Identifying Cartilage Changes Before They Are Irreversible
Using a parameter unique to magnetic resonance imaging (MRI) may allow for early detection of cartilage changes that occur with juvenile rheumatoid arthritis ( JRA), according to research conducted at Cincinnati Children's. "Cartilage damage is irreversible. So the idea is to recognize changes before you get to that state," explains Tal Laor, MD, section chief of musculoskeletal radiology.
MRI relies on a huge magnet. "When you put somebody in the magnet, all the protons in that person's body line up with the magnet," explains Bernard Dardzinski, PhD, division chief of radiology research and the Imaging Research Center at Cincinnati Children's. "When you disturb that, you produce two relaxation times. T1 is how fast all those protons return to align with the magnet. T2 is how fast the signal decays."
A study among 39 girls, including 18 with JRA, mapped T2 relaxation times on the weight-bearing cartilage of the distal femur. "The overall goal was to see if you could pick up a parameter that might describe changes in cartilage earlier than the typical changes you see on clinical MRI, to pick up microscopic changes before they become big erosions," Dr. Laor explains. The study found that T2 was a useful parameter. The average T2 relaxation times were significantly higher in the girls with JRA than among the healthy girls.
Monitoring Therapy
An imaging technologist helps a teenage girl get ready for an MRI.
A swollen knee is the reason many children are referred for an MRI, which often leads to or confirms a diagnosis of JRA. Unlike conventional radiographs, MRI can provide clear images of tissues other than bones, such as cartilage. MRI used with an intravenous contrast agent to enhance the images can show the inflammation and the effects of treatment on the knee joints. As Dr. Dardzinski explains, "If you treat the inflammation, does that stop the cartilage from being attacked? On MRI, we can actually see if the inflammation is getting better and the cartilage is being preserved."
Those findings led to a study imaging the hands and wrists of children with JRA. "Although the hand is very often affected, it can be a very difficult area to assess clinically," Dr. Laor notes. MRI correlated well with clinical diagnosis, plus MRI showed the inflammation of tendons. This can be an important finding, Dr. Laor says, because "flexor tendons often have disease, but the extent of the disease may be underestimated. The rheumatologists can use this information to help guide therapy."
Tell Them to Rest
A study that Dr. Laor collaborated on with another colleague at Cincinnati Children's, orthopaedic surgeon Eric Wall, MD, has immediate implications for some child athletes and their physicians. The findings apply to children who train and play sports vigorously and whose growth plates have not yet fused, which typically occurs in the early teen years.
The researchers reviewed MRIs that revealed widening in the growth plates of the knee of six high-level child athletes, as well as subsequent MRIs and other data. The five children who complied with a regimen of rest and immobilization improved within three months. A child who continued vigorous tennis training had persistent knee pain and in later years developed malalignment of her knees.
The authors concluded that the significance of these MRI findings should be communicated to referring clinicians and the child advised to rest to promote healing. "The typical course would be to put these injured athletes through physical therapy and progressive rehabilitation, but that is exactly the wrong thing to do," Dr. Laor says.
Tal Laor, MD, is associate professor of radiology and pediatrics. Bernard Dardzinski, PhD, is associate professor of radiology, pediatrics and biomedical engineering. Joint research projects have been reported in the Journal of Rheumatology (32[9]:1811-20, 2005), Arthritis & Rheumatism (50[3]:901-905, 2004) and Magnetic Resonance Imaging (22[9]:1201- 1210, 2004).
