Stephen J. Schueler, M.D.

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Sacroiliac Injury Anatomy

To better understand SI joint injury, it helps to understand the anatomy of the lower back and pelvis.

The pelvis supports the spinal column from above. From below, it provides the hip joints for both legs.

The sacrum is part of the pelvis, while the coccyx is the lowest part of the spine. The sacroiliac joint (SI joint) refers to the semi-rigid joint between the sacrum and the ileum or bony pelvis. This joint, like others, is stabilized by ligaments and muscles. Unlike most other joints, it has almost no motion.

Anatomy examples:

  • Bones and ligaments of the pelvis
  • Sacrum and coccyx
  • Sacroiliac joint of the pelvis
  • Major blood vessels of the pelvis:

Last Updated: Jul 13, 2009 References
Authors: Stephen J. Schueler, MD; John H. Beckett, MD; D. Scott Gettings, MD
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PubMed Sacroiliac Injury References
  1. Borrelli J Jr, Koval KJ, Helfet DL. Operative stabilization of fracture dislocations of the sacroiliac joint. Clin Orthop Relat Res. 1996 Aug;(329):141-6. [8769445]
  2. Major NM, Helms CA. Pelvic stress injuries: the relationship between osteitis pubis (symphysis pubis stress injury) and sacroiliac abnormalities in athletes. Skeletal Radiol. 1997 Dec;26(12):711-7. [9453104]
  3. Stevens KJ, Preston BJ, Hahn DM.Bilateral fracture dislocation of the sacroiliac joint. Skeletal Radiol. 1997 Sep;26(9):556-8. [9342818]
  4. Wright V, Zelle BA, Prayson M. Bilateral sacroiliac joint dislocation without associated fracture or anterior pelvic ring injuries. J Orthop Trauma. 2004 Oct;18(9):634-7. [15448454]
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