[Imaging of external instabilities of the patella. State of the art]. / Imagerie des instabilités externes de la rotule. Mise au point.

External femoropatellar instability is a dynamic abnormality from various origins: osseous, cartilaginous or musculotendinous; X-rays films cannot give a precise enough description of this phenomenon. Attention is drawn by anterior pain or a sensation of instability. Clinical analysis distinguishes between permanent, traumatic or transient dislocations which are now more frequently discovered as part of a femoro-patellar syndrome with or without cartilage involvement. Conventional imaging, CT-scan and MR imaging are based on faultless techniques. Lateral views precisely report femoropatellar architectural abnormalities and patellar instability. Skyline views are able to quantify the various parts of the dysplasia. Dynamic tests increase the sensitivity of the plain films. But the main shortcoming of these techniques is the lack of visualization of the initial patellar engagement in the trochlea. The femoropatellar component of the knee arthrography visualizes rather large cartilaginous lesions. CT-scan, better than skyline views, allows examining the patellar bone without interference with the trochlea (extended knee), during the engagement (15 degrees flexed knee) and after the engagement (30 degrees flexed knee). However, the examination technique varies from one author to another according to his own pathophysiologic understanding. With the bicondylar plane reference, the reliability of the CT-scan measurements are better than skyline views. Like the dynamic tests during the beginning of the patellar engagement at 15 degrees, flexion is more sensitive than those at 30 degrees. Finally, CT-scan arthrography demonstrates thinner cartilaginous lesions than conventional arthrography. Presently the main contribution of MR imaging consists of detecting transient patellar dislocation that a single clinical examination cannot differentiate from other internal knee disorders. MR imaging is more precise in analyzing the cartilaginous structure. Kinematic MR imaging, still in an experimental stage, offers a new approach to the dynamic study of the patellar tracking.

Acute trauma of the extensor hood of the metacarpophalangeal joint: MR imaging evaluation.

PURPOSE: To assess detectability of the components of the extensor hood, especially the sagittal bands, with magnetic resonance (MR) imaging in normal and injured metacarpophalangeal (MP) joints. MATERIALS AND METHODS: T2*-weighted, T1-weighted, and contrast material-enhanced T1-weighted images were obtained of 54 normal MP joints (108 sagittal bands). The ability to detect the sagittal bands with each sequence was rated for three observers. These same sequences were used for MR imaging of nine patients with acute MP injury. Seven patients underwent surgery. RESULTS: The sensitivity of MR imaging for the detection of normal sagittal bands was 0.89-0.92 for T2*-weighted images, 0.80-0.88 for T1-weighted images, and 0.81-0.91 for contrast-enhanced T1-weighted images. MR imaging findings in patients with extensor hood injury included irregularity, poor definition, and increased signal intensity or uptake of contrast material by structures in and around the extensor hood. All MR imaging findings correlated well with those of surgery. CONCLUSION: MR imaging is accurate for determination of the presence and severity of injury to the extensor hood.

[Villonodular synovitis of the knee. Contributions of MRI]. / Synovite villo-nodulaire du genou. Apports de l'IRM.

This retrospective study included eight patients with villonodular synovitis of the knee (7 nodular forms and one villous form) who underwent magnetic resonance imaging and at least one arthroscopy. Joint enlargement and mild pain were the main manifestations. Other imaging studies provided little information. Magnetic resonance imaging showed highly suggestive hemosiderin-laden masses. Hemosiderin was most clearly seen on gradient echo sequences. Magnetic resonance imaging was also useful for determining the distribution of lesions. Intravenous gadolinium provided no additional information. Arthroscopy allowed to collect biopsy specimens and to perform synovectomy when called for. In our opinion, after a physical examination and plain roentgenograms, magnetic resonance imaging and arthroscopy should both be performed to determine the extent of lesions and to allow histological diagnosis and synovectomy, respectively.

Intraarticular diffusion of Gd-DOTA after intravenous injection in the knee: MR imaging evaluation.

Intraarticular concentration of gadolinium tetraazacyclododecanetetraacetic acid (DOTA) after intravenous injection and the diagnostic contribution of the subsequent arthrographic effect were assessed for meniscal lesions in the knee. Kinetics were studied in three healthy volunteers. Passage of contrast material into the synovial fluid of the joint was evaluated in 53 knees by measuring the signal intensity on T1-weighted images before, immediately after, and 1 hour after injection. Synovial fluid enhancement was 1.46-fold greater than the unenhanced value after 10 minutes, plateaued after 30 minutes, and was 1.95-fold greater after 1 hour. In articular fluid samples from four patients 1 hour after intravenous injection, the average intraarticular concentration was 141 mumol +/- 47 (1 standard deviation) at atomic absorption spectrophotometry. Knee mobilization improved the passage of contrast material into the synovial fluid by approximately 120% at 10 minutes and 25% at 1 hour. In eight of 39 tears, unenhanced standard sequences were equivocal. In seven of these uncertain cases, delayed contrast-enhanced images permitted adequate interpretation. Intraarticular concentration of Gd-DOTA produces a sufficient arthrographic effect for meniscus evaluation.

MR imaging in intracystic hemorrhage of simple hepatic cysts.

Intracystic hemorrhage of simple hepatic cysts is one of the most frequent complications. Ultrasonography (US) and computed tomography (CT) may show abnormal findings and mimic other diseases. We describe magnetic resonance (MR) imaging in four patients with intracystic hemorrhage confirmed by surgery or percutaneous aspiration. In all cases the lesions were hyperintense on both T1- and T2-weighted sequences. In three of the four cases the signal was heterogeneous on T1-weighted sequences. Two cases of a thickened wall and one case of a fluid-fluid level were also observed. We suggest that MR imaging may be helpful to differentiate intracystic hemorrhage from other cystic lesions by showing high signal on T1- and T2-weighted sequences.