Knees with joint space narrowing lost more cartilage over a year than did knees without joint space narrowing, based on imaging results from a study of 80 adults with knee osteoarthritis.
Previous research has shown that radiography can identify structural osteoarthritis changes in the knee. But whether knees with joint space narrowing (JSN) lose more cartilage than those without JSN over the long term remains unclear.
To evaluate the impact of JSN on cartilage loss, Dr. Felix Eckstein of Paracelsus Medical University in Salzburg, Austria, and colleagues reviewed imaging data from 32 men and 48 women with pain in both knees, medial JSN in one knee, and no (or less) JSN in the other knee (the “less-affected knee”). The patients were selected from the Osteoarthritis Initiative cohort; their average age was 61 years, and their average body mass index was 31 kg/m
The results of the study were presented in September at OARSI's 2008 World Congress on Osteoarthritis in Rome.
Overall, the less-affected knees (with little or no JSN) showed little progression. In the medial tibia, there was little change for knees with no JSN (-1.0%) and a −3.9% change in the less-affected knees with JSN grade 1.
The average change in the tibia in the more-affected knees was −1.6% for the knees with a JSN grade of 1, −2.9% for the knees with a JSN grade of 2, and −6.9% for the knees with a JSN of 3.
When the medial femoral condyle measurements were separated into two parts—weight bearing and posterior—the rate of cartilage loss was greater in the weight bearing than in the posterior part; the tibia increased significantly with worse grades of JSN in the more severely affected knee. The standardized response mean (a measure of change) was significantly greater for JSN grades 3 and 2, compared with 1 for the weight-bearing femoral condyles.
Dr. Eckstein said that he was surprised by the results. “It was thought that subjects with no JSN or small grades of JSN have 'more' cartilage to lose than those at later stages, and would thus progress more rapidly,” he said in an interview. “However, the results showed that the more JSN is present, the faster the cartilage loss occurs.”
The take-home message for physicians is that the cartilage loss is very small in osteoarthritic knees without JSN. “When JSN starts, a vicious cycle of increasing cartilage loss is initiated,” Dr. Eckstein said. The results also suggest that MRI-based measures of cartilage morphometry are particularly responsive at the later disease stages.
The findings should be confirmed in larger cohort studies, which will be possible in the future because the National Institutes of Health-sponsored Osteoarthritis Initiative has recruited almost 5,000 patients, Dr. Eckstein noted.
Dr. Eckstein is co-owner and CEO of Chondrometrics GmbH, a company that provides MR imaging analysis to the pharmaceutical industry and to other researchers.
He also provides consulting services to Merck Serono, Novo Nordisk, Wyeth, and Pfizer Inc., and has received funding from Eli Lilly & Co., Merck Serono, GlaxoSmithKline, Wyeth, and Pfizer.
The image analysis in this study was sponsored by Eli Lilly & Co., and the image acquisition was sponsored by the Osteoarthritis Initiative.
MRI shows full-thickness lesion in cartilage of the medial femoral condyle (yellow). Courtesy Dr. Felix Eckstein