New techniques improve cartilage imaging

It’s no secret that hip disorders can be devastating—for both patients and society. Degenerative arthritis leading to total hip replacement affects 300,000 people in the United States, and treatment costs over the next 5 years will total more than $8.5 billion.

But in the young adult patient with hip pain, the tendency has been to delay intervention until the problems are severe. In a symposium on cartilage imaging of the hip sponsored by the AAOS and the Orthopaedic Research Society, Paul E. Beaulé, MD, said, “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.”

The most effective strategy for achieving improved results is likely to arise from improved understanding of joint pathology and cartilage deterioration. A major obstacle to better prediction is the limitations of current imaging techniques. But new techniques are making it easier to diagnose cartilage damage earlier, which may result in fewer hip replacements in young patients.

“We need to reduce the incidence of hip replacement in the young patient,” said Dr. Beaulé, “because of the issues of failure, revision, and quality of life.” The issue has come to the forefront, he said, because the accepted set of surgical pathologies has expanded greatly, and now includes osteonecrosis, dysplasia, labral and cartilage tears, and femoroacetabular impingement (FAI), in no small part because of improved imaging techniques.

FAI, he said, “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, Dr. Beaulé said, “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.”

With improved diagnostic techniques and a better understanding of the pathologic process, the goal might shift from not just improving quality of life but “preventing or possibly curing the patient’s osteoarthritis,” Dr. Beaulé said.

He explained that the new generation of imaging techniques does more than simply capture gross morphology. By using biomarkers, a more precise portrayal of joint tissue and pathology can be provided.

“The biomarker is used as a surrogate for cartilage degeneration,” Dr. Beaulé said. “Instead of looking at gross changes, you can pick up what is going on in the joint or in the cartilage now, and what is going to happen over time. If you do something to treat the cartilage, you will see how the cartilage responds. You get a better understanding of whether the hip is functioning or deteriorating.”

The new trio
Panelist Thomas D. Brown, PhD, a researcher, provided an overview 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, 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.

Another 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.

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; in another symposium this week focusing on the hip, 12 percent of the audience named it as the preferred method for assessing articular damage. dGEMRIC measures glycosamino-glycan 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 magnetic resonance imaging (MRI). dGEMRIC can tell you it’s not biochemically normal.”

Femoroacetabular application
Dr. Rakhra noted that over the past decade, femoracetabular impingement (FAI) has been recognized as a major pathogenic factor in the evolution of hip osteoarthritis. Although either the femur or the acetabulum may be 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. It 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).

Fig. 1 A, Apparently normal lateral radiograph of the hip in a patient with FAI. B, Radial sequence MRI scan in the same patient demonstrating significant femoral head-neck offset abnormality, which was not seen on the lateral radiographic view. The arrow indicates an anterolateral head-neck junction cam impingement bump.

Reprinted from Sierra RJ, Trousdale RT, Ganz R, Leunig M: Hip disease in the young, active patient: Evaluation and nonarthroplasty surgical options. J Am Acad Orthop Surg. 2006;16(12):689-703.

Of the various magnetic resonance (MR) modalities, MR arthrography has poor sensitivity, specificity, and accuracy, as well as poor interobserver correlation. The more recently employed high-resolution MRI uses thinner slices and no contrast agent, but has much better values than MR arthrography.

In patients with obvious symptoms of FAI for whom radiographs and MRI scans are normal, the 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.

Prepared by Terry Stanton, senior science writer, AAOS Now.