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The sacroiliac joint (SI joint) is a strong joint between the bottom-most triangular bone of the spine, called the sacrum, and the ilium sections of the pelvis (the sections of the pelvis you put your hands on when you “put your hands on your hips”). The human body has two sacroiliac joints – one on the left and one on the right – that connect to the two ilium of the pelvis.
Based on movement, the SI joint can move slightly (typically from 3 to 7 degrees) to transfer weight and other forces from the upper body to the pelvis and legs, and vice-versa. Thus, the function of the SI joint is both shock absorption (depending on the amount of movement possible at the joint) as well as torque conversion, to transfer movement in the low body up to the spine.
The SI joints act a lot like the suspension system in a car – they absorb the body’s normal daily dose of steps, jolts and bumps, and provide stability. However, inflammation, normal wear and tear, or even a single incident or accident can damage the SI joint, affecting their slight normal movement and creating chronic and often debilitating low back pain. Causes of SI joint problems include injuries (e.g. a fall, car accident, or even a simple misstep); pregnancy (the ligaments that allow the SI joint to stretch during delivery may remain loose, post-pregnancy); anatomic variation (e.g. uneven leg length or scoliosis); and prior lumbar surgery (fusion of the lumbar spine changes its natural movement and ability to absorb shock).
When the strong ligaments of the SI joint become damaged, they may move excessively or insufficiently, causing inflammation and disrupting the joint and its surrounding nerves. When this happens, a person may feel pain in his/her low back, buttocks and/or legs, especially while walking, running, lifting or even sitting or lying down.
Common symptoms of SI joint dysfunction or inflammation include pain in the low back, buttocks and/or legs; pain or discomfort performing common daily activities that require the pelvis to pivot, like getting in and out of bed, walking up or down stairs or even turning in a chair; and difficulty sitting or lying down – especially if you experience an ache on one side of the body so painful it requires shifting weight to the other side to gain relief.
Diagnosis of SI joint dysfunction and/or inflammation can be challenging because the symptoms may mimic symptoms of problems in other parts of the body, such as with the lumbar region of the spine.
Typically, the consulting physician will ask about symptoms, medical history, and level of physical activity, and may conduct additional tests depending on the information provided. These tests may include a specific diagnostic protocol and manual provocative tests designed to gauge the scope and degree of sacroiliac pain as well as x-rays of the pelvis and low back, a CT scan or MRI scan. Additionally, the physician may also conduct tests based on joint injections or nerve blocks – drugs that temporarily block nerve signals from parts of the affected area to determine if pain originates in the SI joint.
While low back pain (LBP) affects up to 85% of all people at some point in life, 1,2 its underlying cause is often misunderstood. As a result, many patients seeking LBP relief do not receive the therapy they need. It has been reported that up to 30% of all chronic LBP is due to SI joint dysfunction. 3,4 However, patients with SI joint dysfunction may not be correctly diagnosed, leading to unnecessary treatment such as lumbar spine surgery. Additionally, the sacroiliac joint is the most likely source of low back pain after lumbar fusion. 5
1 Spoor AB, Oner FC (2013) Minimally Invasive Spine Surgery in Chronic Low Back Pain Patients. J Neurosurg Sci; Sep;57(3):203-18
2 Freburger JK et al. (2009) The Rising Prevalence of Chronic Low Back Pain. Arch Intern Med, 169(3):251-258
3 Simopoulos TT et al. (2012) A systematic Evaluation of Prevalence and Diagnostic Accuracy of Sacroiliac Joint Interventions. Pain Physician; 15:E305-E344
4 Cohen SP et al. (2013) Sacroiliac Joint Pain: A Comprehensive Review of Epidemiology, Diagnosis and Treatment. Expert Rev Neurother; 13(1):99-116
5 DePalma MJ et al. (2011) Etiology of Chronic Low Back Pain in Patients Having Undergone Lumbar Fusion. Pain Medicine; 12:732-739