Review Question - QID 214010

Figure A demonstrates a cross-over sign, which is indicative of acetabular retroversion.

Femoroacetabular impingement (FAI) results from abnormal contact between the femur and acetabulum which ultimately results in labral damage and various degrees of chondral damage. Two types of FAI are described: cam and pincer types. Cam impingement is a femoral based disorder in which the anterolateral femoral neck is too broad. Classic findings consist of a decreased head-neck ratio, aspherical femoral head, decreased femoral offset and femoral neck retroversion. Conversely, pincer type impingement is acetabular based and results from anterosuperior acetabular over coverage, acetabular retroversion and coxa profunda. Radiographically, patients with pincer lesions often have a cross-over sign in which the posterior wall “crosses over” the anterior wall which is indicative of acetabular retroversion.

Bedi et al review femoroacetabular impingement (FAI). They report that a cross over sign or ischial spine sign on a well aligned hip radiograph demonstrates acetabular retroversion anterosuperiorly and more normal anteversion inferomedially. They conclude that this deformity is associated with repetitive abutment of the femoral head-neck junction on the anterior acetabular rim in flexion/rotation and results in tearing of the labrum anterosuperiorly and associated cartilage damage.

Bryd et al review the cause and assessment of FAI in athletes. They report that this cause of intra-articular hip pathology affects athletes as they push their bodies beyond the diminished physiologic limits imposed by the altered joint morphology. They conclude that early recognition is the most important aspect of treatment in order to avoid severe secondary damage.

Figure A is the AP radiograph of the right hip demonstrating a cross-over sign indicative of acetabular retroversion. Illustration A is this same radiograph with the anterior wall outlined in teal and the posterior wall in black.

Incorrect Answers:
Answer 1: A shallow acetabulum with a lack of anterolateral coverage is indicative of dysplasia.
Answer 2: An aspherical femoral head is the pathologic processes in cam type impingement.
Answer 4: This patient has no radiographic signs of a stress fracture.
Answer 5: A pistol grip deformity, which is seen in cam-type lesions, may result from previous SCFE.