Who did an MRI after hip arthroplasty. Are endoprostheses a contraindication for MRI? The composition of modern endoprostheses

What are "artifacts" on MRI scans?

Artifacts (from Latin artefactum) are errors made by a person in the process of research. Artifacts significantly degrade image quality. There is an extensive group of physiological (in other words, related to human behavior) artifacts: motor, respiratory, artifacts from swallowing, blinking, random uncontrolled movements (tremor, hypertonicity). All artifacts associated with the human factor can be easily overcome if a person is completely relaxed during the study, breathes evenly and freely, without deep swallowing movements and frequent blinking. However, in medical practice, cases of using light anesthesia are not uncommon.

At what age can children have an MRI?

Magnetic resonance imaging has no age restrictions, so it can be performed on children from birth. But due to the fact that during the MRI procedure it is necessary to remain still, the examination of young children is carried out under anesthesia (surface anesthesia). In our center, the study under anesthesia is not carried out, so we examine children only from the age of seven.

What are the contraindications for MRI?

All contraindications to MRI can be divided into absolute and relative.
Absolute contraindications for MRI are the following features of the patient: the presence of a pacemaker (heart pacemaker) and other implantable electronic devices, the presence of ferrimagnetic (iron-containing) and electric stapes prostheses (after reconstructive operations on the middle ear), hemostatic clips after operations on the vessels of the brain brain, abdominal cavity or lungs, metal fragments in the orbit, large fragments, shot or bullets near the neurovascular bundles and vital organs, as well as pregnancy up to three months.
Relative contraindications include: claustrophobia (fear of closed space), the presence of massive non-ferrimagnetic metal structures and prostheses in the patient's body, the presence of an IUD (intrauterine device). In addition, all patients with magnetically compatible (not ferrimagnetic) metal structures can be examined only after a month after the surgical intervention.

Do I need to have a doctor's referral to get an MRI?

A doctor's referral is not a prerequisite for visiting an MRI center. Your concern for your health, your consent to the examination, as well as the absence of contraindications for an MRI is important to us.

I get headaches often. Which area should have an MRI?

Any person is familiar with a headache, but if it recurs suspiciously often, of course, this cannot be ignored. We recommend that a patient with severe headaches undergo an MRI of the brain and its vessels. In some cases, this may not be enough, because the cause of headaches is not always associated with the pathology of the brain. Headaches can be the result of cervical osteochondrosis, so our specialists additionally advise to undergo an MRI scan of the cervical spine and neck vessels.

How long does an MRI exam take?

The average duration of one study in our center is from 10 to 20 minutes, however, it all depends on the changes detected: sometimes, to clarify the disease, the radiologist can extend the study protocol and resort to the use of contrast enhancement. In such cases, the study time is increased.

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Planning and monitoring the results of hip arthroplasty using computed tomography and magnetic resonance imaging

Recently, in traumatology and orthopedics, there has been a wider introduction into everyday clinical practice of such highly informative radiation methods as computed (CT) and magnetic resonance imaging (MRI). In the present work, we analyzed the effectiveness of using CT and MRI in tanning and monitoring the results of hip arthroplasty. In the preoperative period, CT was performed in 53 patients, and MRI - in 37 patients. Of these, in 34 cases a comprehensive examination was carried out using both methods.

As a result of the analysis of the obtained data, the following conclusions were made. The use of CT when planning a surgical intervention allows more accurate assessment of the bone structure and dimensions of the acetabulum, proximal and distal parts of the femur, to identify the location and size of cystic cavities, bone defects and other pathological changes. The use of MRI helps to clarify the diagnosis, as well as visualization of soft tissue structures and the location of the main neurovascular formations. It should be noted that early signs of aseptic necrosis of the femoral head were identified in 7 cases using MRI, despite the fact that, according to CT, no pathological changes were detected.

In the postoperative period, only CT was performed to control the correct location of the endoprosthesis components (in 21 patients after hip arthroplasty). Using a special protocol for sequential axial sections at 5 levels, the location of the components of the hip joint endoprosthesis was clarified. The acetabular component was located at an average angle of 42 to 60°, with an anteversion of 8 to 23°. When assessing the location of the femoral component, it was found that in most cases the implantation of the endoprosthesis stem was satisfactory. Only in 1 observation was noted a slight varus deviation from the longitudinal axis of the femur by 3°. In addition, functional CT was performed in 9 cases to clarify the strength of fixation of the femoral component and early diagnosis of the development of instability. Functional CT was performed according to the following technique. After constructing a standard skiagram, a set of sections was made at the level of the femoral component and at the level of the femoral condyles. At the same time, sections were made in three series: with the neutral position of the lower limb, with external and internal rotation. After that, the deviation of the axis of the femoral component was measured in comparison with the condyles in all three series of sections.

