sacroiliaca

The sacroiliaca, or sacroiliac joints, are the paired joints between the sacrum and the ilium on each side of the pelvis. They function to transfer weight from the axial skeleton to the lower limbs and to stabilize the pelvic ring.

Anatomy and structure: Each sacroiliac joint comprises two components. The anterior part is a diarthrodial (synovial) joint with limited but present mobility, while the posterior part functions mainly as a syndesmosis reinforced by strong ligaments. The interlocking, irregular articular surfaces are covered by hyaline cartilage and a joint capsule surrounds the synovial portion. Key ligaments include the anterior and posterior sacroiliac ligaments and the interosseous sacroiliac ligament, which provides most of the joint’s stability. The sacrospinous and sacrotuberous ligaments contribute to pelvic stability and help to shape the pelvic outlet. The iliolumbar ligament links the ilium to the lumbar spine and supports the lumbosacral junction.

Biomechanics: Mobility at the sacroiliac joints is limited but functionally important, enabling small gliding and rotational movements such as nutation and counternutation during activities like walking and bending. The joints are designed to transmit large axial loads from the spine to the pelvis and legs, with stability augmented by surrounding ligaments and the pelvic ring. Hormonal and mechanical factors can increase laxity during pregnancy, altering SI joint mechanics.

Clinical relevance: Sacroiliac joint dysfunction and sacroiliitis are common sources of low back and buttock pain. Diagnosis may involve clinical testing and imaging (X-ray, CT, MRI). Treatments include physical therapy, stabilization exercises, injections of local anesthetics or corticosteroids, and, in refractory cases, sacroiliac joint fusion.

The term sacroiliaca refers to the two sacroiliac joints that unite the sacrum with the ilia.