Some forms of femoroacetabular impingement pincer type (see section "What is femoroacetabular impingement?") result from poor spatial position of the acetabulum and not just from excess of anterior or posterior wall. In this situation the size of the cavity can be normal, but its position is deeply altered and instead of the opening being anterior (video 1) is posterior (video 2). The lines which mark its anterior and posterior limit (walls) intersect and the line that marks its posterior limit is located medial to the geometric center of the joint (posterior wall sign).

To address this situation is not enough remove excess of anterior coverage (anterior acetabular wall), it is necessary to re-orient the entire cavity with an inverted periacetabular osteotomy (see section ""Bernese" Periacetabular Osteotomy").

Radiograph of a pelvis with acetabular retroversion

Radiograph of a pelvis with significant acetabular retroversion. Note the intersection of lines nearly at half of its height (acetabular retroversion index of about 50%)

Radiography of the acetabulum

Radiography of a real pelvis with the edges of the acetabulum marked with a metallic wire. On the radiography we view a normal expression of the acetabulum walls.

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