Femoral acetabular impingiment
Constrictive pain to the proximal portion of the left thigh
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In this x-ray are recognizable three typical signs of femoral acetabular impingiment pincer type:
- The cross-over sign is reflected in the AP projection with an overhanging anterior acetabular margin. The anterior and posterior walls of the acetabulum projectionally intersect midway over the femoral head creating a figure 8 appearance.
- There is prominently seen ischial spines indicating acetabular retroversion. These are normally not visible on anterior-posterior radiographs.
This is a femoral acetabular conflict due to anterior acetabular wall overcoverage, which encounters the femoral neck early with end range of motion. The term "pincer” comes from the acetabulum pinching on the proximal femur.
The pincer effect may be due to a partial acetabular retroversion, acetabular overcoverage with or without coxa profunda, in which the head of the femur is fully covered by the acetabulum.
Impingement type clamp can be congenital, developmental or acquired. In the latter case can be the outcome of a periacetabular osteotomy or fracture.
Pincer-type FAI more often occurs in women.