Orthopedic implants, materials and devices and their interaction with MRI

Orthopedic implants, materials and devices and their interaction with MRI


Orthopedic installations, materials and devices and their interaction with MRI

The most part of orthopedic installations, materials and devices analyzed in order to verify if magnetic resonance problems subsist, are made by not ferromagnetic materials, and, as a consequence, they are safe, or “MRI conditional” on the basis of specific conditions requested for the patients exposed to MR procedures.

However, in some cases, because of the driving ring  length or formation, the heating correlated to MRI, could be a problem for some orthopedic installations, for fastening devices especially cervical or for the exterior fastening system.

The Perfix disturbance screw used for anterior cruciate ligament reconstruction it’s been recognized highly ferromagnetic.  

Since this disturbance screw is firmly inserted in the bone for his specific application, it’s kept in position with enough power to avoid any movement or change of position.

Patient with Perfix disturbance screw are exposed to magnetic resonance procedures that use MRI systems operating a 1.5 Tesla in complete safety.

Patients with orthopedic installations “safe MR” or “conditional MR”, indicated in the underlined list,have been exposed to magnetic resonance procedures (that use a 3 Tesla or less MR operating systems) without accidents.

Exterior fastening systems. The exterior fastening systems specifically planned frames, clips, poles, pole-pole joint, linchpin, posts, fastening elements, fastening bolts, washers, nuts, hinges, wall sockets, connection planks, screws and other components used in orthopedic and reconstructive surgery.

The indications for the exterior fastening systems are various and include the following treatment applications:

-the opened and closed fracture’s fastening;

-long bones’ pseudo arthrosis  (both congenital and acquired);

-bone lack or soft tissue correction;

-bone deformity or soft tissue correction.

 

The evaluation of the magnetic resonance problems for the exterior fastening system is particularly difficult because of the myriad of possible components (many of them are made of driving materials) and the many configurations used for this devices.  The fundamental concern is tied to MRI heating that depends on exterior fastening system’s particular perspectives (for example the length of the component parts). It’s important to underline that the magnetic resonance conditions (static magnetic sector’s strength, RF sector, RF transmission bobbin, impulse’s sequence, the reclaimed part of body, the fastening device’s position compared to RF transmission bobbin) used, have an outstanding impact on a patient security with an exterior fastening system that get scanned.

To guarantee the patient’s security, the guide lines are generally applied case by case and, as a consequence, the MR professional need to make reference to the label approved by US Food and Drug Administration for a specific exterior fastening system.

It’s important to notice that MRI conditions that result acceptable get applied just to specific configuration used for the judgement of a given fastening device.

Every other configuration could be dangerous.

 

VIBRATIONS ASSOCIATED TO MR PROCESS. Graf et al. has shown that the pair which acts on metal systems because of  the induction caused by parasitic streams with the RM, can be notable. The biggest systems (like fixing devices) achieved with good driving materials, are particularly damaged. It has been proved that the gradient's commutation produces a fast alternated pair. Significant vibrations in more decentralized positions of metal parts can explain why some patients  with metal devices report that they feel a warm sensation during RM exams.

 

MRI SIMULATIONS AND ORTHOPAEDIC DEVICES. Since orthopaedic prothesis tend to have a variety of dimensions and shapes, it's hard to evaluate the MRI heating correlated with those devices.

An efficient method dealing with this problem is to manage a MRI simulation to predict the case of MRI worst heating induced for a determined orthopaedic device of different dimensions in conditions 1.5-T / 64 MHz e 3-T / 128-MHz and then to employ an experimental test to confirm the numerical results for the worst case of heating,  as explained by  Liu, et al. (2013).

 

MRI WITH 3 TESLA AND ORTHOPAEDIC SYSTEM, MATERIALS AND DEVICES.  A great variety of orthopaedic systems has been evaluated because of  their interactions with 3-Tesla magnetic field. The majority of  these are considered passable for the patients  on the basis of  results concerning deviation, and pair edges and their function in an alive practice. For some of the orthopaedic system, the heating linked to the MRI has been evaluated as difficult for some devices, fixing devices (especially external) and cervical fixing devices.

Health MR experts are invited to contact their own producer to obtain the latest information about these devices in order to ensure the patient's safety than the use of MR process.