We carried out radial MRI in 30 hips with moderate osteoarthritis and in ten normal hips. On a scout view containing the entire acetabular rim, 12 vertical radial slices were set at 15° intervals. Different appearances were observed in different parts of the joint. In the weight-bearing portion, from 45°a nterosuperior to 45° posterosuperior, 'attenuation' (n = 16) and 'disappearance' (n = 25) were observed as abnormalities of the labrum with 'capsular stripping' (n = 29) and 'extraosseous high signal lesion' (n = 27) as capsular abnormalities, seen more often in the anterosuperior portion. In all 12 planes there were osteophytes on the acetabular edge (n = 24), femoral head (n = 22) and/or at the central acetabulum (n = 6), a bone cyst on the acetabulum (n = 18) and/or the femoral head (n = 9), irregularity of the articular cartilage (n = 30), and an effusion (n = 28). Our findings indicate that radial MRI may be a useful non-invasive diagnostic method for demonstrating pathology in moderate osteoarthritis of the hip. Involvement of the labrum of the acetabulum in osteoarthritis (OA) of the hip, termed the acetabular rim syndrome in dysplastic hips 1 or an inverted acetabular labrum 2 as a cause of primary OA, has attracted some attention. Arthrography 3 and/or arthroscopy 4 have been used in the evaluation of abnormalities of the labrum, but these methods are invasive and provide limited images of the hip. MRI is non-invasive and can clearly depict morphological and qualitative changes in any direction. 5 We have previously reported a method using MRI to depict the entire acetabular rim by determining radial sections centred on the mid-point of the acetabulum. 6,7 With this technique we have now obtained radial MR scans of patients with moderate OA because of dysplasia, in whom conventional radiographs depicted 'marked narrowing of the joint space', and examined abnormalities of the acetabular rim including the labrum in the weight-bearing portion.
Patients and MethodsWe studied 24 patients (30 hips) with moderate OA whose conventional anteroposterior radiographs showed marked narrowing, but not obliteration, of the joint space. There were two men (two hips) aged 21 and 40 years and 22 women (28 hips) with a mean age of 45 years (29 to 57). The mean acetabular Sharp angle 8 was 47.7 ± 4.3° and the mean centre-edge angle of Wiberg 9 was 11.0 ± 12.2°.Ten other hips, eight in four healthy volunteers aged from 23 to 35 years and two in patients with unilateral nontraumatic osteonecrosis of the femoral head, were examined as a control group.For MRI we used a superconducting MR 1.5 Tesla imager (SMT-100X; Shimadzu, Kyoto, Japan) with an offcentre zoom technique and a local surface coil as a receiver antenna. The field of view was set at 20 cm and the matrix at 256 ϫ 256. T2-weighted radial images with a section thickness of 4 mm were obtained at 15° intervals using the STAGE method (TR, 500 ms; TE, 20 ms; flip angle, 30°) 10,11 in approximately four minutes. For this radial imaging, the scout view was determined as ...
