It can be extremely confusing to figure out the difference between hip and SI (sacroiliac) joint pain. But being able to identify which one is the culprit is crucial when you are looking to find relief. Your SI joint connects your tailbone (sacrum) and your pelvis. The SI joint is very fibrous and only moves a few millimeters. On the other hand, your hip is much less stable and allows your entire leg to move in every plane of motion.
While the hip and SI joints are very different in structure and function, they share similar pain patterns, making it difficult to tell one from the other. It’s common to have SI joint pain mimic low back pain. Bending backward usually aggravates SI joint pain due to the compression that happens in the joint as you move. Hip pain is more likely to occur when you walk or try to bring your knees to your chest.
Hip Pain: characterized by pain with walking, weight-bearing, and rotating the leg
SI Joint Pain: characterized by difficulties while standing, walking, climbing stairs, and getting out of the car.
Low Back Pain: characterized by pain that radiates into the buttock or leg and may travel down to the foot
Science Source:
Sacroiliac Joint Dysfunction. Spine-Health 2021