title: Reliability of a new hip lateral view to quantify alpha angle in femoroacetabular impingement.
abstract: BACKGROUND
  Radiographic measurement of the alpha angle (AA) in femoroacetabular impingement (FAI) is not well codified and invasive techniques such as MR- or CT-arthrography remain the gold standard. Excessive acetabular coverage described in pincer-type FAI can be seen on plain radiographs but has never been quantified and anterior center edge (ACE) angle, described on the false-profile view (FP) to measure anterior acetabular coverage has never been evaluated in FAI.
  
  
  OBJECTIVE
  In this study we wanted to determine if a plain radiograph could efficiently measure AA compared to CT-arthrography and if ACE could quantify the acetabular coverage in FAI.
  
  
  METHODS
  We developed a hip view combining a lateral view and a FP, called profile view in impingement position (PIP). Twenty-six patients operated for FAI had CT-arthrography, PIP and FP. Nineteen control subjects had the PIP. AA were measured twice by three raters and ACE once. We compared AA measured on patients between CT and PIP, on PIP between patients and controls, ACE measured on patients between PIP and FP, and did a reproducibility analysis. Means were compared by paired or unpaired t-tests; reproducibility was measured by intraclass correlation coefficient (ICC).
  
  
  RESULTS
  Mean AA was 65.8° (range, 48-85°) on CT-arthrography and 63.9° (range, 50-87°) on PIP (P>0.05). ICC for PIP measures were 0.8-0.9 for intra-rater and 0.6-0.9 for inter-rater reliability. Mean AA on PIP in patients was 63.3° (range, 52-87°) and 44.9° (range, 34-67°) in controls (P<0.001). Mean ACE was 26.8° (range, 14-41°) on PIP and 32.8° (range, 18-56°) on the FP (P=0.015).
  
  
  CONCLUSIONS
  The PIP is a reliable view to measure the AA in FAI as measures on PIP and CT-arthrography were not significantly different with a good reproducibility. All of the painful hips and 2 controls had an AA>50°. PIP was not efficient to measure ACE.
  
  
  METHODS
  Level III, case-control study.
authors.affiliation: Clinique chirurgicale orthopédique et traumatologique, CHU hôtel-Dieu Nantes, 1, place Alexis-Ricordeau, 44093 Nantes cedex 1, France. Electronic address: guillaumeanthony.odri@chu-nantes.fr.
authors.forename: G-A
authors.initials: GA
authors.lastname: Odri
authors.affiliation: Clinique chirurgicale orthopédique et traumatologique, CHU hôtel-Dieu Nantes, 1, place Alexis-Ricordeau, 44093 Nantes cedex 1, France.
authors.forename: R
authors.initials: R
authors.lastname: Frioux
authors.affiliation: Service de radiologie centrale, CHU hôtel-Dieu Nantes, 44093 Nantes, France.
authors.forename: H
authors.initials: H
authors.lastname: Redon
authors.affiliation: Clinique chirurgicale orthopédique et traumatologique, CHU hôtel-Dieu Nantes, 1, place Alexis-Ricordeau, 44093 Nantes cedex 1, France.
authors.forename: N
authors.initials: N
authors.lastname: Fraquet
authors.affiliation: Service de radiologie centrale, CHU hôtel-Dieu Nantes, 44093 Nantes, France.
authors.forename: A
authors.initials: A
authors.lastname: Bertrand-Vasseur
authors.affiliation: IRIS GRIM, clinique Brétéché, 27, rue de la Béraudière, 44000 Nantes, France.
authors.forename: J
authors.initials: J
authors.lastname: Isnard
authors.affiliation: Clinique chirurgicale orthopédique et traumatologique, CHU hôtel-Dieu Nantes, 1, place Alexis-Ricordeau, 44093 Nantes cedex 1, France.
authors.forename: F
authors.initials: F
authors.lastname: Gouin
mesh_terms: D000293:Adolescent; D000328:Adult; D001175:Arthrography; D005260:Female; D057925:Femoracetabular Impingement / Q000000981:diagnostic imaging*; D006621:Hip Joint / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed; D055815:Young Adult
keywords: Alpha angle; Anterior center edge angle; CT-arthrography; Femoroacetabular impingement; Reliability; Reproducibility