Knee Magnetic Resonance

Generality

MRI is one of the most important medical tools for the detailed visualization of the various structural components of the knee (bone portions, articular cartilage, meniscus, ligaments, tendons, etc.).

Through its realization, radiologist and orthopedist are able to: establish the reason for knee problems, such as pain, swelling and / or stiffness; diagnose traumatic injuries such as knee sprains; identify lesions affecting the cartilage or menisci; highlight fractures in the femur, tibia or patella; diagnose osteomyelitis; etc.

Unless a contrast agent is used, preparation for magnetic resonance imaging is very simple, with few rules that must be followed.

With a duration not exceeding 30 minutes, magnetic resonance imaging of the knee is an examination that presents some contraindications; among these, the presence, within the human body, of devices or fragments of metallic nature deserves special mention.

The risks of magnetic resonance in the knee without using the contrast medium are minimal, close to zero.

Valuable results are available within 3-4 days.

A brief review of what MRI is

Magnetic resonance, whose full name would be nuclear magnetic resonance, is a diagnostic test that allows the visualization of the inside of the human body, without resorting to surgical incisions or ionizing radiations, but thanks to harmless magnetic fields and equally harmless radio waves .

Virtually free of side effects and with very few contraindications, magnetic resonance imaging provides clear and detailed three-dimensional images of so-called soft tissues (nerves, muscles, ligaments, fat, blood vessels etc.) and of the so-called hard tissues (bones and cartilages). This makes it a test of absolute relevance in many fields of medicine: from traumatology to oncology, passing through orthopedics, gastroenterology, cardiology, etc.

The only limit of magnetic resonance is the high cost of the equipment, necessary for the creation of magnetic fields for the observation of the human body, and the maintenance costs of the aforementioned equipment.

What is knee MRI?

Knee magnetic resonance imaging (MRI) is one of the most important diagnostic tools for visualizing, from different angles, every single component of the knee joint, namely: the distal end of the femur, the proximal end of the tibia, the patella, articular cartilage, meniscus, so-called knee ligaments, tendons, synovial membrane and synovial bursae.

MRI is a diagnostic test that can be performed in most hospitals and radiology clinics.

Like any other type of nuclear magnetic resonance, it is one of the practices of the Radiology medical specialty, so the reading of its results is the responsibility of a radiologist .

Indications

Knee magnetic resonance imaging has mainly diagnostic utility. In fact, it allows:

Go back to the origin of symptoms (which clearly have the knee as object), such as pain, joint stiffness, swelling, a sense of weakness and the presence of one or more hematomas;
Identify the damage and injury to the articular cartilage, the lateral meniscus and / or the medial meniscus;
Diagnose the so-called knee sprains, ie traumatic knee injuries that are characterized by stretching or injury of ligaments and / or tendons. Knee sprains are very common among those who play sports; it is no coincidence that knee magnetic resonance imaging is a diagnostic practice widely practiced in sports;
Also trace the slightest bone fracture on the distal end of the femur or the proximal end of the tibia;
Diagnose the degenerative processes, of an inflammatory nature, against the joint. In medicine, joint inflammation takes the generic name of arthritis . A very common form of knee arthritis is osteoarthritis; osteoarthritis of the knee is also known as gonarthrosis ;
Identify and clarify the causes of the so-called knee spill (or water in the knee);
Diagnosing osteomyelitis, an infectious process affecting the bones, which generally affects the knees, shoulders and, in general, the bones rich in cancellous tissue;
Highlight the patella injuries and bring to light the causes.

Furthermore, knee magnetic resonance is useful for orthopedic doctors to determine whether or not it is necessary to resort to arthroscopy of the knee or another type of surgery (always, of course, on the knee), and to monitor the progress of a subjected knee at surgery.

A particular type of magnetic resonance in the knee: magnetic resonance with contrast

There is the possibility of increasing the sensitivity and specificity of a magnetic resonance imaging knee, through the use of a contrast medium, injected into the patient intravenously.

Magnetic resonance imaging using a contrast medium is an example of magnetic resonance with contrast of a joint or arthrogram .

Magnetic resonance with contrast of a joint or, more generally, of any other part of the body provides three-dimensional images that are more detailed and full of details compared to a conventional magnetic resonance, that is, without a contrast agent.

Preparation

The preparation for magnetic resonance in the knee is the same as in the case of all other types of magnetic resonance without contrast medium.

This means that:

No fasting or observance of special diets is foreseen, unless otherwise indicated by the radiologist;
Shortly before the examination, the patient must take off any garment or object containing metal parts (bags, wallets, shoes, jewelry, etc.), answer a specific questionnaire that checks whether or not there are contraindications to the examination and, finally, communicate if you suffer from claustrophobia and, in the case of a female patient, if you are pregnant (or suspected).

Preparation in the event of magnetic resonance with the knee

If the knee magnetic resonance involves the use of the contrast medium, the preparation for the exam undergoes some variations, compared to what was stated previously.

In fact, differently from what happens during a conventional magnetic resonance to the knee, the patient must:

Complete the questionnaire that checks for any contraindications before the exam and with the signature of your primary care physician, and take it with you on the day of the procedure;
Perform a blood creatinine test ( creatininemia ) near the MRI with contrast (not before 30 days) and take the results with you on the day of the exam, to show them to the radiologist together with the questionnaire concerning the contraindications;
Observe a complete fast in the last 6 hours before the exam.

