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.

The intra-epiphyseal growth of the proximal femur has been focus of studies because of the potential relationship with the development of slipped capital femoral epiphysis and cam deformity in femoroacetabular impingement. We aimed to evaluate the developmental pattern of the epiphyseal tubercle and extension in normal boys and girls from eight to fifteen years, without hip conditions. We performed three-dimensional (3D) analysis of pelvic computed tomographic scans of 80 subjects with suspect of appendicitis, consisting of five boys and five girls for each age, from eight to 15 years old. Images were segmented slice by slice at the level of the growth plate using biplanar orientation. The 3D-segmented epiphyses were used to measure the location and height of the tubercle, the height of the epiphyseal extension, and the epiphyseal diameter. We found that the epiphyseal tubercle was eccentrically located at the posterolateral quadrant of the physeal surface. The absolute height of the epiphyseal tubercle did not vary between ages (R. 2. =0.04; p=0.101). The epiphyseal diameter increased with age (R. 2. =0.74; p<0.001), making the tubercle height proportionally smaller with the epiphyseal growth (9% reduction in tubercle height normalised by the epiphyseal diameter). The normalised epiphyseal extension height significantly increased by 160% from 8 to 15 years of age. Our observation validates the hypothesis of the cupping mechanism provided by the peripheral growth of the epiphyseal extension, while the epiphyseal tubercle relatively decreases in size during the skeletal growth. Further research will be important to determine the role of these structures in the epiphyseal stability

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: Bone Joint J 2013;95-B:893–9.

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.