Sacroiliac joint pain typically feels like a deep, steady ache in the lower back or buttock, usually on one side. It accounts for an estimated 15% to 30% of all chronic lower back pain cases, yet it’s frequently mistaken for a disc problem or sciatica because the pain can spread into the hip, groin, or thigh.
Where You Feel It
The hallmark location is right over the SI joint itself, a small area just to one side of the base of your spine, near the dimples of your lower back. In studies using pain-mapping techniques, 100% of confirmed SI joint pain patients reported buttock pain directly overlying the joint. From there, the pain commonly radiates into the upper thigh or groin on the same side. Some people feel it wrapping around the hip or traveling partway down the back of the leg, which is why it’s so often confused with sciatica.
Unlike a true herniated disc, SI joint pain rarely travels below the knee. It also doesn’t typically cause numbness, tingling, or muscle weakness in the leg. Disc-related pain tends to follow a specific nerve path all the way into the foot, and larger herniations can cause reflex changes or actual weakness. SI joint pain is more diffuse and harder to pinpoint with a single finger.
The Quality of the Pain
Most people describe SI joint pain as a dull, aching sensation rather than a sharp or shooting one. It lacks the burning quality or pins-and-needles feeling that comes with nerve irritation. That said, it can flare into something sharper during certain movements, especially twisting, bending, or transitioning from one position to another. The baseline, though, is that deep, gnawing ache that sits in the low back and buttock and doesn’t let you get comfortable.
Movements and Positions That Make It Worse
SI joint pain is notoriously aggravated by transitional movements. Standing up from a chair, getting out of a car, rolling over in bed, and climbing stairs are some of the most common triggers. The joint bears a tremendous amount of load during single-leg activities, so walking up steps or standing on one leg can spike the pain noticeably.
Prolonged positions are just as problematic. Sitting for a long stretch, standing in one spot, or even sleeping on the affected side can all intensify the ache. The pattern is frustrating: both activity and stillness can make it worse, depending on the situation. Running, jumping, plyometrics, and contact sports load the joint heavily and tend to flare symptoms. So do repetitive motions and anything that shifts your weight unevenly onto one hip, like carrying a toddler or leaning to one side at a desk.
People with SI joint pain often notice they can’t find a comfortable position. They shift constantly in their chair, avoid crossing their legs, or favor one side when walking. That restless quality, the inability to settle, is one of the more distinctive everyday features.
Mechanical vs. Inflammatory SI Joint Pain
Not all SI joint pain behaves the same way, and the difference matters. Most cases are mechanical, meaning something about the joint’s alignment, movement, or surrounding ligaments is off. Mechanical SI pain tends to worsen with movement and improve with rest. It can start at any age, often has a more sudden onset tied to a specific injury or strain, and feels better when you’re lying still.
Inflammatory SI joint pain follows the opposite pattern. It’s associated with autoimmune conditions like ankylosing spondylitis or psoriatic arthritis, and it has a very specific fingerprint: it starts gradually before age 40, lasts longer than three months, gets worse with rest, and actually improves with exercise and movement. Night pain is a key feature. People with inflammatory sacroiliitis often wake in the second half of the night with deep stiffness and pain, then feel better once they get up and start moving. Morning stiffness lasting more than 30 minutes is another red flag.
If your SI joint pain follows that inflammatory pattern, especially the night pain and morning stiffness that loosens with activity, it’s worth pursuing further evaluation rather than assuming it’s a simple strain.
SI Joint Pain During Pregnancy
Pregnancy creates a perfect setup for SI joint problems. Your body produces a hormone that loosens the ligaments around the pelvis to prepare for delivery. This is helpful for childbirth but leaves the SI joint less stable than usual, making it vulnerable to shifting and irritation. The pain often shows up across one or both sides of the lower back, in the front of the pubic bone at hip level, and sometimes into the inner thighs.
Pregnant women with SI joint dysfunction often describe a feeling of weakness or instability in the pelvis, as if the bones might “give way.” This looseness also increases the risk of sprains and minor injuries. The pain typically worsens as pregnancy progresses and the load on the pelvis increases, then gradually improves after delivery as the ligaments tighten back up.
How It’s Distinguished From Other Back Pain
Because SI joint pain overlaps so heavily with other causes of low back pain, confirming it takes some detective work. A physical exam typically involves five specific stress tests that push, pull, or compress the SI joint from different angles. These include maneuvers where you lie on your back while a clinician pushes your knees apart, squeezes your hips together, or presses your bent knee toward the opposite shoulder. If three or more of these tests reproduce your familiar pain, SI joint dysfunction becomes a strong suspect.
The gold standard for confirmation is a diagnostic injection, where a numbing agent is placed directly into the joint under imaging guidance. If the injection reduces your pain by at least 75%, it confirms the SI joint as the source. Some evidence suggests that even 50% relief from a diagnostic block may be meaningful and can still guide treatment decisions.
The key sensory differences to keep in mind: disc herniations cause pain that follows a nerve root down into the lower leg or foot, often with numbness, tingling, or weakness. Facet joint pain in the lumbar spine tends to stay more centrally located and worsens with arching backward. SI joint pain stays in the buttock, low back, and upper leg, has that aching quality without nerve symptoms, and flares with the transitional movements and prolonged positions described above. That combination, deep one-sided ache plus pain with position changes plus no nerve symptoms below the knee, is the everyday signature of SI joint dysfunction.