|Does anyone here know how to take an x-ray?
Contrary to what you might have been led to believe, a vast amount of information can be obtained from x-rays, provided that the appropriate views are obtained and provided that the quality of the pictures is reasonable.
Nevertheless, by and large, patients have poor x-rays taken, and they are then immediately sent for an expensive MRI. It is true that, on occasion, an MRI provides critical nuggets of information that could never have been detected on x-rays. More commonly though, the MRI provides information that can be obtained from a half-decent physical examination and plain x-rays. You might also be surprised to find that plain x-rays can occasionally provide information not found on an MRI. Moreover, as we saw above, it is not uncommon in the setting of knee pain, for the MRI to be frankly misleading.
Unless you are being x-rayed in an orthopedist’s office, chances are that the x-rays obtained will be of the so-called “AP and lateral” type. These two x-rays represent a mug shot of your knee. They are quickly performed and they are inexpensive. They are adequate for detecting major fractures and moderate to severe arthritis. For this reason, these are the views obtained in an emergency room. For many patients, though, these x-rays are inadequate.
Arthritis, by definition, is a wearing down of the cartilage lining the ends of bones. If the wear occurs over a small area, it may be missed. If the x-ray is taken with the patient in a standing position, however, narrowing of the space between the thighbone and the shinbone may become apparent. In such a case, the diagnosis of arthritis is made and an MRI becomes totally superfluous.
In more subtle cases, the location of the arthritis within the knee dictates that the knees be bent during the taking of the x-ray. This has been called the “schuss view”, a crude reference to the position of a schussing skier. If a middle-aged patient comes to me with knee pain, and I suspect subtle arthritis, I will often obtain this view. Again, if narrowing of the space between the bones is detected on this view, the diagnosis is made, and an MRI is completely unnecessary. Compared to the cost of an MRI, a schuss view is practically free.
Arthritis is not the only condition that can be diagnosed by an x-ray. More unusual conditions such as osteochondritis dissecans (OCD) and avascular necrosis can also be detected on an x-ray. These conditions occasionally require a so-called ‘tunnel view’: the patient lies on the x-ray table, and an x-ray is taken with the knee bent about 45 degrees. If you will, this is a schuss view taken with the patient lying down (the tunnel view is easier for the technician than the schuss view). Bone spurs (which are always associated with arthritis) will occasionally lie in parts of the knee only visible on a tunnel view.
In patients under the age of 45, the kneecap is one of the most common sources of knee pain. If, in a given patient, the physical examination suggests that this might be the case, an x-ray can help confirm the diagnosis. Again, inexpensive but appropriate views need to be obtained. These views include a “true” lateral and a Merchant view. A Merchant view (first described by Alan Merchant, MD from California) involves draping the knees over a simple device that is placed at the end of the x-ray table. Without this inexpensive device (it costs just half of one MRI test), it is impossible to make a good assessment of the kneecap’s alignment.
Note that in some patients, arthritis is localized to the kneecap. Only a Merchant view will detect this. Merchant views, therefore, are also worthwhile in patients over the age of 45.