that MR imaging with intra-articular injection of gado- linium chelate (MR .... On MR arthrography, reliable indicators of labral trau- matic or degenerative ...
Eur. Radiol. 10, 83±88 (2000) Ó Springer-Verlag 2000
European Radiology
Pictorial review MR arthrography of the hip: normal intra-articular structures and common disorders L. Ghebontni, B. Roger, J. El-khoury, J. L. Brasseur, P. A. Grenier Department of Radiology, PitiØ-Salptrire Hospital, 83 boulevard de l'Hôpital, F-75013 Paris, France Received: 6 June 1998; Revision received: 2 January 1999; Accepted: 2 April 1999
Abstract. This pictorial review illustrates the anatomical features of normal intra-articular components of the hip and their common disorders on MR arthrography. On T1-weighted MR arthrograms, the normal contrast-filled joint cavity shows a homogeneous high signal intensity. Normal acetabular labrum appears as a well-delineated triangle showing a low signal intensity, surrounded by contrast material in the perilabral recess. Intra-articular paramagnetic contrast outlines labral tears, loose bodies, communicating labral cysts and cartilage lesions (traumatic tears, focal defects, degenerative fissures and thinning), and improves their detection. Overall, MR arthrography enables accurate detection and staging of hip intra-articular structure abnormalities. Key words: Hip ± MRI ± MR arthrography ± Acetabular labrum
Introduction Intra-articular pathology (labral abnormalities, cartilage lesions and loose bodies) is the main cause of hip pain [1, 2]. Early recognition and treatment can result in substantial pain relief [1]. Evaluation of the intra-articular components (acetabular labrum, articular cartilage and joint cavity) is based on CT arthrography and CT arthroscopy. The CT arthrography technique has not been consistently reliable in depicting labral lesions [3, 4]. Hip arthroscopy is not available at all institutions and is an invasive procedure with potential morbidity [4]. Several recent clinical studies [3, 4, 5, 6, 7] indicate that MR imaging with intra-articular injection of gadolinium chelate (MR arthrography) enhances the conspicuity of intra-articular structures of the hip [5] and enables accurate detection and staging of their abnormalities [3, 4]. This article defines the normal intra-articular structures of the hip as seen on MR arthrography and describes common disorders encountered in the hip. Correspondence to: L. Ghebontni
The MR arthrograms are correlated to conventional and CT arthrograms. All normal and pathological features illustrated herein were confirmed at arthroscopy. MR and CT arthrographic techniques Approval for intra-articular administration of gadolinium was obtained from the hospital's investigational review board and informed consent was obtained from all patients. Conventional, CT and MR arthrograms were obtained with intra-articular injection, under fluoroscopic control, of gadolinium tetra-azacyclododecane tetra-acetic (Gd-DOTA; Dotarem, Guerbet, Aulnaysous-bois, France) diluted in iodinated contrast material (Hexabrix 320, Guerbet, Aulnay-sous-bois, France). The dilution of Gd-DOTA was 1:300. The injected quantity of contrast solution was 8±10 ml. The MR and CT imaging was initiated within 30 min after the injection of contrast material. T1-weighted spin-echo (SE) images in the axial, sagittal and coronal planes were obtained on a 1.5-T unit (Signa, General Electric, Milwaukee, Wis.) using a surface coil and the parameters TR/TE = 580/17 ms, 4-mm slice thickness with a 1-mm interstice gap, a 17-cm field of view and a 256 256 matrix. Supplementary 3-mm slice thickness fat-suppressed T1-weighted SE images were obtained in several patients. The hip was placed in slight internal rotation. Computed tomography scans were performed on fourth-generation scanners using 1- to 2-mm axial sections, a 10- to 15-cm field of view and a 512 512 matrix. Reconstructions were obtained in sagittal and coronal planes. The hip was placed in slight internal rotation. Magnetic resonance and CT arthrographic findings were correlated with arthroscopic results. Normal hip On MR arthrograms, the contrast-filled joint cavity shows a homogeneous high signal intensity, outlined by the low signal of cortical bone, joint capsule and sur-
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d Fig. 1a±e. Normal hip: Right hip in a 21-year-old woman. a Anteroposterior conventional arthrogram. Superior labrum (arrowhead) appears as a triangle surrounded by contrast material within the perilabral recess (arrow). b Coronal T1-weighted spin-echo (SE) MR arthrogram. Normal acetabular labrum (arrowhead) appears as a well-delineated triangle showing a very low and homogeneous signal intensity, surrounded by contrast material within the perilabral recess (1). Joint capsule (arrow) inserts over the labrum. c Sagittal T1-weighted SE MR arthrogram. The joint capsule (arrow) inserts close above the labrum (arrowhead). The perilabral recess (1) is well delineated. d Axial T1-weighted SE MR arthrogram. Anterior (white arrow) and posterior (arrowhead) portions of the labrum are clearly visualized. The joint capsule (black arrow), delineated by contrast material (1), shows low signal intensity. e Axial CT arthrogram at same level as d. Anterior (arrow) and posterior (arrowhead) portions of the labrum are clearly visualized. The joint capsule is not differentiated form the surrounding soft tissues
