title: Associations between Alpha Angle and Herniation Pit on MRI Revisited in 185 Asymptomatic Hip Joints.
abstract: OBJECTIVE
  To evaluate the association between alpha angle and herniation pit on MRI in asymptomatic hip joints and their associations with demographic variables.
  
  
  METHODS
  Hip MRI of 185 asymptomatic hip joints of 105 adults (age 18 to 80 years) from September 2011 through December 2012 were retrospectively studied. Alpha angles were measured on oblique axial MR images by 2 observers. Herniation pit was determined by 1 observer. Size measures, prevalence, and statistical analyses were conducted regarding its association with age, gender, laterality (right or left hip). Intra- and inter-observer agreements were determined by intra-class correlation coefficient.
  
  
  RESULTS
  The prevalence of herniation pit in asymptomatic hips was 21.6%. The range of alpha angle was 27.6-65.0 degrees. Seventeen and 16 out of 185 (9.1% and 8.6%) hip joints showed alpha angle of ≥ 55 degrees in first and second measurement sessions, respectively. There was no association between alpha angle ≥ 55 and presence of herniation pit. There was no association between alpha angle ≥ 55 and the size of herniation pit. Inter-observer agreement of alpha angle was 0.485 between first measurements of first vs. second observer, respectively. Intra-observer agreement of alpha angle was 0.654, respectively. Forty (21.6%) of 185 hip joints (35 of 105 patients, 33.3%) had herniation pit, with no difference according to age, gender, or laterality of hip joint.
  
  
  CONCLUSIONS
  There is no association between alpha angle ≥ 55 degrees and presence of herniation pit or demographic variables.
authors.affiliation: Department of Radiology, Seoul National University Bundang Hospital, Seongnam 13620, Korea.
authors.forename: Eunchae
authors.initials: E
authors.lastname: Lee
authors.affiliation: Department of Radiology, Seoul National University Bundang Hospital, Seongnam 13620, Korea. ; Department of Radiology, Hallym University Dongtan Sacred Heart Hospital, Hwaseong 18450, Korea.
authors.forename: Jung-Ah
authors.initials: JA
authors.lastname: Choi
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D058070:Asymptomatic Diseases; D005260:Female; D005272:Femur Neck / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D006621:Hip Joint / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011859:Radiography; D012189:Retrospective Studies; D055815:Young Adult
keywords: Alpha angle; Herniation pit; Hip; MRI