Advertisement

Clinical Orthopaedics and Related Research

, Volume 467, Issue 3, pp 660–665 | Cite as

Comparison of MRI Alpha Angle Measurement Planes in Femoroacetabular Impingement

  • Kawan S. RakhraEmail author
  • Adnan M. Sheikh
  • David Allen
  • Paul E. Beaulé
Symposium: Femoroacetabular Impingement: Current Status of Diagnosis and Treatment

Abstract

Insufficient femoral head-neck offset is common in femoroacetabular impingement (FAI) and reflected by the alpha angle, a validated measurement for quantifying this anatomic deformity in patients with FAI. We compared the alpha angle determined on magnetic resonance imaging (MRI) oblique axial plane images with the maximal alpha angle value obtained using radial images. The MRIs of 41 subjects with clinically suspected FAI were reviewed and alpha angle measurements were performed on both oblique axial plane images parallel to the long axis of the femoral neck and radial images obtained using the center of the femoral neck as the axis of rotation. The mean oblique axial plane and mean maximal radial alpha angle values were 53.4° and 70.5°, respectively. In 54% of subjects, the alpha angle was less than 55° on the conventional oblique axial plane image but 55° or greater on the radial plane images. Radial images yielded higher alpha angle values than oblique axial images. Patients with clinically suspected FAI may have a substantial contour abnormality that can be underestimated or missed if only oblique axial plane images are reviewed. Radial plane imaging should be considered in the MRI investigation of FAI.

Level of Evidence: Level III, diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Keywords

Alpha Angle Magnetic Resonance Arthrography Femoroacetabular Impingement Radial Plane Anatomic Deformity 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgments

We thank Anna Fazekas and Simon Dagenais for assistance in study design and statistical analysis and Natasha La Russa for postprocessing reformations of the MRI studies.

References

  1. 1.
    Beaulé P, Zaragoza E, Motamedi E, Copelan N, Dorey F. Three-dimensional computed tomography of the hip in the assessment of femoroacetabular impingement. J Orthop Res. 2005;23:1286–1292.PubMedGoogle Scholar
  2. 2.
    Beck M, Kalhor M, Leunig M, Ganz R. Hip morphology influences the pattern of damage to the acetabular cartilage. J Bone Joint Surg Br. 2005;87:1012–1018.PubMedCrossRefGoogle Scholar
  3. 3.
    Ganz R, Leunig M, Leunig-Ganz K, Harris WH. The etiology of osteoarthritis of the hip: an integrated mechanical concept. Clin Orthop Relat Res. 2008;466:264–272.PubMedCrossRefGoogle Scholar
  4. 4.
    Ganz R, Parvizi J, Beck M, Leunig M, Nötzli H, Siebenrock KA. Femoroacetabular impingement: a cause for osteoarthritis of the hip. Clin Orthop Relat Res. 2003;417:112–120.PubMedGoogle Scholar
  5. 5.
    Ito K, Minka KA, Leunig M, Werlen S, Ganz R. Femoroacetabular impingement and the cam-effect: a MRI-based quantitative anatomical study of the femoral head-neck offset. J Bone Joint Surg Br. 2001;83:171–176.PubMedCrossRefGoogle Scholar
  6. 6.
    James SLJ, Ali K, Malara F, Young D, O’Donnell J, Connell DA. MRI findings of femoroacetabular impingement. AJR Am J Roentgenol. 2006;187:1412–1419.PubMedCrossRefGoogle Scholar
  7. 7.
    Kassarjian A, Yoon LS, Belzile E, Connolly SA, Millis MB, Palmer WE. Triad of MR arthrographic findings in patients with cam-type femoroacetabular impingement. Radiology. 2005;236:588–592.PubMedCrossRefGoogle Scholar
  8. 8.
    Meyer DC, Beck M, Ellis T, Ganz R, Leunig M. Comparison of six radiographic projections to assess femoral head/neck asphericity. Clin Orthop Relat Res. 2006;445:181–185.PubMedGoogle Scholar
  9. 9.
    Nötzli HP, Wyss TF, Stoecklin CH, Schmid MR, Treiber K, Hodler J. The contour of the femoral head-neck junction as a predictor for the risk of anterior impingement. J Bone Joint Surg Br. 2002;84:556–560.PubMedCrossRefGoogle Scholar
  10. 10.
    Pfirrmann CWA, Mengiardi B, Dora C, Kalberer F, Zanetti M, Hodler J. Cam and pincer Femoroacetabular impingement: characteristic MR arthrographic findings in 50 patients. Radiology. 2006;240:778–785.PubMedCrossRefGoogle Scholar
  11. 11.
    Siebenrock KA, Wahab KHA, Werlen S, Kalhor M, Leunig M, Ganz R. Abnormal extension of the femoral head epiphysis as a cause of cam impingement. Clin Orthop Relat Res. 2004;418:54–60.PubMedCrossRefGoogle Scholar
  12. 12.
    Tannast M, Sienbenrock KA, Anderson SE. Femoroacetabular impingement: radiographic diagnosis—what the radiologist should know. AJR Am J Roentgenol. 2007;188:1540–1552.PubMedCrossRefGoogle Scholar

Copyright information

© The Association of Bone and Joint Surgeons 2008

Authors and Affiliations

  • Kawan S. Rakhra
    • 1
    Email author
  • Adnan M. Sheikh
    • 1
  • David Allen
    • 2
  • Paul E. Beaulé
    • 2
  1. 1.Department of Diagnostic ImagingThe Ottawa Hospital—General Campus, University of OttawaOttawaCanada
  2. 2.Division of Orthopaedic Surgery, The Ottawa Hospital University of OttawaOttawaCanada

Personalised recommendations