title: Transverse morphology of the sacroiliac joint: effect of angulation and implications for fluoroscopically guided sacroiliac joint injection.
abstract: OBJECTIVE
  Effects of angulation of computed tomography (CT) reconstruction plane on sacroiliac (SI) joint morphology were studied, and factors influencing the approach to fluoroscopically guided SI joint injection were assessed.
  
  
  METHODS
  CT scans of pelvises were reformatted on 41 subjects, aged 51.7 (+/-15.1) years. Transverse images were reconstructed at the caudal 3 cm of the SI joint tilting plane of reconstruction from -30 degrees to +30 degrees at 15 degrees increments. Anteroposterior diameter of joint (depth), angle from sagittal plane (orientation angle), and distance from skin were measured. Joint contour was classified, and presence of bone blocking access to the joint was recorded. Comparison between angles were analysed by t-test. Relationships between variables were assessed by a Pearson correlation test.
  
  
  RESULTS
  Depth was shorter with angulation in the inferior direction (P<0.01). Orientation angle increased with superior angulation (P<0.01). Distance from skin increased (P<0.01) with angulation in either direction. Joint contour was significantly different from baseline at each angle (P<0.001) but highly variable. Inferior angulation resulted in interposition of ilium between skin and SI joint, and superior angulation caused bone block due to the lower sacrum. None of these features was identified without tilting of the reconstruction plane, and effects were more pronounced with steeper angulation.
  
  
  CONCLUSIONS
  Angulation of the reconstruction plane considerably affects the appearance of the sacroiliac joints. By shortening joint depth, an inferiorly directed approach to SI joint injection may make fluoroscopic guidance easier, although associated bony interposition can prevent access to the synovial compartment. A superiorly directed approach is more likely to have adverse effects.
authors.affiliation: Department of Radiology and Diagnostic Imaging, University of Alberta Hospital, 2A2.41 Walter C. Mackenzie Centre, 8440-112 Street, Edmonton, Alberta, T6G 2B7, Canada.
authors.forename: Bernice C
authors.initials: BC
authors.lastname: Ling
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Lee
authors.forename: H S Jeffrey
authors.initials: HS
authors.lastname: Man
authors.forename: Gian S
authors.initials: GS
authors.lastname: Jhangri
authors.forename: Michael G A
authors.initials: MG
authors.lastname: Grace
authors.forename: Robert G W
authors.initials: RG
authors.lastname: Lambert
mesh_terms: D000779:Anesthetics, Local / Q000008:administration & dosage; D018771:Arthralgia / Q000000981:diagnostic imaging*; D016477:Artifacts; D005260:Female; D006801:Humans; D007270:Injections, Intra-Articular / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011856:Radiographic Image Enhancement / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012446:Sacroiliac Joint / Q000000981:diagnostic imaging*; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D000779:Anesthetics, Local