Radiology tests, such as an xray and MRI, have become a crucial component for diagnosing sports injuries. In fact, I always tell people that the two fellowship-trained musculoskeletal radiologists where I work are among the most important components of our sports medicine program, giving us what I consider to be state-of-the-art ability to diagnose the most difficult of sports injuries. In recent years, the use of specialized tests, especially magnetic resonance imaging, has evolved from imaging used mainly by specialists such as orthopaedic surgeons, to use among primary care providers as well.

Use of xray and MRI by primary care doctors

In the September-October issue of the journal Sports Health, David J. Petron et al. present a case control study looking at whether or not primary care providers overutilize magnetic resonance imaging. They retrospectively looked at 100 patients older than 40 years old with chronic knee pain referred by primary care providers who had ordered MRIs of the knee after seeing those patients. Primary care physicians of multiple specialties, nurse practitioners, and physician assistants evaluated these patients. The authors looked at how many of the 100 patients had plain x-rays of the knee performed by primary care providers. Within the group that had x-rays, the authors studied how many of those were weight-bearing x-rays, and specifically flexion weight-bearing x-rays. They also looked to see how many of those patients had their treatment plans altered as a result of the MRIs. Finally they determined whether or not the orthopaedic surgeons would have ordered the MRIs if they had seen the patients first.

In this study, the authors determined that of the 100 patients with knee MRIs ordered by the primary care providers, only 44 had undergone plain x-rays of the knee. Of those 44 patients with x-rays, only 24 of the x-rays were weight-bearing films, and of those only seven were flexion weight-bearing x-rays. 76 of the 100 patients’ treatment plans were altered after the MRI, with the vast majority of those changes involving referral to an orthopaedic surgeon. When included with the 24 patients whose treatment plans were not altered by the MRI, 90 of the 100 patients’ treatment plans were either unchanged by the MRI or the patients were referred to an orthopaedic surgeon.

Based on the history and physical examination findings, the orthopaedic surgeons determined that they would have only ordered 12 of the 100 knee MRIs ordered by the primary care providers. They felt that they would not have ordered an MRI of the knee for any of the patients 60 years or older in the study. Therefore, the authors concluded that primary care providers had underdiagnosed osteoarthritis and degenerative changes by x-rays and utilized MRIs too frequently.

Do doctors order an MRI too frequently?

This might be a complicated study for a non-medical person reading this post. I will try to summarize this in basic language, as this topic comes up very frequently in the office. Many times a day in clinic I will have a patient referred by their primary care provider with either non-weight-bearing x-rays of the knee or only an MRI. Patients get confused when my medical assistant tries to get x-rays in our office prior to me seeing them, as the patients will then say that they’ve either had x-rays or had what they feel is a better test, namely the MRI. And for those who don’t understand the difference between x-rays and MRIs, x-rays just show bones, while MRI’s show all structures, including the tendons, ligaments, cartilage, and the menisci, but they are also much more expensive.

Arthritis on X-ray and MRI

Here’s the problem. Osteoarthritis is a common problem in adults over the age of 40. In basic terms, the articular cartilage (or the cartilage lining the ends of the bones) starts to wear out. As this degeneration happens, the space between the bones starts to narrow. Non-weight-bearing x-rays often do not show the true extent of arthritis because gravity and the patient’s weight do not compress the femur and the tibia together. Often weight-bearing x-rays, especially weight-bearing x-rays with the knee flexed, will show much more joint space narrowing than non-weight-bearing x-rays. Along the same lines, MRIs are performed with the patient lying down. The MRI can demonstrate degeneration of the articular cartilage, but again without weight bearing, the true joint space narrowing is probably underrepresented.

X-ray showing degenerative arthritis of the knee
Note the bone-on-bone joint space narrowing seen on flexion weight-bearing x-rays

The other problem is the distinction between pain from osteoarthritis and pain from a meniscus tear. The meniscus, unlike the articular cartilage lining the ends of the bones, is a C-shaped piece of cartilage that serves as a shock absorber between the femur and the tibia. Unfortunately in older adults, both a degenerative meniscus tear and osteoarthritis can coexist. If you think about it, this concept makes sense from a mechanical standpoint. If the space between the femur and tibia is decreasing due to articular cartilage breakdown with osteoarthritis, it makes sense that the structure between the bones, namely the meniscus, gets damaged.

