Published 9/1/2009
Jennie McKee

Predicting OA after ACL injury

Researchers use quantitative MRI to detect early degeneration

“As orthopaedic surgeons, we pride ourselves on how well we reconstruct the anterior cruciate ligament (ACL),” said C. Benjamin Ma, MD. “And yet, recent studies have shown that degenerative changes develop in the knees of more than 50 percent of patients with ACL injuries, despite surgical reconstruction.”

When the ACL is injured, explained Dr. Ma, the articular cartilage is also damaged. As a result, osteoarthritis (OA) may develop following surgery. He traced the development of OA to the initial trauma experienced by the overlying cartilage on bone marrow edema-like lesions (BMEL).

“This trauma causes potentially irreversible macromolecular damage to the cartilage matrix, leading to cartilage breakdown,” he said.

Although traditional radiographs may not show evidence of OA after ACL reconstruction for a decade or more after surgery, Dr. Ma noted that orthopaedists can use T1rho magnetic resonance imaging (MRI) to detect and monitor early cartilage degeneration.

“Quantitative MRI allows us to look at our results more critically,” he said. “Instead of waiting for 10 or more years to find out how successful the ACL surgery was in preventing arthritis, the surgeon might be able to detect early signs of OA within a year or two (Fig. 1).

“Being able to detect and monitor early OA in these patients may lead to new surgical and pharmacological treatments to combat the disease,” asserted Dr. Ma.

Assessing patients for signs of OA
Dr. Ma’s team evaluated seven healthy volunteers (two women and five men, mean age 33 years) with no diagnosed OA or history of knee injuries and nine patients (four women and five men, mean age 39 years) with acute ACL injuries and BMEL.

MRIs were obtained within 4 weeks of the injury and at 2 weeks, 6 months, 12 months, and 24 months following ACL reconstruction. Researchers then compared the MRI values in cartilage overlying BMEL with values in surrounding cartilage.

“We used the baseline images to define the areas of cartilage overlying and surrounding the initial BMEL, and compared those areas in the follow-up scans to evaluate the biochemical and macromolecular changes that occurred over time,” said Dr. Ma.

BMEL indicate significant damage
Researchers found that BMEL were most commonly found in the lateral tibia and lateral femoral condyles. Nearly 90 percent of BMEL resolved over a 2-year period.

The cartilage overlying BMEL in the lateral tibia was abnormal immediately after injury and continued to be abnormal despite the resolution of the BMEL throughout the 2-year study period.

“We found that the injury was most severe over the superficial zone of the posterior lateral tibia,” said Dr. Ma. “By comparing the overlying cartilage values to the surrounding cartilage values, we were able to assess the severity of each patient’s injury more accurately.”

The results of the study also demonstrated that the medial compartment was initially normal; however, at 12 months, signs of cartilage degeneration were present over the nonmeniscus weight-bearing zone of the medial tibia, despite surgical reconstruction and rehabilitation.

“These results suggest,” explained Dr. Ma, “that the presence of BMEL indicates significant initial damage to the overlying cartilage.”

Dr. Ma reinforced the idea that the use of quantitative MRI to assess patients after ACL reconstruction may cause orthopaedists to evaluate and alter their treatment strategies.

“Quantitative MRI makes us more aware that every ACL injury is not the same—there are different severities of injury to the cartilage,” he said. “Using this diagnostic tool allows us to stratify injuries, which can then dictate treatment. It also enables us to follow the success of these surgeries better than when we rely on traditional radiographs.”

Dr. Ma’s co-authors on “Longitudinal Evaluation of Cartilage Degeneration Following ACL Injuries using Quantitative MRI” included Alexander A. Theologis, BS; Daniel Kuo, BS; Jonathan Cheng, MS; Radu I. Bolbos, PhD; Julio Carballido-Gamio, PhD; and Xiaojuan Li, PhD. Dr. Ma reported ties to Aircast (DJ). His co-authors reported no conflicts.

Dr. Ma presented this study at the 2009 Arthroscopy Association of North America annual meeting and at the 2009 AAOS Annual Meeting.

Jennie McKee is a staff writer for AAOS Now. She can be reached at mckee@aaos.org

Link to e-poster: Longitudinal Evaluation of Cartilage Degeneration Following ACL Injuries using Quantitative MRI