Risks of a MRI ́s from the knee
In general, the performance of an MRI is very safe and usually has no side effects. There are risks due to the strong magnetic field if certain things are not observed. For this reason, it is important that a thorough explanatory talk is conducted by a doctor before the MRI is performed.
Any metal parts on the body are a particular problem. This also applies to things that have had to be surgically implanted, for example due to a fracture. Metal objects that can be removed must be removed before the MRI examination.
If there are metal parts in or on the body that cannot be removed, the MRI examination may not be possible and an alternative must be found. Especially if metal implants have been inserted in the knee during previous surgery ́s, e.g. after anterior cruciate ligament rupture, fracture of the tibial plateau, etc., an MRI of the knee can be performed in many cases. However, it must be noted that no information about tissue structures can be obtained directly from the implant, as the image is erased by the metal implant.
Often implanted pacemakers, bone nails or plates, and insulin pumps are reasons not to perform the examination. In some MRI examinations, so-called contrast agents are also used, which in rare cases can lead to allergic reactions. Even in the case of existing kidney diseases, the treating physicians should be informed before an MRI with contrast medium is performed.
Indication
In order to better assess certain diseases or to facilitate the diagnosis of unclear knee pain, MRI examinations of the knee are often performed. Here, the findings of the MRI can also show which therapy is suitable for the individual disease and whether, for example, there is an indication for surgery. Although bony structures can be assessed less well in MRI compared to CT, fractures, tumors or other defects of the bone can also be detected in MRI.
MRI examinations are particularly frequently ordered when there is a suspicion that cartilage structures are damaged (cartilage damage). For example, a damaged meniscus or torn cruciate ligament can be easily diagnosed with an MRI. MRI of the knee is also frequently used in cases of fluids or abscesses in and around the joint.
Finally, MRI can also be used to detect damage to the ligament and muscle apparatus of the knee joint. Probably the most common indication for an MRI is a torn meniscus. (see below)The meniscus, which acts as a shock absorber between the thigh and lower leg, is subject to natural wear and tear over the course of its life and can tear.
A torn meniscus caused by an accident is much less common. An MRI of the knee joint can show a torn meniscus relatively reliably. But especially the transition of a severe degeneration into a degenerative meniscus tear is sometimes difficult to distinguish radiologically.
In order to assess the condition of the cartilage or the cartilage damage in the knee from the outside, the MRI is the best diagnostic option. Since cartilage has a high water content, it is clearly distinguishable from the bone on which it rests. Higher degrees of cartilage damage (CM 3° and 4°) can be reliably detected.
Minor cartilage damage and surface roughness are not always clearly visible on an MRI of the knee. In general, the assessability of cartilage damage in the knee is improved by MRI if the damage is worse. Cartilage damage behind the kneecap is particularly easy to assess, as this is where the cartilage in the knee is thickest and the cartilage damage can be visualized particularly well.
The cruciate ligament can be visualized very well in the MRI. The anterior and posterior cruciate ligament can be followed over its entire length on corresponding MRI images. In most cases, a complete tear of the anterior cruciate ligament can also be reliably diagnosed by an MRI of the knee.
The situation is considerably more difficult if the cruciate ligament is only torn. It remains difficult to assess by MRI how stable the remaining cruciate ligament is, even with the ever improving image quality. Especially if the mucous membrane tube, which is more elastic than the anterior cruciate ligament, does not travel with it, a torn cruciate ligament can lie in an intact tube.A Baker’s cyst is a sac in the posterior joint capsule in which joint fluid accumulates. An MRI examination is usually not required to detect the cyst (detection with sonography is possible), but to be able to distinguish possible causes of cyst formation. Baker’s cysts often occur in the context of degenerative meniscus lesions or in chronic polyarthritis.
