Overview
Sacroiliitis is inflammation of the sacroiliac (SI) joint, which sits where your spine meets your pelvis. When the joint is irritated or inflamed, normal movement can feel painful and stiff, especially during weight transfer and walking. The discomfort often centers in the buttock and lower back and may spread into the hip or upper thigh. Depending on the cause, symptoms may improve with conservative care or may persist if an underlying inflammatory condition is present.
Symptoms
People with sacroiliitis commonly notice aching or sharp pain in the buttock or low back, often on one side. Pain may worsen with standing up from sitting, climbing stairs, walking for long periods, running, rolling over in bed, or standing on one leg. Some patients feel stiffness after rest and may have difficulty finding a comfortable position. In certain cases, the pain can radiate toward the hip or down the thigh, but true numbness and weakness are less typical unless another condition is involved.
Causes
Sacroiliitis can develop from inflammatory disorders that affect the joints, mechanical stress that overloads the SI joint, or less commonly infection or crystal-related inflammation. With mechanical causes, repeated strain and abnormal joint loading can irritate the joint lining and surrounding tissues. With inflammatory causes, the immune system drives persistent inflammation within the joint and adjacent bone. After pregnancy, childbirth-related pelvic changes, or a traumatic injury, the SI joint may also become irritated and inflamed.
Risk Factors
Risk can be higher if you have an inflammatory arthritis such as ankylosing spondylitis, psoriatic arthritis, or inflammatory bowel disease, particularly with a history of back stiffness. Recent or past pelvic or low-back injury, repetitive heavy lifting, and activities that place high stress on one side can increase risk. Pregnancy and postpartum periods can contribute due to pelvic ligament and joint changes, and factors like obesity and smoking may worsen mechanical loading and healing. A personal or family history of spondyloarthritis and HLA-B27 positivity can also raise the likelihood of inflammatory sacroiliitis.
Prevention
You can lower risk by strengthening the glutes and core, improving hip and pelvic mechanics, and maintaining good flexibility for the hips and lower back. Gradually increasing activity and avoiding sudden spikes in training or lifting reduces joint overload. Maintaining a healthy weight and using good lifting techniques can decrease repeated stress across the SI joint. If you have inflammatory arthritis, staying consistent with medical follow-up helps reduce flare-related joint inflammation.
How the Diagnosis Is Evaluated
Clinicians usually start with a detailed history focused on the pattern of buttock and low-back pain, morning stiffness, triggers, and any inflammatory or infection risk factors. A physical exam often includes SI joint provocation tests such as FABER, Gaenslen, thigh thrust, and compression/distraction maneuvers to see whether they reproduce your typical pain. Imaging may begin with X-ray to rule out other causes, but MRI is often used when inflammatory sacroiliitis is suspected or when symptoms persist. Blood tests like ESR and CRP may help when inflammation is suspected, and a diagnostic SI joint injection can sometimes confirm the pain source.
Nonsurgical Treatment Options
Treatment typically focuses on reducing inflammation and pain while restoring normal movement. Activity modification, heat or ice, and short-term use of anti-inflammatory medicines such as NSAIDs can help calm symptoms in many patients. Physical therapy is often central and may include exercises for core stability, glute strengthening, hip mobility, and gait or movement retraining to reduce SI joint stress. Some people benefit from an SI belt or targeted manual therapy techniques to improve pelvic support and comfort. If pain remains significant, an image-guided corticosteroid injection into the SI joint can reduce inflammation and improve function; some patients also use a carefully planned home exercise program afterward to maintain gains.
When to Seek Medical Attention
Seek prompt medical attention if you have fever, feel unwell, or have severe pain that rapidly worsens, since infection can occasionally mimic sacroiliitis. Get urgent care if you cannot bear weight, have new bowel or bladder problems, or develop progressive numbness, weakness, or loss of function. You should also seek timely evaluation if pain follows major trauma, if you have a history of cancer, or if you experience unexplained weight loss or persistent night pain. If symptoms do not improve after a reasonable trial of conservative care, or if stiffness suggests an inflammatory cause, schedule an evaluation to confirm the diagnosis and guide treatment.
Frequently Asked Questions
It usually feels like buttock and low-back pain near the sacrum that can worsen with standing, walking, stairs, or turning in bed.
Yes, pelvic and ligament changes during pregnancy and the postpartum period can irritate the SI joint in some people.
Most people improve with activity modification, physical therapy, NSAIDs when appropriate, and sometimes an image-guided corticosteroid injection.
Next Steps
If your pain matches the typical pattern of SI joint irritation, start with conservative measures like gentle activity, anti-inflammatory pain relief if safe for you, and a focused physical therapy plan. Arrange a clinical evaluation if symptoms are persistent, worsening, or accompanied by red flags such as fever or neurologic changes.