MRI appearance of popliteal cysts in childhood

Popliteal cysts are soft fluid-filled lesions of synovial origin which result from extrusion of joint fluid into the gastrocnemiosemimembranous bursa. They may occur in any age group, but 22-33 % occur in the first 15 years of life. In this age group they are rarely associated with intraarticular abnormalities and therefore rarely require treatment. This case report shows the magnetic resonance imaging (MRI) appearances of a popliteal cyst in two children.

Relationship between pulse sequences and signal intensity of joint fluid in the gradient-echo MR imaging

To depict the labrum and meniscus in terms of contrast to joint fluid by increasing its signal intensity, we examined in vitro and in a human subject the good imaging conditions of gradient-echo magnet resonance by using a 1.0 Tesla superconducting imager (Shimadzu). In our in vitro study, 3 types of joint fluid and physiological saline were imaged together with PVA gel (as the substitute for surrounding soft tissue), by using either the STAGE, SSFP, or STERF method, and with several TR's (repetition time); and mean signal intensity was obtained. In order to confirm the findings of the in vitro study, a human study was conducted: physiological saline was injected into a shoulder joint, and axial planes were depicted under the conditions equivalent to those of the in vitro study. With the STERF method, signal intensity of the fluid was high at any flip angle, but PVS gel and the surrounding soft tissues such as muscles were rarely depicted. With the STAGE and SSFP methods, depiction of the fluid, PVA gel, and the surrounding soft tissues were possible by setting an appropriate flip angle for TR: With the STAGE method (a spoiled gradient echo sequence), good imaging was possible by selecting small flip angle, regardless TR. Therefore, because of easiness in selecting conditions, the STAGE method is considered to be the best for diagnostic scanning.

High resolution MR imaging of the bilateral hips with dual phased-array coil

We applied dual-flex coils in a phased-array configuration to obtain high resolution MR images of the bilateral hips and compared the image quality with non-phased-array imaging. Multiple fast spin-echo images of both hips were obtained in a single acquisition. Two consecutive acquisitions with and without phased-array capability were performed in 22 hips and a fluid-filled phantom. The signal-to-noise ratio (S/N) enhancement values were calculated. Subjective image analysis was also obtained from three independent reviewers. High quality MR images were obtained using dual-array coils with a S/N enhancement value of 1.40 for a phantom and 1.83 to 2.22 for subject hips. On subjective analysis, the dual array enhanced delineation of the acetabular labrum, articular cartilage, and retained fluid. The dual array may be of diagnostic value with a higher S/N enhancement and subjective superiority of the images obtained.

MR findings in patients with acute tibial plateau fractures

OBJECTIVE

The purpose of this study was to demonstrate the MRI findings associated with acute tibial plateau fractures.

MATERIALS AND METHODS

MR scans of 29 patients with acute tibial plateau fractures were analyzed retrospectively. The images were evaluated for the presence of injuries involving the menisci, cruciate and collateral ligaments. The presence of a lipohemarthrosis or a simple joint effusion was also noted. The tibial plateau fractures were classified according to the scheme devised by Schatzker.

RESULTS

Evidence of internal derangement of the knee was found in 28 (97%) patients. Tibial collateral ligament (55%) injuries and lateral meniscus (45%) tears were noted most frequently. Medial meniscus tears were seen in 21% and fibular collateral ligament injuries were diagnosed in 34%. Forty-one percent had anterior cruciate ligament injuries while the posterior cruciate ligament was injured in 28%. Twelve (41%) patients demonstrated the characteristic MRI features of a lipohemarthrosis. Simple joint effusions were found in the remaining 17 (59%) patients.

CONCLUSION

MR imaging in patients with acute tibial plateau fractures commonly demonstrates associated ligamentous and meniscal injuries. By imaging in multiple planes, MRI can aid in the accurate characterization of tibial plateau fracture patterns and severity.

Systems view of optimizing metal on metal bearings

Metal on metal hip prostheses are critically reviewed as examples of a tribologic system. Because the inputs (load, velocity, fluid) are given, the designer has relatively few options, which can be exploited only if operative lubrication and wear mechanisms are known. Nothing can he done about the fluid, but film thickness can he influenced by macrogeometry (diameter and clearance) and by provision of film enhancing features. Microgeometry (surface topography, including asperity geometry and spacing) is a powerful contributor, but has not been sufficiently characterized or controlled. Compared with metal/polymer bearings, the total knowledge is small, and extensive research is called for. The high cost and long duration of hip joint simulation tests makes them more suitable to evaluate devices and to validate findings from bench tests. A particularly important task is to establish which experimental fluid adequately simulates the fluid formed around an all metal prosthesis. Much basic work can he conducted in bench tests, particularly in a form of oscillating twist compression test with cyclic loading, which induces squeeze film and mixed film lubrication. There is need for friction and wear studies with different metals and coatings, with controlled surface topography, and with lubricants specially formulated to clarify the roles played by various constituents of the fluid formed in metal on metal joints.

The rheumatoid knee before and after arthrocentesis and prednisolone injection: evaluation by Gd-enhanced MRI

In patients with rheumatoid arthritis, intraarticular injection of corticosteroids is an accepted means of treating a symptomatic joint. It has previously been impossible to precisely quantitate the effects of these injections on synovial effusion and pannus. Magnetic resonance imaging (MRI) is a safe, effective means of evaluating joint anatomy, and the use of intravenous gadolinium (Gd)-containing contrast allows clear differentiation of fluid from abnormal synovial tissue. The current study utilized MRI and Gd-labeled diethylene-triamene pentacetic acid (Gd-DTPA) contrast to evaluate serial changes in 6 knees of 6 patients with rheumatoid arthritis, following arthrocentesis and intraarticular injection of prednisolone. One week after the corticosteroid was injected, 2 patients had reduction of pannus width to 20% and 68% of baseline measurements. In these same individuals, follow-up sagittal views showed decreases of total effusion and fluid-plus-pannus width. The other 4 patients, who were followed for 4 weeks, had minimal changes in fluid and synovium. Gd-DTPA-enhanced MRI permits precise assessment of effects of intraarticular injections on synovial fluid and pannus in the rheumatoid knee.