Cam-type femoroacetabular impingement—correlations between alpha angle versus volumetric measurements and surgical findings

  • Riham Dessouky
  • Avneesh Chhabra
  • Lihua Zhang
  • Adam Gleason
  • Rajiv Chopra
  • Yonatan Chatzinoff
  • Nicholas P. Fey
  • Yin Xi
  • Joel WellsEmail author



Determine correlations of 3DCT cam-type femoroacetabular impingement (FAI) measurements with surgical findings of labral tear and cartilage loss.


Digital search of symptomatic cam-type FAI from July 2013 to August 2016 yielded 43 patients. Two readers calculated volumes of femoral head, bump, and alpha angles on 3DCT images. Correlations between CT and surgical findings, inter-, and intra-reader reliabilities were assessed using Spearman rank correlation and intraclass correlation coefficients (ICC).


Thirteen men and 14 women aged 37 ± 10 (mean ± SD) years were included. Most common clinical finding was positive flexion–adduction–internal rotation (70.4%). Twenty-seven labral tears and 20 cartilage defects were surgically detected. Significant correlations existed between femoral bump, head volumes, and extent of the labral tear (p = 0.008 and 0.003). No significant correlations were found between the alpha angles at 12 to 3 o’clock and the extent of labral tear (p = 0.2, 0.8, 0.9, and 0.09) or any measurement with the cartilage loss (p values for alpha 12 to 3, bump, and head volumes = 0.7, 0.3, 0.9, 0.9, 0.07, and 0.2). Inter- and intra-reader reliabilities were excellent to moderate for femoral head and bump volumes (ICC = 0.85, 0.52, and 0.8, 0.5) and moderate to poor for alpha angles (ICC = 0.48, 0.40, 0.05, 0.25 and 0.3, 0.24, 0.29, 0.49).


Three dimensional volumetric measurements of cam-type FAI significantly correlate with the extent of intraoperative labral tears. Superior inter- and intra-reader reliability to that of alpha angles renders it a more clinically relevant measurement for quantifying cam morphology.

Key Points

• The 3DCT bump volume and femoral head volume showed significant correlations with the extent of labral tear (p values = 0.008 and 0.003).

• No significant correlations were seen between alpha angles and the extent of labral tear (p values > 0.05).

• Inter- and intra-reader reliability was excellent to moderate (ICC = 0.85 and 0.52, 0.8, and 0.5) for femoral head and bump volumes while inter- and intra-reader reliability was fair to poor (ICC = 0.48, 0.40, 0.05, 0.25 and 0.3, 0.24, 0.29, 0.49) for alpha angles.


Hip joint Femoroacetabular impingement Image processing Computer-assisted Tomography 



Three-dimensional computed tomography


Flexion-abduction-external rotation


Flexion-adduction-internal rotation


Femoroacetabular impingement



The authors state that this work has not received any funding.

Compliance with ethical standards


The scientific guarantor of this publication is Avneesh Chhabra, MD.

Conflict of interest

The authors of this manuscript declare relationships with the following companies:

RD, LZ, AG, RC, YC, NPF: no conflicts of interest.

AC: consultant ICON Medical, royalties: Jaypee, Wolters (not related).

Statistics and biometry

One of the authors has significant statistical expertise.

Informed consent

Written informed consent was waived by the Institutional Review Board.

Ethical approval

Institutional Review Board approval was obtained.


• retrospective

• cross-sectional study

• performed at one institution

Supplementary material

330_2018_5968_MOESM1_ESM.docx (21 kb)
ESM 1 (DOCX 21 kb)


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Copyright information

© European Society of Radiology 2019

Authors and Affiliations

  1. 1.Department of Radiology, Zagazig University Hospitals and Faculty of MedicineZagazig UniversityZagazigEgypt
  2. 2.Department of RadiologyUniversity of Texas Southwestern Medical CenterDallasUSA
  3. 3.Department of Orthopedic SurgeryUniversity of Texas Southwestern Medical CenterDallasUSA
  4. 4.Advanced Imaging Research CenterUniversity of Texas Southwestern Medical CenterDallasUSA
  5. 5.Departments of Bioengineering and Mechanical EngineeringThe University of Texas at DallasRichardsonUSA
  6. 6.Department of Physical Medicine and RehabilitationUniversity of Texas Southwestern Medical CenterDallasUSA

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