Overview

The sacroiliac (SI) joints connect the sacrum — the triangular bone at the base of the spine — to the pelvis on each side. They are strong, relatively stable joints that transmit load between the spine and the legs, and they move very little.

SI joint dysfunction (also called SI joint pain or SIJ complex pain) is a common but underappreciated source of lower back and buttock pain. A 2025 international consensus guideline estimates that it contributes to pain in 15–30% of people with chronic axial low back pain below the level of L5.

Typical Pattern

One-sided pain over the buttock, the dimple above the buttock, or the very lower back
Worse with standing up from sitting, climbing stairs, single-leg standing, running or walking on uneven ground
Aching that can spread into the back of the thigh but rarely travels below the knee
Pain that may ease with lying down, but is not reliably worse with forward bending the way disc-related pain often is
A sense of the side "giving way" or feeling unstable in some people

Why It Develops

The SI joints sit between a flexible spine and two stiff pelvic bones, so they take substantial load during walking and single-leg activities. "Dysfunction" is an umbrella term: some people have too little movement (stiffness), some have too much, and the exact tissue responsible is rarely identifiable.

Contributing factors can include:

Weakness or poor control of the gluteal and core muscles
Leg-length differences or an altered walking pattern
Repetitive single-leg loading in running or sport
Previous lower back surgery or pelvic injury
Pregnancy and childbirth-related pelvic changes

How It Is Diagnosed

There is no single test that confirms SI joint dysfunction. A clinician usually combines:

The location and behaviour of the pain
Provocative tests such as compression, distraction, thigh thrust or FABER
A check of the lumbar spine, hips and nerve roots for other causes

Imaging mostly helps rule out fracture, inflammatory disease or nerve-root compression rather than diagnosing the SI joint itself. In some cases a diagnostic injection is used when the picture remains unclear, but it is not a first step.

Inflammatory causes such as sacroiliitis (seen in some types of inflammatory arthritis) behave differently — pain at rest with morning stiffness — and need a medical assessment rather than the usual mechanical approach.

Treatment

First-line care is conservative:

Education about the joint and how to pace activities
Load management: avoid prolonged sitting, break up long sits, and temporarily adjust single-leg loading
Progressive strengthening of the glutes, core and hip muscles
Graduated return to walking and sport
Manual therapy or mobility work in some cases

Injections (corticosteroid or other image-guided options) are reserved for people whose pain persists despite conservative care, and are always part of a plan that includes exercise rather than a stand-alone fix.

When to Get Assessed

Arrange an assessment if pain is one-sided and persistent, limits daily activity, or returns with every attempt to resume sport.

Seek urgent care if back or buttock pain comes with new leg numbness or weakness, loss of bladder or bowel control, numbness in the groin or saddle area, or severe pain after major trauma. Those patterns need prompt medical attention.

References

McCormick ZL, et al. "Consensus practice guidelines on sacroiliac joint complex pain from a multispecialty, international working group." Pain Medicine. 2025. https://pubmed.ncbi.nlm.nih.gov/41318933/
Simopoulos TT, et al. "A systematic evaluation of the therapeutic effectiveness of sacroiliac joint interventions." Pain Physician. 2015. https://pubmed.ncbi.nlm.nih.gov/26431129/

This information is for education only and is not a medical diagnosis. InjuryAtlas does not replace an assessment by a qualified health professional. If you have severe pain, visible deformity, numbness, loss of function, or symptoms that are getting worse, seek medical care promptly.

Sacroiliac Joint Dysfunction