I feel like the medical system failed us. Our little girl (five years old) came down with a fever and an earache. She was treated with antibiotics for an ear infection but then started complaining her knee hurt. After a couple of days of limping around, we took her back to the doctor. She couldn’t find anything wrong and sent us home. We ended up taking her to the emergency department over the weekend. She was diagnosed with septic sacroiliitis. Why was that so difficult to figure out?

Septic sacroiliitis is an infection of the sacroiliac (SI) joint. There is an SI joint located to the right and left of the sacrum where the pelvic bones meet the sacral bone. The condition is very rare and difficult to diagnose.

As in the case of your daughter, the pain can present at a joint other than the one affected. Back, buttock, hip, SI, and knee pain are all possible with this condition. Having already treated your child with an antibiotic (and possibly seeing the inner ears were clear), the physician likely assumed the problem was resolved.

And it’s true that the ear infection was cleared up. However, the infectious agent traveled along the blood stream to this distant site and set up housekeeping there. Symptoms of pain and limping without obvious changes in the joint (redness, swelling, heat) make it easy to dismiss the problem.

Most cases of septic sacroiliitis in children are, in fact, misdiagnosed. The most common false diagnoses given are arthritis, disc herniation, or tumor. In many cases, it isn’t until the condition gets worse and an emergency visit is needed that the diagnosis is finally made.