dGEMRIC leads pack of new biochemical methods

It’s no secret that hip disorders can be devastating—for both patients and society. In the young adult patient with hip pain, the tendency has been to delay intervention until the problems are severe. “The impression is that persistent hip pain in the young adult is an infrequent problem. Early symptoms may be minor and early solutions are difficult,” said Paul E. Beaulé, MD. Dr. Beaulé was part of a symposium on cartilage imaging of the hip held during the 2011 AAOS Annual Meeting and sponsored by the AAOS and the Orthopaedic Research Society.

The most effective strategy for achieving improved results is likely to arise from improved understanding of joint pathology and cartilage deterioration. New imaging techniques are making it easier to diagnose cartilage damage earlier, which may result in fewer hip replacements in young patients.

Femoroacetabular impingement (FAI), said Dr. Beaulé, “is now a recognized cause of hip arthritis, but how we evaluate it and treat it is still in evolution.” Open surgery has been demonstrated to be safe and effective, “but obviously carries significant morbidity for the patient. It is important for us to develop diagnostic tools that give us a better idea of who will benefit from less invasive techniques,” he said.

Improved diagnostic techniques and a better understanding of the pathologic process could shift the goal of treatment from improving quality of life to preventing or possibly curing the patient’s osteoarthritis.

The new generation of imaging techniques does more than simply capture gross morphology. It also provides a more precise portrayal of joint tissue and pathology by using biomarkers.

The new trio
Panelist and researcher Thomas D. Brown, PhD, provided an overview of what he called “the big three” compositional assessment techniques, as well as several others that are “not quite ready for prime time.”

Conventional imaging sequences, he noted, allow visualization of structural changes. “Compositional imaging is another story entirely,” he said, which depends on the composition of the cartilage tissue. Techniques are evolving for segmenting cartilage and delineating its margins. Both manual and automatic segmentation techniques can be used to determine the boundaries of the cartilage.

Orthopaedic surgeons are familiar with T2-weighted magnetic resonance images (MRI), but new imaging techniques enhance these images to show changes in the characteristic of the cartilage matrix. “This is nice for showing early-stage degeneration,” Dr. Brown said.

A second technique, which Dr. Brown described as “an entirely different animal,” depends on the interaction between water and the macromolecular environment. But it requires special programming and is not yet commercially available.

The third of the new “biochemical imaging” technologies, dGEMRIC (delayed gadolinium-enhanced magnetic resonance imaging of cartilage) is the first to gain a foothold in clinical practice. dGEMRIC measures glycosaminoglycan content, and, Dr. Brown said, there is good correlation with mechanical stiffness.

Another panelist, Kawan Rakhra, MD, FRCPC, summed up the utility of dGEMRIC this way: “The dGEMRIC picks up the amount of changes in the glycosaminoglycan. When you have arthritis, you lose that from hyaline cartilage. The cartilage looks the right thickness and looks normal on radiographs and on standard MRI. dGEMRIC can tell you it’s not biochemically normal.”

FAI application
Dr. Rakhra noted that over the past decade, FAI has been recognized as a major pathogenic factor in the evolution of hip osteoarthritis. Whether the femur or the acetabulum is affected, the result is the same: abnormal interaction of bones and articular surfaces and increased biomechanical stress. Complications include labral tear, cartilage injury, and premature osteoarthritis.

In FAI cartilage injury, chondral damage is the marker—the evidence that an underlying pathologic process is ongoing. The status of the cartilage influences therapy, Dr. Rakhra said, as well as prognostic value.

Radiographs are primarily used to diagnose cartilage abnormalities, with the focus on the joint space. Radiographs may be useful with moderate to severe osteoarthritis, but in situations with moderate or very focal chondral changes, radiographs are ineffective, and MRI is indicated. MRI allows direct visualization of hyaline cartilage and can localize and characterize fissures, thinning, full-thickness defects, and delamination. MRI is also comprehensive and can detect a number of injuries and deformities in FAI (Fig. 1).

In patients with obvious symptoms of FAI for whom radiographs and MRI scans are normal, dGEMRIC and other new imaging techniques may be useful. Studies have found that dGEMRIC indexes are reduced in FAI patients compared with controls in all zones of the joint. In addition, dGEMRIC is sensitive to zonal variations in cartilage injury and much more sensitive than standard MRI.

In FAI, dGEMRIC can detect biochemical changes even before morphologic changes occur. “This may lead to a shift in the therapeutic management of FAI, from palliative to more preventive and disease-modifying techniques,” said Dr. Rakhra. “Advanced cartilage mapping will allow for development of MRI-based biomarkers to aid in FAI characterization, prognostication, and monitoring response to therapy.”

Disclosure information: Dr. Beaulé—Wright Medical Technology, Smith & Nephew, Corin USA; JBJS-American; Dr. Brown—Smith & Nephew, JBJS-American; Dr. Rakhra—no conflicts.

Terry Stanton is the senior science writer for AAOS Now. He can be reached at tstanton@aaos.org