Cam type femoroacetabular impingement (FAI) is due to an aspheric femoral head, which is best quantified by the alpha angle described on MRI and CT-scan. Radiographic measurement of the alpha angle is not well codified and studies from the literature cannot conclude on the best view to measure it. Most authors also describe a mixed type FAI which associates an aspheric femoral head with an excessive anterior acetabular coverage of the femoral head. Anterior center edge (ACE) angle has been described on the false profile view to measure anterior acetabular coverage in hip dysplasia and has never been evaluated in FAI. In this study, we developed a new lateral hip view which associates a lateral view of the femoral neck and a false profile view of the acétabulum, which we called profile view in impingement position (PVIP).

Twenty six patients operated for FAI had CT-scan, the PVIP and the false profile view of one or two hips according to pain. A control group of 19 patients who did not suffer from the hip had the PVIP. Alpha angles were measured twice on 17 CT scan of FAI patients by two observers and compared with the alpha angles measured on the corresponding hip PVIP by a correlation analysis. Alpha angles were measured twice on 45 PVIP in FAI patient and on 19 PVIP in the control group by three observers. ACE angles were measured once on 15 PVIP and on 15 false profile views. Means were compared by two tail paired t-tests, intra- and inter-observer reliability were measured by intraclass correlation coefficient.

Mean alpha angle on CT scan was 65.8° and 65.6° for observers 1 and 2 respectively (p>0.05). It was 63.6° and 64.3° on the PVIP (p>0.05). No significant difference was found between CT scan and radiographic measurements, and Pearson's correlation coefficients were good at 0.74 and 0.8. ICC was 0.86 for inter-rater reliability, and 0.91 for intra-rater reliability for CT-scan alpha angle measures. ICC for PVIP measures varied from 0.82 to 0.9 for intra-rater reliability and from 0.6 to 0.9 for inter-rater reliability. Mean alpha angle measured on PVIP in FAI patients was 63.3° and was 44.9° in control subjects and the difference was significant (p<0.001) for the three observers. None of the FAI patients and 88% of the control subjects had an alpha angle < 50°. Mean ACE angle was 26.8° on PVIP and 32.8° on the false profile view, the difference was significant (p=0.015), and the Pearson's correlation coefficient was moderate (r=0.58).

The PVIP is a reliable radiographic view to measure the alpha angle. It allows a good quantification of the alpha angle comparable to CT-scan measurements and permits to differentiate patients from control subjects. PVIP is not a good view to quantify anterior edge angle probably because of acetabular retroversion due to the hip flexion needed in this view. Mean ACE angle measured on the false profile view in FAI patient was comparable to ACE angle in general population reported in the literature.

Purpose of the study: Labrum lesions can be an important source of hip pain. Besides the classical causes, certain morophological anomalies can be associated with labrum lesions. The purpose of this work was to study the contribution of plain x-rays to the search for morphological anomalies of the hip in patients with labrum lesions.

Materials and methods: Twenty-six patients with labrum lesions were included in this study. The plain x-rays protocol included an anteroposterior view of the pelvis in the standing position, a Lequesne oblique view and a lateral view of the neck in the hip flexion position. Patients with severe hip dysplasia (VCA or VCI < 15° or THE > 15°) were excluded. Measurements were made after digitalization using a dedicated software. Measures were: neck-shaft angle, acetabular cover, lateral alpha (neck axis, center of the head, most lateral point of the head sphere), lateral offset, acetabular version. Femoral data in flexion were compared with 20 controls.

Results: Acetabular cover was considered moderately insufficient in five patients (VCA and/or VCE 15–25°). These patients had the same alpha angle as the control population (56°), i.e. no anomaly of the neck-head junction. The 21 patients with non-dysplastic hips exhibited a significantly greater alpha angle (64±9° versus 54.6±8°, p< 0.01) than the controls. All controls presented an alpha angle ≤ 69°. Among the 21 non-dysplastic patients, five presented coxa vara (< 125°), five acetabular retroversion, nine an alpha angle > 69°. In all, 77% of patients presented morphological anomalies of the hip. Among the six «normal» hips using these measures, three presented a pistol-grip aspect which could not be quantified with these measures.

Discussion: This analysis confirms the association between morphological anomalies detectable on plain x-rays and labrum lesions in patients who do no present severely insufficient acetabular coverage. We were unable to detect any difference in femoral offset compared with the control population.

Conclusion: A standard x-ray protocol can, in the majority of cases, detect morphological anomalies of the hip, an important etiological diagnostic element for understanding pathogenic mechanisms.