Sacroiliitis is an inflammation affecting one or both sacroiliac joints. It is a common cause of lower back pain, buttock pain, and thigh pain.
The sacroiliac joints are located where the sacrum (lower spine) and ilium (pelvis) meet. When either of these joints becomes swollen, it can cause stiffness and pain in the lower back and buttocks as well as in one or both legs. Standing or sitting for an extended period of time and climbing stairs can worsen the pain.  Sacroiliitis can be caused by trauma, pregnancy, infection, or an underlying medical condition. It is often difficult to diagnose as many other illnesses can cause pain in the same area of the body. It is managed through medication and physical therapy. If left untreated, it can lead to a loss of mobility.


The most common symptom of sacroiliitis is pain felt in the legs, foot, and groin, but most often in the buttocks and lower back. Physical activity can help reduce the pain associated with sacroiliitis. However, the following action may worsen the discomfort:

  • Being heavier on one leg than the other.
  • Spending long periods of time sleeping or sitting.
  • Spending long periods of time standing.
  • Running or walking with long strides.
  • Going up and down the stairs.
  • After rotating the hips.

Visit a healthcare provider if pain in the lower back, buttocks, or thighs persists. A proper diagnosis is necessary for correctly treating or managing the pain.


Sacroiliitis can develop due to various reasons, including:

  • Injury: Trauma to the sacroiliac joints or the ligaments that support or surround these joints, caused by a fall, car accident, or other incidents, can lead to sacroiliitis.
  • Arthritis: Chronic illnesses such as psoriatic arthritis, osteoarthritis, and ankylosing spondylitis can result in inflammation of the sacroiliac joint. Psoriatic arthritis is an inflammatory condition that causes joint pain and swelling along with psoriasis. Osteoarthritis, on the other hand, is a form of wear-and-tear arthritis that can develop in the sacroiliac joints and is caused by the breakdown of ligaments. Ankylosing spondylitis is a type of inflammatory arthritis of the joints of the spine. Sacroiliitis is often an early symptom of ankylosing spondylitis.
  • Pregnancy: During pregnancy, the extra weight and altered walking pattern can put pressure on the sacroiliac joints, and the hormones produced can cause the pelvic muscles and ligaments to loosen, resulting in the twisting of the sacroiliac joint.
  • Infection: Pyogenic sacroiliitis, an unusual sacroiliac joint infection caused by the bacteria Staphylococcus aureus, can also result in sacroiliitis.