title: Posterior iliac offset: description of a new radiological measurement of sacroiliac joint instability.
abstract: The purpose of this study was to describe the radiological characteristics of a previously unreported finding: posterior iliac offset at the sacroiliac joint and to assess its association with pelvic instability as measured by initial displacement and early implant loosening or failure. Radiographs from 42 consecutive patients with a mean age of 42 years (18 to 77; 38 men, four women) and mean follow-up of 38 months (3 to 96) with Anteroposterior Compression II injuries, were retrospectively reviewed. Standardised measurements were recorded for the extent of any diastasis of the pubic symphysis, widening of the sacroiliac joint, static vertical ramus offset and a novel measurement (posterior offset of the ilium at the sacroiliac joint identified on axial CT scan). Pelvic fractures with posterior iliac offset exhibited greater levels of initial displacement of the anterior pelvis (anterior sacroiliac widening, pubic symphysis diastasis and static vertical ramus offset, p < 0.001,0.034 and 0.028, respectively). Pelvic fractures with posterior ilium offset also demonstrated higher rates of implant loosening regardless of fixation method (p = 0.05). Posterior offset of the ilium was found to be a reliable and reproducible measurement with substantial inter-observer agreement (kappa = 0.70). Posterior offset of the ilium on axial CT scan is associated with greater levels of initial pelvic displacement and early implant loosening.
authors.affiliation: UT Medical Center, Department of Orthopaedic Surgery, Professional Building F, 1926 Alcon Highway, Suite 210, Knoxville, Tennessee, 37920, USA.
authors.forename: B M
authors.initials: BM
authors.lastname: Tonne
authors.affiliation: Methodist Hospital, Department of Orthopaedic Surgery, Indiana University Health, 46202, USA.
authors.forename: L B
authors.initials: LB
authors.lastname: Kempton
authors.affiliation: Loyola University Medical Center, 2160 S. First Avenue Maywood, Illinois, 60153, USA.
authors.forename: W D
authors.initials: WD
authors.lastname: Lack
authors.affiliation: Carolinas Medical Center, Department of Orthopaedic Surgery, 1025 Morehead Medical Drive, Charlotte, North Carolina 28204, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Karunakar
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D005500:Follow-Up Studies; D005593:Fracture Fixation, Internal / Q000379:methods; D050723:Fractures, Bone / Q000150:complications* / Q000000981:diagnostic imaging / Q000601:surgery; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging* / Q000209:etiology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D012189:Retrospective Studies; D012446:Sacroiliac Joint / Q000000981:diagnostic imaging* / Q000293:injuries; D014057:Tomography, X-Ray Computed; D055815:Young Adult
keywords: Pelvic posterior shift; Anteroposterior compression; Pelvic ring injury classification