MRI of the knee joint

Procedure

If a doctor at the hospital or in the practice orders an MRI of the knee, an appointment must first be made. Depending on the order situation and the reason for performing the knee MRI, the affected person may have to wait a few weeks for their appointment. Before the examination is actually performed, an informative discussion takes place, during which the physician informs the patient about the risks of the examination and, above all, about previous illnesses and operations.

The actual examination usually takes only about 15 to 30 minutes and is absolutely painless. It is important to lie still for the entire duration of the examination so that the images can be used. During the entire procedure, the examining physicians have a view into the MRI room and can talk to and understand the examined patients via intercom.

The MRI machine itself is very loud during the examination, which is why headphones or earplugs are usually provided to block out the loud noises. After the images have been taken, they have to be evaluated by a radiologist. In most cases, the treating physician discusses the individual findings with the examined person on site today.

However, this is a voluntary service and does not necessarily have to take place. The patient does not have to be sober for the MRI examination of the knee. The normal intake of food and beverages is possible.

In contrast, the patient must appear fasting during an MRI examination of the upper/lower abdomen (upper abdomen MRI, hydro MRI). An MRI of the knee can be performed on a fully clothed patient. Only the removal or deposit of all metallic objects (also on clothing) is urgently required.

There is a risk that these objects may heat up during the examination or that they may disturb or distort the MRI images. An MRI examination of both knees at the same time is possible in principle, but is not usually performed. There are several reasons for this.

On the one hand, the radiologist can only bill the health insurance companies for the MRI examination of one knee on the day according to the scale of fees for doctors. On the other hand, an examination of both knees takes a very long time overall (at least 40min), as the knees have to be examined separately one after the other. Since the patient should not move during this period and should maintain the position in which he or she is lying, the physician must decide before the examination whether an examination is possible.

Possible criteria for the doctor can be the patient’s age, physical condition and other diseases. Depending on the design, a distinction is made between closed and open MRI devices. Normally, in an MRI examination of the knee, the patient is pushed into the tube feet first, only up to the upper body.

This means that the head is usually outside the tube, so that people who suffer from claustrophobia can also be placed in a closed MRI tube (with the knee joints). Often, transmitter and receiver devices outside the MRI tube are used to transmit the radio waves and detect the impulses. In some cases – depending on where the corresponding knee coil is attached in the MRI series ́s – the patient must nevertheless enter the tube with his head.

This should always be clarified in advance, because if claustrophobia exists, alternatives must be sought. The latest MRI tubes have also been built so that they have a larger diameter and therefore no longer have such a restrictive effect. If necessary, a sedative can be administered by the radiologist.

In addition, the patient is always given a push button in his or her hand, which he or she can press during the examination in case of severe discomfort and thus abort the examination. In any case, it is important that the structure to be examined is not moved during the creation of the images, as the images created would then be unusable. Images blur, comparable to a photograph.

Depending on the indication, a contrast medium is injected into the vein during the MRI examination of the knee via an access. In general, the MRI allows a good contrast between the different soft tissue structures in the knee to be displayed and thus to distinguish them well from each other. The administration of contrast medium helps to identify very fine structures (e.g. smallest tears in the meniscus area) or to better visualize areas with blood circulation. Stable gadolinium chelates (good tolerability) are usually injected intravenously through an arm vein. These accumulate in the area of the knee, especially in areas with a high blood supply, and color them light or white.In comparison to the areas not supplied with blood (including cartilage tissue), which turn black, a strong contrast can be achieved.