title: Morphological Distribution of the Anterior Inferior Iliac Spine in Patients With and Without Hip Impingement: Reliability, Validity, and Relationship to the Intraoperative Assessment.
abstract: BACKGROUND
  Subspinous impingement of the anterior inferior iliac spine (AIIS) on the femoral head-neck junction is increasingly recognized as a source of hip impingement. A classification system of AIIS morphology has previously been proposed that correlates with reduced hip motion and may predispose patients to subspinous hip impingement.
  
  
  OBJECTIVE
  To examine the morphological distribution of AIIS types in patients with and without diagnosed hip impingement and correlate AIIS morphology to intraoperative findings at the time of surgery.
  
  
  METHODS
  Cross-sectional study; Level of evidence, 3.
  
  
  METHODS
  Three-dimensional reconstructed pelvic computed tomography scans were generated for a stratified sample of 449 hips in patients without a history of hip pain or hip impingement and 59 hips in patients with a diagnosis of hip impingement. Three blinded assessors classified the AIIS for each hip twice. The morphological distribution between symptomatic and asymptomatic patients was compared, controlling for age, sex, and affected side. Within the symptomatic cohort, AIIS morphology was compared with the intraoperative assessment of a low-lying AIIS using the Fisher exact test.
  
  
  RESULTS
  The intraobserver reliability of the classification system in our cohort was substantial (κ = 0.68-0.77). The interobserver reliability was moderate (κ = 0.50). The morphological distribution between symptomatic and asymptomatic patients was similar, with 75% of patients in the asymptomatic group and 80% of the patients in the symptomatic group having a type 2 or type 3 AIIS. When matched for age, sex, and affected side, there was no significant difference in the assessed classification type between the groups ( P = .55). Within the symptomatic group, there was no significant correlation between the surgeon assessment of a low-lying AIIS and a type 2 or type 3 radiographic classification ( P = .10). The positive predictive value of a type 2 or type 3 AIIS classification for hip impingement symptoms was 10%, and the negative predictive value was 91%.
  
  
  CONCLUSIONS
  These findings suggest that a high percentage of patients with AIIS morphology associated with subspinous impingement are, in fact, asymptomatic. The current radiographic classification scheme should not be used exclusively for clinical decision making.
authors.affiliation: Department of Orthopaedics, Walter Reed National Military Medical Center, Bethesda, Maryland, USA.
authors.forename: George C
authors.initials: GC
authors.lastname: Balazs
authors.affiliation: Department of Radiology, Walter Reed National Military Medical Center, Bethesda, Maryland, USA.
authors.forename: Benjamin C
authors.initials: BC
authors.lastname: Williams
authors.affiliation: Department of Radiology, Walter Reed National Military Medical Center, Bethesda, Maryland, USA.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Knaus
authors.affiliation: Department of Research Programs, Walter Reed National Military Medical Center, Bethesda, Maryland, USA.
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Brooks
authors.affiliation: Department of Orthopaedics, Walter Reed National Military Medical Center, Bethesda, Maryland, USA.
authors.forename: Jonathan F
authors.initials: JF
authors.lastname: Dickens
authors.affiliation: Department of Orthopaedics, Walter Reed National Military Medical Center, Bethesda, Maryland, USA.
authors.forename: Michael P
authors.initials: MP
authors.lastname: McCabe
authors.affiliation: Department of Orthopaedics, Walter Reed National Military Medical Center, Bethesda, Maryland, USA.
authors.forename: Terrence D
authors.initials: TD
authors.lastname: Anderson
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D057925:Femoracetabular Impingement / Q000473:pathology*; D005270:Femur Head / Q000473:pathology; D005272:Femur Neck / Q000473:pathology; D006621:Hip Joint / Q000601:surgery*; D006801:Humans; D007085:Ilium / Q000033:anatomy & histology / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed; D055815:Young Adult
keywords: anterior inferior iliac spine; femoroacetabular impingement; subspinous hip impingement