As a result of the analysis of the obtained data, the following conclusions were made. CT allows a more accurate assessment of the size and structure of the bone tissue, which undoubtedly helps to plan the operation more correctly. MRI should be performed, if possible, in all patients for an earlier diagnosis of aseptic necrosis, even with a negative tonic reaction, which corresponds to the pathomorphological process of lipoid degeneration. According to the qualitative study of these muscles, a significant difference was also found in the pattern of location, density of foci of muscle dystrophy, their predominant localization, the state of the fascia, epi- and perimysium.

A. N. Bogdanov, S. A. Borisov, P. A. Metlenko
Military Medical Academy. S. M. Kirova, St. Petersburg State Healthcare Institution "City Hospital No. 26", St. Petersburg

It is widely believed that people with implants should not have an MRI. In fact, this was the case several decades ago, when patients were given prostheses made of steel, nickel and cobalt. In those years, magnetic resonance imaging could cause serious harm to human health.

TBS implant.

Let's be clear from the outset that people with endoprostheses, pins, screws, fixation plates, breast and dental implants CAN have an MRI.

What implants can be used for MRI

MRI is allowed for people who have had a hip or knee replacement. It is important that the endoprosthesis or fixator for osteosynthesis be made of metals or ceramics with low magnetic susceptibility. This avoids displacement or overheating of the structure during the examination.

Endoprosthesis of the knee joint.

People with hernia meshes, dental, thoracic and joint endoprostheses are also allowed to have an MRI. All these implants are made of materials that do not interact with the magnetic field. This makes the study safe. However, before an MRI, you should consult with a specialist. The doctor will assess the possible risks and recommend the necessary precautions.

Interaction of different metals with a magnetic field

Different metals tend to interact differently with magnets. Some of them are attracted to it, others are repelled, others do not react at all. For the manufacture of endoprostheses, all three types of metals are used.

Table 1. Classes of metals.

The composition of modern endoprostheses

All plates, pins and endoprostheses used in modern traumatology and orthopedics consist of various alloys. Note that different implants contain different amounts of paramagnets and ferromagnets. It is on the composition that the properties of each endoprosthesis, pin or plate depend.

Not all dentures are 100% metal. Most of them contain ceramics or polyethylene. The latter do not interact with the magnetic field, therefore, it does not affect the MRI results and the course of the procedure in any way. However, ceramics most often contain aluminum oxide, which still has a certain magnetic susceptibility.

Destroyed components of the hip joint implant.

Possible combinations of materials in endoprostheses:

• ceramics + polyethylene;
• metal + polyethylene;
• metal + ceramics;
• metal + metal.

Fact! Plates and pins for fixing bone fragments are made of metal alloys. The same applies to external fixation devices (such as Illizarov) and clips that are placed on the vessels.

Composition of artificial joints:

• cobalt;
• chromium;
• molybdenum;
• titanium;
• zirconium;
• tantalum;
• niobium.

After reviewing the composition, you can understand how it will behave in a resonant tomograph. The magnetic properties of each endoprosthesis are determined not only by the material from which it is made, but also by its shape and size. Steel pins and plates longer than 20 cm can be heated above the permissible limit.

Fact! Products containing a large amount of nickel and cobalt interact especially actively with a magnetic field. This means that diagnostics with such endoprostheses should be performed with extreme caution.

Manufacturing companies

Over the past 20 years, implants made of chromium-cobalt alloys have been mainly used in medicine (as we have already found out, these metals actively respond to a magnetic field). There are many models on the market that are made from higher quality materials. They are better tolerated by patients, do not cause allergies and MRI problems.

Table 2.

If you have a prosthesis from one of the companies listed in the table, you can do an MRI without the slightest fear. However, you should not undergo a study without first consulting a doctor in any case.

Contraindications to the procedure

If prostheses, pins and plates are firmly connected to the bone tissue and cannot move, then implants of other localization can easily move under the influence of a magnet. Therefore, it is STRICTLY PROHIBITED to conduct magnetic resonance imaging in their presence.

