MR imaging offers integral view of articular cartilage repair

Contrary to popular practice, both pre- and postcontrast imaging is necessary for proper MR evaluation of articular cartilage repair, according to new research conducted in Japan. The small study could carry implications for treatment evaluation.

Gadolinium-enhanced MRI has become the preferred noninvasive method to evaluate surgical replacement of damaged cartilage tissue, also known as autologous chondrocyte implantation (ACI). MR's accuracy for gauging glycosaminoglycan concentration provides a reliable indicator of reparative cartilage's quality.

To date, most clinical studies have relied solely on post-gadolinium-enhancement measurements. This method, however, might not be suitable for evaluating reparative cartilage after ACI, according to principal investigator Dr. Atsuya Watanabe, who led a team of orthopedic surgery and radiology experts from Chiba University and the National Institute of Radiological Sciences in Chiba City.

The team came to this conclusion after evaluating knees from nine ACI-treated patients who underwent second-look arthroscopy with biopsy at one year and 1.5T MRI at nearly two years after ACI. Results showed a significant correlation between the compared pre- and postcontrast images and the glycosaminoglycan concentration.

Reparative cartilage in all patients had a lower glycosaminoglycan concentration and a different histologic appearance compared with normal cartilage. Postenhancement measurements alone did not enable detection of glycosaminoglycan concentration differences between reparative and normal cartilage. But comparative measurements did (Radiology 2006;239[1]:201-208).

The study had several limitations, including its small size and the time difference between biopsy and MRI evaluation. The two-hour delay between scan times also raises questions about clinical feasibility. Reimbursement issues pose further hurdles.

But the study results could have implications for expanded clinical applications in different types of cartilage evaluations. Existing methods provide only an anatomic perspective. The technique described by the Japanese researchers, however, could be used for quantitative and qualitative articular cartilage assessments, said Dr. Douglas P. Beall, chief of musculoskeletal imaging at the University of Oklahoma Health Sciences Center in Oklahoma City.

"MR imaging can measure glycosaminoglycan content, which defines articular cartilage's strength. This, therefore, is a noninvasive way of measuring the amount and integrity of the articular cartilage," Beall said.