Clinical Orthopaedics and Related Research®

, Volume 473, Issue 4, pp 1289–1296 | Cite as

Patient-Specific Anatomical and Functional Parameters Provide New Insights into the Pathomechanism of Cam FAI

  • K. C. Geoffrey Ng
  • Mario Lamontagne
  • Andrew P. Adamczyk
  • Kawan S. Rahkra
  • Paul E. BeauléEmail author
Symposium: 2014 Bernese Hip Symposium



Femoroacetabular impingement (FAI) represents a constellation of anatomical and clinical features, but definitive diagnosis is often difficult. The high prevalence of cam deformity of the femoral head in the asymptomatic population as well as clinical factors leading to the onset of symptoms raises questions as to what other factors increase the risk of cartilage damage and hip pain.


The purpose was to identify any differences in anatomical parameters and squat kinematics among symptomatic, asymptomatic, and control individuals and if these parameters can determine individuals at risk of developing symptoms of cam FAI.


Forty-three participants (n = 43) were recruited and divided into three groups: symptomatic (12), asymptomatic (17), and control (14). Symptomatic participants presented a cam deformity (identified by an elevated alpha angle on CT images), pain symptoms, clinical signs, and were scheduled for surgery. The other recruited volunteers were blinded and unaware whether they had a cam deformity. After the CT data were assessed for an elevated alpha angle, participants with a cam deformity but who did not demonstrate any clinical signs or symptoms were considered asymptomatic, whereas participants without a cam deformity and without clinical signs or symptoms were considered healthy control subjects. For each participant, anatomical CT parameters (axial alpha angle, radial alpha angle, femoral head-neck offset, femoral neck-shaft angle, medial proximal femoral angle, femoral torsion, acetabular version) were evaluated. Functional squat parameters (maximal squat depth, pelvic range of motion) were determined using a motion capture system. A stepwise discriminant function analysis was used to determine which of the parameters were most suitable to classify each participant with their respective subgroup.


The symptomatic group showed elevated alpha angles and lower femoral neck-shaft angles, whereas the asymptomatic group showed elevated alpha angles in comparison with the control group. The best discriminating parameters to determine symptoms were radial alpha angle, femoral neck-shaft angle, and pelvic range of motion (p < 0.001).


In the presence of a cam deformity, indications of a decreased femoral neck-shaft angle and reduced pelvic range of motion can identify those at risk of symptomatic FAI.

Level of Evidence

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


Femoral Head Discriminant Function Analysis Alpha Angle Symptomatic Group Asymptomatic Group 
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.



We thank Kevin Dwyer and Giulia Mantovani, from the University of Ottawa’s Human Movement Biomechanics Laboratory, for their help with data collection and processing. We also thank Jae-Jin Ryu and Gillian Parker, from The Ottawa Hospital’s Division of Orthopedic Surgery, for their help with patient recruitment and data collection.

Supplementary material

11999_2014_3797_MOESM1_ESM.pdf (331 kb)
Supplementary material 1 (PDF 331 kb)


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Copyright information

© The Association of Bone and Joint Surgeons® 2014

Authors and Affiliations

  • K. C. Geoffrey Ng
    • 1
  • Mario Lamontagne
    • 1
    • 2
  • Andrew P. Adamczyk
    • 3
  • Kawan S. Rahkra
    • 4
  • Paul E. Beaulé
    • 5
    Email author
  1. 1.Department of Mechanical EngineeringUniversity of OttawaOttawaCanada
  2. 2.School of Human KineticsUniversity of OttawaOttawaCanada
  3. 3.Faculty of MedicineUniversity of OttawaOttawaCanada
  4. 4.Department of Diagnostic RadiologyUniversity of OttawaOttawaCanada
  5. 5.Division of Orthopaedic SurgeryUniversity of OttawaOttawaCanada

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