Figure: knee magnetic resonance using a classic device. As can be seen from the photograph, before the introduction of the patient into the cylindrical machinery, he foresees the encapsulation of the knee in a special structure for the creation of images, through the magnetic fields and the radio waves of the main apparatus.

Figure: knee magnetic resonance using a device for the extremities of the body only. As can be seen from the photograph, the patient inserts only the affected limb into the diagnostic machinery; the rest of the body remains completely outside.

Procedure

The knee magnetic resonance machine can be the classic cylindrical device, capable of accommodating the patient inside, once lying on a special sliding bed; or it can be a device of decidedly smaller dimensions, designed to accommodate only the extremities of the body (legs, feet, arms, etc.), so as to avoid the confinement of the patient in a narrow space and in a certain sense "more oppressive".

The images on the side show the two possible machines with which it is possible to realize a magnetic resonance to the knee.

Coming to the actual procedure, this starts with the request to the patient, by a radiologist technician, to deprive himself of every forbidden object and garment and with the answer to the questionnaire concerning the contraindications.

Once this very first part has been completed, the patient must sit on the support that serves to guarantee the exposure of the knee to the apparatus for nuclear magnetic resonance. In the case in which the diagnostic apparatus is the classic one, the support is the aforementioned bed; in the case in which instead the diagnostic device is that for the extremities of the body only, the support is generally a sort of revolving armchair, which allows the patient to stay in a sitting or semi-sitting position.

In the accommodation on the support provided, the patient receives the help of the (usual) radiologist, who, in the meantime or immediately afterwards, also takes care of providing him with all the necessary comforts (eg: pillows, blankets, earplugs, etc.). .) and to give him the last fundamental instructions for the correct conduct of the exam. Among these indispensable instructions, the absolute immobility to which the patient must adhere during the entire procedure deserves a mention: the body's movements, in fact, jeopardize the accuracy of the images, hence the success of the magnetic resonance in the knee.

At the end of the positioning of the patient, the turning on of the diagnostic machinery and the consequent exposure of the patient to magnetic fields and radio waves can finally take place.

It should be remembered that modern magnetic resonance equipment is equipped with loudspeakers and cameras for communicating with medical personnel, who, as a rule, once the exam has begun, will take place in a room adjacent to where the patient resides. The presence of a communication system ensures complete control of the situation and the possibility, to those who are undergoing the procedure, to report any illnesses or problems (NB: this is more common if the use of the classic is used cylindrical apparatus for magnetic resonance).

Like any type of MRI, even MRI is noisy. This explains why, before turning on the diagnostic machine, the patient receives the aforementioned ear plugs.

The knee magnetic resonance performed with the use of machinery for the ends of the body alone is the ideal solution for people with claustrophobia.

In fact, during its execution, the patient is absolutely not confined to a restricted environment, but is - so to speak - outdoors.

How does the knee magnetic resonance with contrast medium vary in the procedure?

In addition to what has been previously described, the knee magnetic resonance with contrast medium also includes the injection of the contrast medium. The injection of the contrast medium takes place shortly after the accommodation of the patient, a few minutes before turning on the diagnostic machine.

The radiologist is in charge of the injection, in collaboration with a professional nurse.

Generally, the contrast medium used is based on gadolinium .

How long does an MRI scan take?

MRI usually lasts 20-25 minutes .

The use of contrast medium lengthens the time by a few more minutes.

What happens at the end of the exam?

As a rule, immediately after the conventional knee MRI, the patient can get dressed and return home and to his daily activities, waiting for the medical response.

In the event that the contrast medium has been used, the return home can take place only after 1-2 hours from the end of the procedure. This is a completely precautionary measure.

risks

Conventional knee resonance imaging is a highly safe and completely harmless diagnostic for the human body.

The advantage of not exposing the patient to ionizing radiation makes it a test that can be repeated several times, even after a short time.

Risks of magnetic resonance to the knee with use of the contrast medium

Although very rarely, contrast-enhanced MRI procedures - including those that have the subject of a knee investigation - can give rise to adverse effects of varying severity.

The mildest adverse effects include: headache, nausea, vomiting and / or dizziness.

The most serious adverse effects, on the other hand, include: allergic reactions to the contrast medium and systemic nephrogenic fibrosis (*).

* NB: the possible adverse effects of an MRI with a gadolinium-based contrast agent are reported.

Contraindications

The contraindications to conventional magnetic resonance knee resonance are the same contraindications that are registered on the occasion of any other type of magnetic resonance, which does not use contrast media.

Consequently, all those who present, within the human body, devices or fragments of metallic nature, such as for example pacemakers, neurostimulators, splinters (those in the eye in particular) and intracranial clips, cannot undergo the diagnostic examination in question. for a brain aneurysm, hearing aids, metal prostheses, metal sutures, etc.

Knee MRI and pregnancy

For pregnant women, the examination is not recommended during the first 3-4 months of pregnancy; after which there is more freedom.

Contraindications in case of magnetic resonance in the knee with contrast medium

Briefly, in the case of a magnetic resonance to the knee with contrast medium, the following contraindications are added:

The presence of severe renal insufficiency or abnormal creatinine test results ;
The presence of severe liver failure ;
The presence of an allergy against the contrast medium necessary for the examination;
The state of pregnancy .