Table 2 Criteria for defining FAI types

Cam

1. Alpha angle is > 55°;

2. Anterior head-neck offset < 10 mm;

3. Anterior head-neck offset ratio < 0.15

*Must meet 2/3 criteria to be considered cam impingement

Pincer

1. Acetabular depth < 3 mm;

2. Lateral centre-edge angle > 39°;

3. Acetabular anteversion (in the upper third of the femoral head) < 0°

*Must meet 2/3 criteria to be considered pincer impingement

Mixed

*Must meet 2/3 criteria each for cam and pincer impingement (as per above) to be considered mixed impingement