rare, about 15% of people with AS have jaw issues, which can make it difficult to open the mouth and may make eating hard.2Wrist or fingers - Sausage shaped swelling (sausage digits) can affect one or several fingers or toes. The wrist or joints in the fingers are affected in approximately 5% of people with AS.2Heels or toes - Pain and swelling of the Achilles tendon are common. About 30% of people with AS have pain in their heels and about 5% have pain in the joints in the toes.2AS can also cause other complications in the body. This can include complications involving the heart or the lungs.1

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