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e rounding ligaments (Fig. 1) [3, 6]. In cases where the joint communicates with the iliopsoas bursa, the latter fills with contrast material and the communication is easily visualized on axial MR arthrograms (Fig. 2) [4, 6]. Unlike conventional MR imaging where the labrum is difficult to differentiate from the joint capsule (Fig. 3), intra-articular contrast material distends the joint and separates the labrum from surrounding tissues, leading to an improvement in the conspicuity of the labral shape, size and surface. On MR arthrograms (Figs. 1, 2), normal acetabular labrum appears as a well-delineated triangle showing a low and homogeneous signal intensity, surrounded by contrast material in the perilabral recess [3, 4, 5, 6, 7]. The labral base is attached to the margin of the acetabulum without a notch or a sulcus [3, 4, 6]. The joint capsule inserts over (Fig. 1 b) or close above (Figs. 1 c, 4, 6 a) the labrum on the acetabular rim [4, 6]. Superior and inferior labral portions are well visualized on coronal images (Fig. 1 b), whereas anterior and posterior portions are better displayed on axial (Fig. 1 d) and sagittal (Fig. 1 c) sections [6]. The inferior portion blends with the transverse ligament of the hip
L. Ghebontni et al.: MR arthrography of the hip
85 Fig. 2 a, b. Normal iliopsoas bursa in 41-year-old man. a Sagittal T1-weighted SE MR arthrogram. Contrast material within the iliopsoas bursa (1) indicates its communication with the joint. b Axial T1-weighted SE MR arthrogram. The communication (arrow) between the joint and the iliopsoas bursa (1) is easily visualized Fig. 3. Normal hip on conventional MR imaging in 32-year-old woman. Coronal T1-weighted SE image. Labrum cannot be differentiated from the surrounding joint capsule because they (1) show the same low signal intensity
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Fig. 4. Labral degenerative changes in 47year-old man. Coronal T1-weighted SE MR arthrogram shows an enlarged and increased signal intensity labrum (arrowhead). Note that the joint capsule (arrow) inserts close above the labrum on the acetabular rim
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Fig. 5. Labral tear in 32-year-old woman. Sagittal T1-weighted SE MR arthrogram shows a contrast-filled vertical tear (arrow) of the anterosuperior labrum
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L. Ghebontni et al.: MR arthrography of the hip Fig. 6 a, b. Absence of the superior portion of the labrum in 52year-old woman. a Coronal T1weighted SE MR arthrogram. Absence of the superior portion of the labrum (arrow). Joint capsule (arrowhead) inserts on the acetabular rim. b Conventional arthrogram shows findings similar to those found on MR arthrogram (a) Fig. 7a±d. Labral cyst in a 34year-old man. a Conventional arthrogram shows a labral cyst (arrow) communicating with the joint cavity through a labral tear (arrowhead). b Coronal and c T1-weighted SE MR arthrograms. The labral cyst (arrow) communicates with the joint cavity and fills with contrast material. d Pathologic specimen showing the cyst (arrow) of the labrum (arrowhead)
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[4]. The size of the labrum is variable, the length (distance from base to tip) ranging from 4 to 12 mm. Acetabular and femoral head cartilages show an intermediate signal intensity well delineated by the very low signal of the subchondral bone (Fig. 1) [6, 7]. Labral pathology
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On MR arthrography, reliable indicators of labral traumatic or degenerative conditions include morphological alterations and changes in signal intensity within the labral substance [5]. Labral enlargement, irregular margins and areas of increased signal intensity on T1-weighted images indicate degenerative changes (Fig. 4) [4, 5, 6]. Traumatic lesions lead to tears that occur almost exclusively in the anterosuperior labrum [4, 6, 7, 8]. The
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Fig. 8a±c. Femoral head cartilage tear in a 19-year-old professional tennis player. a Axial fat-suppressed T1-weighted SE MR arthrogram. Contrast material fills a femoral head subchondral cyst (1) communicating with the joint cavity through a cartilage tear. b Sagittal fat-suppressed T1-weighted SE MR arthrogram shows the labral tear (arrow) and the subchondral cyst (1). c A CT arthrographic sagittal reconstruction at same level as b. Femoral head subchondral cyst (arrowhead) communicating with the joint cavity through a cartilage tear (arrow) Fig. 9 a, b. Degenerative cartilage disorders in a 35-year-old male ballet dancer. a Coronal and b sagittal T1-weighted SE MR arthrograms show contrast-filled acetabular subchondral cysts (arrow) communicating with the joint space through associated defects of the acetabular cartilage (arrowhead)
majority of these tears are found at the labral base, leading to its separation from the acetabular rim, with or without labral displacement [3, 4, 8]. Magnetic resonance arthrograms show contrast material running in the acetabular±labral interface [3, 4]. In some cases the avulsed labrum may abut and erode the femoral head cartilage [8]. Partial or complete tears can also occur through the labral substance and are showed on MR ar-
9b thrograms as high-signal-intensity contrast-filled fissures (Fig. 5) [4, 6]. Complete transversal tears detach the distal portion of labrum and give a labral blunting or a Parrot-beak aspect [4, 8]. Cleavage tears within the substance of the labrum can also occur [8]. The value of absence of a portion of the labrum (Fig. 6) in a symptomatic patient is controversial [4]. The aetiology of labral cysts is not well elucidated. They can be related to aging [9] or can be associated with labral tears [4, 6]. Some cysts communicate with the joint cavity through the associated tear and fill with contrast material on MR arthrography (Fig. 7) and CT arthrography [6], whereas non-communicating cysts located within the labral substance are visible only with MR imaging. Cartilage disorders The MR arthrography technique can be helpful in patients (especially athletes overusing their hip joint) presenting with mechanical hip pain and normal findings on conventional imaging, in order to search for cartilage traumatic injury or mild degenerative lesions.
