MRI stands for Magnetic Resonance Imaging.  As the name implies, it is a way to image (look inside) the body using magnetic fields (and radio waves). Unlike traditional imaging modalities, such as x-rays and CT scans, there is no exposure to ionizing radiation. Also, MRI is far superior to older imaging modalities when it comes to visualizing soft tissue structures.  Bony detail is usually better delineated with x-rays and CT scans, although MRI can give some additional information regarding the internal structure of bones.

MRI does have limitations, however.  The magnetic field can become distorted around metallic objects, so metallic implants such as screws and artificial joints make the MRI picture blurry in the vicinity of the implants.  Current metallic surgical implantable devices are typically made of stainless steel or titanium alloy, both of which are not magnetic metals.  However, shrapnel imbedded in the body can be tugged at by the strong magnetic field required for MRI.  Such tugging on shrapnel in most locations causes no problems.  However, shrapnel consisting of magnetic metals in certain sensitive locations can lead to problems if placed in strong magnetic fields.  Also, implanted electronic devices such as pacemakers can have their function affected by magnetic fields.  It is therefore important for patients to inform their physicians and imaging technicians if they have had any such devices, or if they think they may have shrapnel from previous injuries, prior to undergoing MRI.

Also, it is important to remember that no imaging modality is 100% accurate, including MRI.  This tests, while noninvasive, is not as good as direct observation of tissues during surgery.  The accuracy of MRI varies with the structures being imaged.  Also, the clarity of the pictures generated by MRI depends to a large part on the machine used, the software used, the proficiency of the imaging technician, the imaging protocols, and the degree to which a patient cooperates by being as still as possible during the imaging process.  Lastly, an area that has undergone previous surgery is altered by the surgical intervention, making MRI diagnosis less reliable than it would otherwise be.

Traditional MRI  machines have been termed "closed", and look like long tubes into which people are slid using a moving gurney. Some people are too claustrophobic to tolerate this without sedation.  Open MRI machines avoid the tube, but in the past have resulted in image quality substantially poorer than closed machines.  However, recent advances in magnetic field generation and imaging software has led to the development of open MRI machines with image quality rivaling that of traditional closed machines, while avoiding the feeling of being confined in a tight space.

MRI is a valuable tool that, if used correctly in concert with other information, can help diagnose structural problems in the body.  Its main use in Sports Medicine is to help determine if a structural problem requiring surgical intervention is likely present.