Updated December 16, 2014.

Magnetic resonance imaging, or MRI, is a very useful tool for an orthopedic surgeon. An MRI is helpful at diagnosing many common orthopedic problems. However, an MRI may not always be necessary, and may not be helpful in some situations. Patients are sometimes upset if their doctor does not order an MRI, and may feel as though they are getting inadequate medical care.

There are several reasons why your doctor may not have ordered an MRI, hopefully some of these can be explained here.

• An MRI is not always the most accurate test
  Obtaining an MRI is useful in the diagnosis of many conditions, but not in all. For example, the sensitivity of an MRI in diagnosing an ACL tear is about 90%; that means that 10% of ACL tears will not be seen on MRI. The sensitivity of finding an ACL tear on physical examination by an experienced orthopedic surgeon is also about 90%. Therefore, it may not be necessary to obtain an MRI if the diagnosis can be just as reliably made by other methods. This is especially true of problems which MRI is less helpful than other methods of diagnosis.
• An MRI may not be helpful at all
  MRIs are not helpful for some conditions, such as advanced arthritis of the knees or hips. In these conditions it is true that the MRI would show abnormalities, but these abnormalities are much better illustrated on regular X-rays. MRIs are not better than X-rays, bone scans, or other tests... an MRI is simply another test; the MRI may be more useful in some situations, and less useful in others. Part of being a good orthopedic surgeon is knowing what the right test is in a given situation; an MRI may not always be the right, or the best, test.

• An MRI is often not the first step
  Treatment of most orthopedic conditions is step-wise. Usually treatment begins with simple steps in an effort to solve the problem with as little disruption to the patient as possible. As treatment progresses, so does the diagnostic investigation. This is the way to solve problems. Ordering every possible test during an initial evaluation may be necessary in some situations, but is not a prudent way to proceed in most cases. Ordering unnecessary tests early in treatment can cause more trouble and confusion, and may even delay the right treatment, rather than proceeding deliberately and logically.
• An MRI is only a diagnostic tool, not a treatment
  An MRI gives some people peace of mind, but will do nothing to change the symptoms of your condition. Many people say "I need an MRI because it still hurts." Keep in mind, the problem does not change because an MRI is done. It is true that an MRI may help guide treatments, but, as described above, an MRI does not necessarily help in all situations.

This is not meant in any way to discourage the use of MRIs or minimize the utility of an MRI. These are incredibly useful tests to be done in the right situation. If you think you need an MRI, ask your doctor. He or she should be able to explain to you why you do, or don't, need an MRI.