I guess I am lucky to have great hearing and a radar sensitive ear for discussion about X-rays and medical problems. The other day my ears perked up as I was sitting in a restaurant eaves dropping on two couples speaking about their total joint replacements and imaging studies. One of them had a knee replacement and the other had a hip replacement. They were chatting about postoperative imaging studies and mentioned that "you know, it is not possible to take an X-ray because of the metal in the new joint." The other woman agreed and added that, "I'm glad I can have an MRI and I was told it won't hurt the machine."
Both statements, although somewhat factual, are not totally accurate. The main question is what detail is needed and what is the most appropriate and cost effective imaging examination for post arthoplasty symptoms of pain or discomfort. On conventional X-ray, hardware alignment, wear and tear, fractures, infection, loosening and osteolysis (a condition of gradual bone loss around hardware) can be evaluated. CT has value in postarthoplasty assessment but is limited by metal beam hardening which may produce artifacts on the image. Nuclear Medicine bone scan can be very sensitive to abnormalities like loosening or infection but is not very specific. Interventional procedures performed under imaging guidance are very helpful to withdraw fluid and/or inject medication which helps to confirm the origin of the discomfort. All these imaging techniques, as well as MR, play a role in diagnosing a painful total joint replacement.
MR can be used to image total joint replacements but some caution is required. In the past many doctors believed that if there is an orthopedic metallic implant in an extremity or joint it could not be imaged with MR, because of the strong magnetic field that would affect the metal implant and/or distort the image and render the examination unreadable. At Hospital for Special Surgery we have conducted research adjusting pulse sequences and parameters of an MR examination performed for a total joint replacement. MRI performed under these circumstances is not only possible but extremely sensitive and specific. MRI, because of its superior ability to image soft tissues, can detect early signs of total joint replacement failure and is now considered to be the ideal method for imaging total joint replacements and identifying sources of pain. The MR results provide a basis for treatment options as it is sensitive to identifying early stages of failure. An appropriately performed MR examination provides the necessary information that allows the doctor and patient to determine potential treatment options that could possibly prolong the life of the replacement hardware and potentially avoid surgical revision or replacement of the existing arthroplasty. MRI is further beneficial for imaging as it does not expose the patient to ionizing radiation.
If you are considering a total joint replacement or currently have one and need imaging to evaluate pain or discomfort, speak with your physician about all of the available imaging options. Know your options and make sure your referring physician knows what information he/she is looking for when ordering an imaging study.