Implants, in the presence of which it is impossible to do an MRI:

• artificial heart valves;
• stents and clips on vessels of any localization;
• middle or inner ear implants;
• pacemakers;
• artificial lens;
• Illizarov apparatus;
• insulin pump;
• large metal implants.

How to know if you can get an MRI

Remember that you can do an MRI with the permission of a specialist. Only he will determine whether you need this study and whether it will harm you. Perhaps the doctor will make a diagnosis without magnetic resonance imaging. Spondylosis of the spine and deforming osteoarthrosis of II-IV stages can be detected using conventional radiography.

Comparison of visual diagnostic methods. MRI is on the right.

Possible complications and precautions

MRI in the presence of electronic implants can seriously harm a person or even lead to his death. Performing a study on people with coronary walls and clips on the vessels of the brain can provoke massive bleeding, which will be fatal. Implants made from some alloys may move out of place or heat up during an MRI scan, causing burns.

MRI setup before the procedure.

People with certain types of implants are strictly prohibited from doing magnetic resonance imaging. But patients with implants made of "dangerous" alloys can still try to perform a study. As a precautionary measure, a button is placed in the person's hand. If he feels a strong burning sensation, then he presses on it, and the study is stopped.

Fact! Metal prostheses tend to "glow", making the image of nearby tissues fuzzy. Therefore, it is pointless to try to get an MRI image of the replaced joint or bone, fastened with fonts or plates.

It happens that in people who have undergone surgical operations that entailed the installation of metal implants of significant size in the body, it becomes necessary to conduct such a medical study as magnetic resonance imaging (MRI), while such a study may be associated with a completely different organ where implant was placed. As you know, MRI is a highly sensitive examination method based on the impact of a constant magnetic field of high intensity on a person and the measurement of the electromagnetic response from different tissues. Naturally, the presence of a foreign metal in the body should theoretically make it difficult or even completely undesirable to conduct such a study. Sometimes radiologists motivate their refusal to perform MRI by the fact that a metal implant, being in a high-voltage magnetic field, can heat up, collapse and damage the health of the subject. The behavior of the implant in such a study depends on the material from which it is made, its size and shape. In addition, experts pay attention to the low information content of the image due to the presence of an unnatural tissue pattern.

What is really happening.

Regarding the safety of MRI. Everywhere, including Russia, legislative acts have been adopted regulating the admission to the market of medical products intended for implantation in the human body. They state that all orthopedic endoprostheses and internal fixators (pins, bone plates, screws) must be made of non-magnetic metals and alloys, be inert in a magnetic field and pass the appropriate certification. Therefore, if your implant is certified, then the study should be safe both for the health of the patient and for the implant.

Regarding the low information content of the image, it can be said that in many countries, work was carried out aimed at increasing the informative value of MRI diagnostics. In particular, they resulted in the creation of the MARS (metal artifact reduction sequences) program, aimed at eliminating image distortions and soft tissue and bone artifacts in the area of ​​the hip joint endoprosthesis, arising from the presence of metal implants in the magnetic field.

Summarizing the above, we can conclude that MRI after endoprosthetics or osteosynthesis is acceptable, but we would consider it correct if the decision on the possibility of conducting such a study in each specific case was made by a qualified radiologist based on the documents submitted to him about the implant (certificate on the product, information about the material of manufacture and dimensions), the proximity of the examined organ to the place of implant installation and the possibility of obtaining the necessary informative value of the study.

If a person has undergone surgery, he is interested in whether he can fully live on. In cases where a foreign object is implanted into the body, fears are intensified. So, for example, patients who have implants inserted, a pacemaker installed, will not be able to undergo magnetic resonance imaging if necessary. And is it possible to do an MRI with a hip joint endoprosthesis - also not always.

Magnetic resonance imaging is an examination that allows you to examine in detail the entire human body, or an organ of interest. The procedure is carried out on a tomograph - a device specially designed for this.

Reading information becomes possible due to the influence of electromagnetic waves on the body, as a result of which hydrogen atoms react to magnetic resonance and allow scanning. The computer processes the data and produces a three-dimensional picture, where you can see all the processes that occur with tissues and blood vessels.