Meniscus tear on xray and MRI

This distinction between a meniscus tear and arthritis is important from both a diagnostic and treatment standpoint. Typically, pain from a meniscus tear is treated with arthroscopic surgery. The surgeon looks in the knee with an arthroscope and uses scissors and a shaver to trim out the part of the meniscus that is torn. Results from the surgery in terms of pain relief are usually very good. Treatment for osteoarthritis usually does not involve surgery, focusing on anti-inflammatory medications, cortisone or viscosupplementation injections, braces, weight loss, physical therapy, canes or other assistive devices, etc.

Shaver trimming out a meniscus tear
While the shaver is trimming out part of the torn meniscus, note the irregular nature of the cartilage on the femur above the shaver.

The problem comes with a patient with both a degenerative meniscus tear and osteoarthritis. We know from two landmark studies done over the last decade, for one of which I did an interview with the Associated Press when it was published, that arthroscopic surgery to “clean up” articular cartilage damage (osteoarthritis) is not very successful. In fact it shows no significant improvement in pain relief compared to placebo surgery two years after the surgery. From an orthopaedic surgeon’s standpoint, the key when evaluating patients over 40 is to determine if the pain is coming more from the meniscus tear or from osteoarthritis, as pain that seems to be coming from the meniscus tear responds well to surgery.

That gets us back to the issue of x-rays and MRI. If flexion weight-bearing x-rays show significant joint space narrowing, it really doesn’t matter if the patient has a degenerative meniscal tear. I will note that it’s unlikely that surgery will significantly improve the patient’s pain. I am honest with patients before surgery, telling them that the portion of their pain that is coming from the meniscus tear will be better after surgery. Unfortunately they may have some pain after surgery related to the arthritis, which “cleaning up” the damaged articular cartilage likely will only give short-term relief.

The authors of this study do offer reasons as to why primary care providers order MRIs even before obtaining x-rays, and I understand them. First of all, many primary care physicians do not have x-ray capability in their office. They feel that if the patient has to go to another facility for x-rays, they might as well get an MRI instead. Also, the PCPs might not know to order the correct x-rays. By no means am I being critical of primary care providers, as they have to know about every organ system in the body and a ridiculous number of medical illnesses and treatments. When I give talks regarding evaluation of sports injuries to primary care providers, I include a list of specific x-rays to order if they are going to order x-rays. I don’t expect that the doctors will remember the list, but I encourage them to give the list to their x-ray techs to use when they order the x-rays. Hopefully this effort will decrease the number of MRIs ordered and will prevent a patient from getting non-weight-bearing x-rays in their offices and then getting another set of x-rays in my office. And I encourage the primary care physicians, if they are going to refer the patient to an orthopaedic surgeon anyway, to hold off on ordering an MRI and let me (or any orthopaedic surgeon) to determine if an MRI is needed at all.

Take home message

So what is the take-home message from this study? As health care has evolved, patients are required to see their primary care physicians first much more often than being able to initially see specialists. This trend places more of a burden on the primary care physicians to diagnose and treat a wide spectrum of diseases. Also, there is the issue of health care costs. X-rays of the knee cost between $50 and $150. An MRI can cost between $1000 and $2000. In adults over 40, where osteoarthritis is so prevalent, utilizing appropriate x-rays can limit it the need for a large number of the MRIs, as this study has shown. A patient can discuss the appropriate test with the their primary care physician. If the physician is uncomfortable in ordering a test, direct referral to an orthopaedic surgeon who can make the determination of the appropriate test might be useful to make the appropriate diagnosis and save health care dollars.

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Read all three part of this series.
X-rays vs. MRI’s, Part 1 of 3: Do I really need x-rays?
X-rays vs. MRI’s, Part 2 of 3: Do I need an MRI?