Summary Sacroiliac (SI) dislocations and crescent fractures include a spectrum of injuries involving the pelvis which can lead to instability and pelvic malalignment. Diagnosis requires pelvic radiographs with CT scan. Treatment is generally operative with reduction and fixation of both the anterior and posterior pelvis ring as needed. Epidemiology Spectrum of injuries that include incomplete (Sacroiliac) SI dislocation posterior SI ligaments remain intact rotationally unstable complete SI dislocations posterior SI ligaments ruptured vertically and rotationally unstable SI fracture-dislocation (crescent fracture) iliac wing fracture that enters the SI joint injury to posterior ligaments vary combination of vertical iliac fx and SI dislocation posterior ilium remains attached to sacrum by posterior SI ligaments anterior ilium dislocates from sacrum with internal rotation deformity when ilium fragment remains with sacrum it is termed a crescent fracture Pathophysiology Mechanism of injury lateral compression force usually high energy Pathoanatomy degree of injury to posterior structures determines pelvic stability Iliac wing fractures may be associated with open wounds and may involve bowel entrapment Anatomy Ligaments the SI joint is stabilized by the posterior pelvic ligaments sacrospinous sacrotuberous anterior sacroiliac posterior sacroiliac Nerves the L5 nerve root crosses the sacral ala approximately 2 cm medial to SI joint Blood supply the superior gluteal artery runs across SI joint exits pelvis via greater sciatic notch Classification No classification system specifically for SI injury included in Young- Burgess and Tile classification of pelvic fractures crescent fractures described as LC-2 injury according to Young-Burgess Presentation Symptoms pelvic pain Physical Exam assess hemodynamic status perform detailed neurological exam abdominal assessment to look for distention rectal exam examine urethral meatus for blood Imaging Radiographs recommended views AP pelvis inlet and outlet views CT scan evaluation of sacral fractures posterior pelvis better delineated Treatment Operative immediate skeletal traction indications login to view 1 more bullet anterior ring ORIF indications login to view 1 more bullet anterior and posterior ring ORIF indications login to view 2 more bullets ORIF of ilium indications login to view 2 more bullets Techniques Closed Reduction and Percutaneous Fixation positioning intraoperative traction may aid in reduction small midline bump under sacrum may assist with SI screw placement imaging inlet view login to view 1 more bullet outlet view login to view 1 more bullet lateral sacral view login to view 1 more bullet complications L5 nerve root at risk with anterior perforation of iliosacral screw as nerve goes inferiorly over sacral ala ORIF approach anterior approach login to view 1 more bullet posterior approach login to view 1 more bullet fixation plates iliosacral lag screws (SI screws) Complications DVT 35%-50% Neurological injury Loss of reduction and failure of fixation Prognosis Primarily based on accurate and stable reduction of SI joint