SI joint anatomy and function
The SI joints connect the triangular sacrum at the base of your spine to the ilium bones of the pelvis. They have strong ligaments and irregular joint surfaces, which make them very stable.
Unlike the hip or knee, they don’t have a large range of motion. Instead, they allow small movements that help transfer load between the spine and legs.
In essence, these joints act like a stable “bridge” between your upper and lower body, supporting everyday activities such as walking, bending, and lifting.
Causes and risk factors
SI joint dysfunction may occur when the joint moves too much or too little. It can be affected by pregnancy, pelvic injury, falls, or lifting and twisting movements.
Factors such as arthritis, previous spinal surgery, and differences in leg length may also increase stress on the joint over time.
Common symptoms
SI joint-related pain can be felt as an ache or sharp pain on one side of the lower back, just off the spine. It can spread into the buttock or down the thigh.
It may feel worse with prolonged standing, walking uphill or stairs, rolling over, and activities involving bending and lifting.
Assessment and management
Assessment begins with a discussion of your symptoms, including where the pain is felt, how it started, and what makes it better or worse.
We also assess posture and movement to see how your spine, hips, and pelvis work together. In some cases, specific clinical tests may be used, and imaging such as X-rays or scans may be considered if clinically appropriate.
Management may include exercises to support pelvic stability, advice on movement and posture, and strategies to reduce strain during daily activities.
