Cam and pincer femoroacetabular impingement: CT findings of features resembling femoroacetabular impingement in a young population without symptoms

AJR Am J Roentgenol. 2013 Feb;200(2):389-95. doi: 10.2214/AJR.12.8546.


Objective: The purpose of this study was to use CT to determine the presence of radiologic parameters associated with cam and pincer femoroacetabular impingement (FAI) in a young population without symptoms.

Materials and methods: A retrospective review of 50 patients (age range, 20-40 years) with no current or previous hip disorder who underwent CT of the abdomen and pelvis was conducted. Multiplanar images were reformatted with a soft-tissue and bone algorithm and assessed for the presence of parameters associated with FAI; alpha angle greater than 55°, femoral head-neck offset less than 8 mm, angle of acetabular version less than 15°, lateral center edge angle greater than 40°, acetabular index less than 0°, pistol-grip deformity, acetabular crossover, and prominent posterior wall signs.

Results: At least one abnormal parameter was present in 66% of joints, and two or more abnormal parameters were present in 29% of joints. In seven patients the findings were bilateral. Parameters of mixed morphologic characteristics (cam and pincer) were found in 22% of joints. In side-by-side comparison, high alpha angles were seen in 36 joints measured in the radial plane compared with only three joints measured in the axial oblique plane.

Conclusion: The CT finding of FAI-like features was made with high frequency in a young symptom-free population. Cutoff values for defining morphologic abnormalities associated with FAI may have been set too low in the current literature. Alpha angle measurements in the radial plane may be a more accurate quantitative assessment of asphericity of the femoral head-neck junction than are measurements in the axial oblique plane.

MeSH terms

  • Adult
  • Algorithms
  • Female
  • Femoracetabular Impingement / diagnostic imaging*
  • Humans
  • Male
  • Radiographic Image Interpretation, Computer-Assisted
  • Reproducibility of Results
  • Retrospective Studies
  • Tomography, X-Ray Computed / methods*