Isn't an MRI a better test for assessing knee pain?
Not necessarily. Many patients have the perception that an MRI is a better test for diagnosing knee problems. That is not true.
Many knee problems are better diagnosed by x-ray, and obtaining an x-ray as the first step is the usual course in diagnosing a knee condition. Knee x-rays give much more useful information about knee alignment, bone quality, and the extent of any degenerative (arthritic) changes within the knee.
An MRI is a useful test as well, but doing an MRI alone won't allow a doctor to get a complete understanding of most knee problems.
What can be seen on a knee x-ray?
You doctor will look for the following on your knee x-rays:
- Soft-Tissue Changes
X-rays are best at showing bone, but there is much more that can be seen on an x-ray. X-rays can show signs of soft-tissue swelling and excess fluid within the knee.
- Bone Quality
X-rays are not adequate to demonstrate bone density (you need a bone density test to detect bone density), but they do show the normal bone architecture. Abnormalities, including certain bone disorders and osteopenia (bone thinning), can be detected on x-ray.
X-rays obtained while standing up can show the alignment of the knee joint and whether or not there is an abnormality in the alignment of the bone. Malalignment can lead to excessive forces on parts of the joint and accelerate arthritic changes.
- Joint Spaces
The space between the bones seen on x-ray is actually filled completely with cartilage. Narrowing of this joint space is the best sign of the extent of knee arthritis.
- Early Arthritis Signs
Other signs of arthritis, including bone spurs, can be seen on x-ray. Some of these early signs offer an indication of how much of your knee pain is due to early arthritis.
X-Rays will show evidence of injury to the bone, including fractures. Not all fractures show up on x-ray, but most do. Common types of fractures seen on knee x-rays include tibial plateau fractures and patella fractures.
An x-ray is a very useful test and helps provide information your doctor can use to make a diagnosis of your knee pain. While this is not as new of a test as an MRI, in some cases it is still a much more useful test. That said, for some conditions, the next step in making a diagnosis, after an x-ray is complete, is to obtain an MRI.
O'Shea KJ, et al. "The Diagnostic Accuracy of History, Physical Examination, and Radiographs in the Evaluation of Traumatic Knee Disorders" Am. J. Sports Med., Mar 1996; 24: 164 - 167.