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c Magnetic resonance arthrograms show contrast-filled cartilage traumatic tears (Fig. 8) and degenerative fissures (Fig. 9), sometimes communicating with subchondral cysts (Figs. 8, 9) [6]. Localized cartilage defects (Fig. 9) or focal acetabular and femoral head cartilage thinning can also be seen [6, 7]. Idiopathic synovial osteochondromatosis Intra-articular loose bodies cannot be differentiated from surrounding tissues on conventional MR imaging which is deceptive in their detection. The CT arthrography technique is not consistently reliable in the detection of osseous loose bodies. On MR arthrography (Fig. 10) loose bodies are surrounded by contrast material, which improves their detection and enables an accurate determination of their number and topography [6, 7]. Thus, MR arthrography is helpful in depicting loose bodies in the acetabular fossa which removal can require surgical hip dislocation. Associated osteochondral lesions (Fig. 10) may be encountered, indicating secondary osteoarthritis. Conclusion The MR arthrography technique enables accurate assessment of intra-articular pathology [3, 4, 5, 6, 7]. It permits direct visualization of all intra-articular structures,
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Fig. 10a±c. Idiopathic synovial osteochondromatosis in 39-yearold man. a Arthrography shows many intra-articular cartilaginous bodies (1). Femoral and acetabular cartilage thinning (arrow) indicates secondary osteoarthritis. b Axial T1-weighted SE MR arthrogram. Intra-articular cartilaginous bodies (1), surrounded by contrast material, show intermediate signal intensity. Acetabular subchondral cysts (arrow) communicating with the joint through cartilage lesions. c Axial CT arthrogram at same level as b shows findings similar to those found on axial MR arthrogram (b)
and allows, by virtue of its excellent soft tissue contrast, a complete evaluation of the joint. Additionally, intraarticular paramagnetic contrast material distends the joint, separates the labrum from the capsule, and defines labral and cartilage tears. The axial, sagittal and coronal MR sections are essential for complete visualization of the entire intra-articular components, particularly the labral anterosuperior portion, where most tears are located. Small slice thickness of 4 mm or less is indispensable for accurate evaluation of hip joint. References 1. Altenberg AR (1977) Acetabular labrum tears: a cause of hip pain and degenerative arthritis. South Med J 70: 174±175 2. McCarthy JC, Busconi B (1995) The role of hip arthroscopy in the diagnosis and treatment of hip disease. Orthopedics 18: 753±756 3. Czerny C, Hofmann S, Neuhold A et al. (1996) Lesions of the acetabular labrum: accuracy of MR imaging and arthrography in detection and staging. Radiology 200: 225±230 4. Petersilge CA, Haque MA, Petersilge WJ, Lewin JS, Lieberman JM, Buly R (1996) Acetabular labral tears: evaluation with MR arthrography. Radiology 200: 231±235 5. Hodler J, Yu JS, Goodwin D, Haghighi P, Trudell D, Resnick D (1995) MR arthrography of the hip: improved imaging of the acetabular labrum with histologic correlation. AJR 165: 887±891 6. Ghebontni L, Roger B, Brasseur JL, Grenier PA (1996) Intraarticular pathology of the hip: MR arthrographic findings (abstr). Radiology 201: 532 7. Marianacci EB, Palmer WC, McCarthy JC (1995) MR arthrography of the hip: preliminary results with surgical correlation (abstr). Radiology 197: 395 8. Fitzgerald RH Jr (1995) Acetabular labrum tears. Diagnosis and treatment. Clin Orthop 311: 60±68 9. Ueo T, Hamabuchi M (1984) Hip pain caused by cystic deformation of the labrum acetabulare. Arthritis Rheum 27: 947±950
