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MRI technology has
changed the way doctors diagnose a variety of injuries and
illnesses. So today we'll conclude this three part series on
musculoskeletal imaging by discussing the MRI and its uses in
sports medicine and orthopaedics.
MRI stands for Magnetic
Resonance Imaging. The technology that allows MRI to produce
images is very complicated. Unlike most of the other
technologies discussed previously, MRI does not utilize X
radiation.
In a nutshell, there is
an extremely strong electromagnet that is cycled on and off. As
this happens, some of the molecules, atoms, and portions of
atoms move into different polarities. The computer can take
these polarity changes and translate them into images that very
accurately demonstrate the anatomy of the area being scanned.
The quantum mechanics
principles that are applied in MRI technology have been around
for quite a while but their everyday application to medicine has
only been evident and practical for around a decade or so.
Since there is a very
powerful magnet used, several precautions must be taken when a
patient is scanned in an MRI machine. First of all,
ferromagnetic objects can't be taken near the scanner. Also,
people with implanted devices like pacemakers or automatic
internal defibrillators can't be imaged with MRI.
Also, people in certain
fields like welding and metalworking must be especially careful.
Often times it is necessary to get a preliminary CT scan of the
face and orbits to make sure that people in these fields don't
have tiny pieces of metal in their eye that might be attracted
to the magnet.
And, of course, people
who know that they have a metallic foreign body like a bullet
can't go inside the MRI scanner.
With all of those
caveats aside, the MRI scanner can provide very useful
information about the area being scanned.
Magnetic resonance
images provide excellent detail of the soft tissues being
scanned. Unlike traditional X rays or CT scans which provide
some soft tissue definition but excellent bone definition, MRI
is just the opposite.
Sports medicine doctors
have been using MR imaging since its inception. For example,
when an athlete injures their knee and the clinical picture is
confusing for one reason or another MRI can often provide the
answer.
With MRI pictures, the
structures within the knee that can't be seen with X rays can be
visualized. The ligaments and cartilages within the knee can be
evaluated and their integrity can be assessed.
Sometimes in sports
medicine, time is of the essence. In these cases when the
diagnosis would likely be apparent with time and conservative
treatment but an answer is needed quickly, MRI can help. The
injured structures can be visualized immediately and a diagnosis
and treatment plan can be formulated immediately after the
images are reviewed.
MRI is also very useful
in the shoulder. Sometimes it is necessary to visualize the
rotator cuff tendon to see if there is a full versus partial
thickness tear. MRI is fairly good at determining this, which is
important since the surgical management can be very different.
MRI is the sine qua non
of visualizing soft tissues within and around the spinal column.
People who've experienced much back or neck pain have likely had
an MRI scan. Virtually all operations that take place on the
back or neck do so after and usually based upon an MRI scan.
MRI also has occasional
uses in the hip, ankle, wrist, and elbow. However, since the
soft tissues within these joints are more limited and the
anatomy can be seen pretty well with plain radiographs, its use
is more limited.
With all of the wonders
of MRI, it should be kept in mind that it's not perfect. Indeed
MRI can miss a wide variety of clinically significant injuries.
An example might be a torn meniscus cartilage within the knee.
MRI is between 85% and 95% sensitive for diagnosing this injury.
Therefore, it is important not to let MRI findings obscure a
fairly obvious clinical diagnosis.
MRI is now a routine
tool used in the diagnosis and treatment of sports medicine
conditions. And although it is important and necessary
instrument, we shouldn't lose sight of the fact that most
diagnosis are still made the old fashioned way with history,
physical examination and X ray.
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