Sacrum, ilium and sacroiliac joints
sacroiliac joints

What is sacroiliitis?

Sacroiliitis is the inflammation of one or both of your sacroiliac joints. These two joints are located where the sacrum (the triangular last section of the spine) meets the ilium (a part of the pelvis).

Sacroiliitis is a common source of lower back pain or pain in the buttocks or thighs. It is often difficult to diagnose since many other conditions cause pain in the same locations.

How common is sacroiliitis?

Doctors don’t know for sure how many people live with sacroiliitis. However, it has been estimated that between 10 percent and 25 percent of people who report low back pain may have sacroiliitis.

What causes sacroiliitis?

Inflammation of the sacroiliac joint causes most of the symptoms of sacroiliitis. Many medical conditions cause inflammation in the sacroiliac joint, including:

  • Osteoarthritis -This type of wear-and-tear arthritis can occur in the sacroiliac joints and results from the breakdown of ligaments.
  • Ankylosing spondylitis - This is a type of inflammatory arthritis of the joints of the spine. Sacroiliitis is often an early symptom of ankylosing spondylitis.
  • Psoriatic arthritis - This inflammatory condition causes joint pain and swelling as well as psoriasis (scaly patches on the skin). Psoriatic arthritis can cause inflammation of the spinal joints, including the sacroiliac joints.

Other causes of sacroiliitis include:

  • Trauma - A fall, motor vehicle accident, or other injury to the sacroiliac joints or the ligaments supporting or surrounding the sacroiliac joint can cause symptoms.
  • Pregnancy - Hormones generated during pregnancy can relax the muscles and ligaments of the pelvis, causing the sacroiliac joint to rotate. The weight of pregnancy can also stress the sacroiliac joint and lead to wearing of the joint.
  • Pyogenic sacroiliitis - This is a rare infection of the sacroiliac joint caused by the bacteria Staphylococcus aureus.

What are the symptoms of sacroiliitis?

Common symptoms of sacroiliitis include pain that:

  • Occurs in the lower back, buttock, hip, or thigh
  • Gets worse after long periods of sitting or standing, or getting out of a chair
  • Worsens after rotating your hips
  • Feels sharp or stabbing, or dull and achy

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