[Dynamic magnetic resonance of the knee. Considerations on techniques and anatomy with a magnetic resonance system with open magnet].

MRI is currently considered the best technique to study the joints--knee joints in particular. Most studies are performed with the knee straightened out or slightly flexed, which position is mandatory with contemporary MR units. Recently, however, the MR equipment for limb studies and the larger tunnels of total body magnets have permitted partially dynamic knee studies, up to 30-40 degrees flexion; this joint excursion cannot be exceeded. In 1996, Muhle and Niitsu demonstrated that dynamic MRI can be useful to study cruciate ligament injuries, some types of meniscal injuries, all femoropatellar conditions and, mostly, cruciate ligament reconstruction. We used an open magnet MR unit for thorough functional dynamic knee studies, acquiring the images at 0-120 degrees flexion. The open magnet MR unit permits free joint movements. We examined 25 subjects: 10 healthy volunteers and 15 patients with meniscal, capsuloligamentous, femoropatellar or synovial conditions. This technique schedules axial, coronal or sagittal images, according to the diagnostic suspicion, suitably directed with the patient in lateral decubitus and with the knee flexed to maximum joint excursion. Dynamic MR findings are easily transferred to an X-ray film, so that the radiologist can send them to the orthopedist with no need of any videotape or TV take. The current cine MR programs display the dynamic images of the moving joint on an MR monitor, but this option is not yet widely available. The quality of dynamic MR studies is exactly the same as that of conventional images, with a particular emphasis on the small diagnostic details of the injuries. We report our preliminary experience with this technique, indicating some possible clinical applications of dynamic MRI which permits thorough studies of knee flexion-extension.