This study examined the relationship between the cross-over sign and the true three-dimensional anatomical version of the acetabulum. We also investigated whether in true retroversion there is excessive femoral head cover anteriorly. Radiographs of 64 hips in patients being investigated for symptoms of femoro-acetabular impingement were analysed and the presence of a cross-over sign was documented. CT scans of the same hips were analysed to determine anatomical version and femoral head cover in relation to the anterior pelvic plane after correcting for pelvic tilt. The sensitivity and specificity of the cross-over sign were 92% and 55%, respectively for identifying true acetabular retroversion. There was no significant difference in total cover between normal and retroverted cases. Anterior and posterior cover were, however, significantly different (p <
0.001 and 0.002). The cross-over sign was found to be sensitive but not specific. The results for femoral head cover suggest that retroversion is characterised by posterior deficiency but increased cover anteriorly.
Orthopaedic surgeons have accepted various radiological
signs to be representative of acetabular retroversion, which is
the main characteristic of focal over-coverage in patients with
femoroacetabular impingement (FAI). Using a validated method for
radiological analysis, we assessed the relevance of these signs
to predict intra-articular lesions in 93 patients undergoing surgery
for FAI. A logistic regression model to predict chondral damage
showed that an acetabular retroversion index (ARI) >
20%, a derivative
of the well-known cross-over sign, was an independent predictor
(p = 0.036). However, ARI was less significant than the Tönnis classification
(p = 0.019) and age (p = 0.031) in the same model. ARI was unable
to discriminate between grades of chondral lesions, while the type
of cam lesion (p = 0.004) and age (p = 0.047) were able to. Other
widely recognised signs of acetabular retroversion, such as the
ischial spine sign, the posterior wall sign or the cross-over sign
were irrelevant according to our analysis. Regardless of its secondary
predictive role, an ARI >
20% appears to be the most clinically
relevant radiological sign of acetabular retroversion in symptomatic
patients with FAI. Cite this article:
Using radiography and computer tomography (CT) we studied the morphology of 83 hips in 69 Caucasian adults with osteoarthritis secondary to developmental dysplasia of the hip (DDH). A previously published series of 310 hips with primary osteoarthritis was used as a control group. According to the Crowe classification, 33 of the dysplastic hips were graded as class I, 27 as class II and 23 as class III or class IV. The intramedullary femoral canal had reduced mediolateral and anteroposterior dimensions in all groups compared with the control group. Only in Crowe class II hips was the femoral neck-shaft angle increased. The proximal femur had more anteversion in all the developmental dysplasia of the hip groups, ranging from 2° to 80°. Templated measurement of acetabular dimensions for plain radiography closely matched measurements taken by CT. The results of our study confirm the observations previously confined to the Japanese population.
