Pincer type femoroacetabular impingement
History from referring physician "degenerative changes in right hip?"
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Abnormal morphology of the acetabuli with over-coverage of both femoral heads. There is also bilateral coxa profunda as evident with the acetabular fossa (Figure B and C: dotted blue lines) medial to the ilioischial line (Figure B and C: yellow line). Overall imaging appearance is consistent with pincer type femoroacetabular impingement (AFI).
Two areas of impingement are present at the anterosuperior and inferomedial corners of the hip joints ( Figure B and C: asterisks and blue arrows) and more pronounced at inferomedial aspect of the hip joints.
Lateral projection of the right hip showed normal cutback at the femoral head-neck junction. (Figure C: dotted blue line and blue arrow).
This is a classic case of pincer type FAI. The demographics is also typical with 40 being the average age of presentation.
Pincer type FAI is characterised by one or more of the following abnormality including acetabular retroversion, coxa profunda and protrusio acetabuli. These changes leads to overcoverage of the femoral head by the overhanging acetabulum and resulting in impingement at the extreme of joint motion.
Typically pincer type FAI has a smaller anterosuperior coup lesion and a more pronounced contre-coup lesion posteriorly as demonstrated in this case. Pincer type FAI can co-exist with Cam type FAI thus assessment of the femoral head-neck junction is paramount to exclude co-existing pathology.