The main contraindication to MRI is the presence of metal and electronic objects in the body:

• implants;
• endoprostheses;
• plates;
• staples;
• screws;
• pins;
• clamps;
• fragments.

Endoprosthesis procedure

Sometimes it happens that a joint loses its function, for example, the hip joint. There may be various reasons for this:

• congenital pathologies;
• injury;
• infection;
• oncology.

Modern medicine has learned to replace the natural joints in the human body with artificial ones. The procedure is called endoprosthesis replacement. This is a successful method of returning anatomical functions to the body. The following joints can be replaced:

• hip;
• brachial;

What are endoprostheses made of?

Traumatology and orthopedics have been dealing with the issue of prosthetics of the hip joint for quite a long time. Every year, not only the operations themselves are improved, but also the composition of endoprostheses. Most often, structures are made of alloys:

• gland;
• nickel;
• cobalt;
• titanium.

The ratio in the alloy of different ingredients gives a different response to the impact of a magnet, and quite often critical for the patient, so the presence of such objects in the body as a hip joint replacement may be a ban on MRI.

How do metal objects behave under the influence of a magnetic field?

Each alloy has its own magnetic properties, so the behavior of the hip replacement during MRI directly depends on its composition. However, not only the material plays a role, the shape of the prosthesis itself is also important.

The endoprosthesis of the hip joint under the influence of a magnet can move from the established place, thereby causing unbearable pain. This applies to small items - clips, staples, clamps. The magnetic field can rip them off. As for plates, pins, even a very strong field will not make them move, since the fixation of the element in the bone will be very strong.

Metal structures in the body, such as a hip replacement, can become hot. For example, a steel alloy under the influence of magnetic waves will heat up to a temperature of over 40 ° C, which will burn the joint cavity in which the prosthesis is installed.

If the prosthesis, plate, pin, screw are made of titanium alloys, then computer diagnostics are not contraindicated with such designs, since the magnetic field will not have any effect on them. However, the metal object will give a background and dark spots or blurring will appear on the MRI images.

Before going for magnetic resonance imaging, it is important to find out the composition of your prosthesis or device in the body, and it is best to take a certificate certifying the origin of the product, since the diagnostician will definitely ask her.

Can MRI be performed on patients with a hip replacement?

If it is necessary to do magnetic resonance imaging, and the patient has an endoprosthesis, then it is necessary that there are documents on hand that will indicate information about which implant he has installed, what is its composition and who is the manufacturer. Then, based on the data obtained, the radiologist examines the marking and concludes whether it will be possible to conduct an MRI procedure after arthroplasty.

However, even if the endoprosthesis of the hip joint installed in the patient assumes the presence of a metal exposed to a magnetic field, only those who are to have an MRI of the hip joint, spine, and pelvic organs should be worried. If a tomography of any other limb is prescribed, then the procedure can be safely carried out. Only it should be an open-type tomograph, where the magnetic scanner is located directly above the area under study. The endoprosthesis will not fall into the field of influence of the device and will not give any reaction.

Will a patient with an endoprosthesis be denied an MRI of the spine?

The permission for the MRI procedure also depends on the shape of the installed prosthesis or design. If in the hip joint the plate is shorter than 20 cm, made of titanium, then nothing interferes with the tomography.

However, if the prosthesis contains other metals, or it is a long pin, then in this case the doctor will most likely refuse such a diagnosis, prescribing computed tomography instead. Nothing will happen to the plate, but it will cause a lot of inconvenience to the patient, even during a standard MRI of the spine.

MRI for prosthetics of other joints

Endoprosthetics is a rather complicated operation, after which, for the first year, the patient is under constant control over the behavior of the implant or prosthesis in the body. Immediately after the completion of the surgical intervention, it is worth taking all the documentation with information about which implant was installed, whose production and from which alloy. This may come in handy in the future. As, for example, for magnetic resonance imaging, because no one is immune from this.

Is it possible to do MRI diagnostics with titanium plates - yes, it is quite possible, since they are not magnetic, which means they will not move, heat up, but they can distort the image of the organ, so the decision to conduct diagnostics or prohibit it is made by the doctor. Each specific case is burdened with its own characteristics and aspects, so any procedure and all appointments to it will be purely individual.

If the patient had knee arthroplasty, then problems with MRI can occur only on the lower extremities or on the spine. If the elbow joint was prosthetized, then tomography of the arm will be difficult, regardless of what metal composition the prosthesis had.