In plain words
The sacroiliac joint, or SI joint, is where the base of the spine meets the pelvic bone on each side, at the back. The two SI joints, along with the joint at the front of the pelvis, form a ring that carries weight between the upper body and the legs. These joints move very little. In pregnancy, changes in load, posture, and hormones can make them sore, and pain there can spread to the low back, buttocks, or hips. This pain is part of . A clinician can check the joint and the pelvis by exam. Numbness, leg weakness, or loss of bladder or bowel control is an emergency, and that is a call to 911.
The deeper version
The pelvic ring transfers load between trunk and legs through three joints with very small physiological motion: the two sacroiliac joints, where the sacrum meets the ilia, and the pubic symphysis anteriorly. Movement at each sacroiliac joint is roughly 2 to 4 degrees of rotation, and at the symphysis roughly 1 to 2 millimeters of translation. European guidelines (Vleeming and colleagues, 2008) group sacroiliac and symphyseal pain under pelvic girdle pain. Diagnosis is clinical, using provocation tests such as the posterior pelvic pain provocation test, with imaging used to exclude other causes. Mechanical models of load transfer through the pelvic ring (Snijders and colleagues, 1993) suggest mechanisms, but evidence linking ligament laxity to pain is mixed. Controversy remains about whether sacroiliac and symphyseal pain share a mechanism.
Where it comes up
- Back, neck, and shoulder pain from feeding and carryingPostpartum: Your Body
- Pelvic girdle pain and SPDPregnancy: Your Body
What mothers here say about sacroiliac joint
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Sources
- Vleeming A, Albert HB, Ostgaard HC, et al. — European guidelines for the diagnosis and treatment of pelvic girdle pain. European Spine Journal (2008)
- Snijders CJ, Vleeming A, Stoeckart R — Transfer of lumbosacral load to iliac bones and legs. Clinical Biomechanics (1993)