Femoroacetabular Hip Impingement Syndrome

Radiology Corner

Femoroacetabular Hip Impingement Syndrome

Alicia M. Yochum RN, DC, DACBR

Published: September 2017

Journal of the Academy of Chiropractic Orthopedists

September 2017, Volume 14, Issue 3

This is an Open Access article which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The article copyright belongs to the author and the Academy of Chiropractic Orthopedists and is available at: https://ianmmedicine.org. © 2017 Yochum and the Academy of Chiropractic Orthopedists.

Femoral acetabular hip impingement (FAI) syndrome can be a source of anterior hip or groin pain usually and patients between the age of 20 to 40 years old. The prevalence of this diagnosis is approximately 10 to 15%. Clinical examination reveals anterior hip or groin pain exacerbated with full flexion and internal rotation of the hip. This is considered a positive anterior impingement sign (painful internal rotation is 90° of flexion). Pain can also be exacerbated in the sitting position or with sporting activity.

There are two types of bony deformity that can cause FAI. The first is the pincer deformity. This is also called acetabular over coverage as the contacting surface area of the femoral head on the acetabulum is larger. This can be seen on an AP radiograph with a crossover sign or an increased center edge angle (Figure 1 and 2). The normal measurement for the center edge angle should be less than 40°.

pincer cea

Figure 1 and 2: Pincer deformity with a center edge angle measuring approximately 52°.

The second type of osseous deformity is the CAM deformity. This is also called the pistol grip deformity due to the appearance of the femoral head neck junction similar to that of the handle of the pistol. The appearance of this CAM deformity is that of asphericity at the femoral head neck junction and has the appearance of an osseous bump. These are typically in the anterior lateral area of the femoral head neck junction. This is thought because by a variant of the epiphysis. Patients can also have a combination of both the pincer type and CAM type deformity.

Figure 3 and 4: CAM deformity seen at the anterior lateral femoral head neck junction on both the AP and frog leg projection (arrows).

Diagnosis is primarily clinical with the radiographic signs being supportive in nature.

Secondary radiographic signs of FAI include osteoarthritis, labral tears and labral ossification due to the abnormal stress placed on the hip joint with activity. A herniation pit, commonly seen within the femoral neck has been associated with FAI therefore clinical correlation for impingement should be performed when present. If there is concern for labral tearing an MRI arthrogram of the affected hip should be done with axial oblique images to evaluate and measure the CAM deformity.


Femoroacetabular Impingement: Radiographic Diagnosis- What the Radiologist Should Know. American Journal of Roentgenology. 2007;188: 1540-1552. 10.2214/AJR.06.0921

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