September 2000

Sonography teams up with MRI in shoulder

By Karen Sandrick

Although ultrasound has been used to evaluate the rotator cuff since the mid-1980s, MRI has generally held center stage for imaging the musculoskeletal system and specifically for identifying injuries in the shoulder and arm. Recently, however, sonography has made a comeback as principal supporting player, armed with new high-frequency probes, better gray-scale processing, and improved image resolution. Sonography also is less costly and more accessible than MRI.

Ultrasound most likely will not topple MRI, however, because it does not visualize some structures in the shoulder and arm and is operator-dependent. Yet sonography is joining the imaging team, particularly for assessing injuries to the rotator cuff and even for ruling out pathology in the labrum.

For imaging the shoulder and arm, ultrasound’s popularity has grown in the U.S. over the last five years. Seven-mHz transducers have been replaced by higher frequency probes that capture anatomy in more exquisite detail. Software packages, such as tissue harmonic imaging, have begun providing better definition of torn and normal rotator cuffs, and power Doppler has increased the detection of inflammatory changes around the biceps tendon.

As a result, radiologists can see abnormalities in athletes that were once impossible to spot, such as a tear or avulsion of the flexor digitorum profundus off the base of the finger. With today’s advanced ultrasound systems, radiologists can locate the site of tendon retraction in the hand, as well as small tissue nodules and adhesions after surgery. Refinements in sonographic scanning technique have improved the exposure of difficult-to-visualize rotator cuff structures that often lie hidden under the acromion.

Dr. Sharlene Teefey, an associate professor of radiology at the Mallinckrodt Institute of Radiology in St. Louis, said that patients are asked to extend the arm and place the hand on a back pocket with the palm on the hip, then move the elbow medially. This position moves the rotator cuff from beneath the acromion and allows better visualization.

Ultrasound works well for imaging full-thickness rotator cuff tears. According to a study conducted by Teefey of shoulders in 98 patients with shoulder pain, sonography achieved a 100% sensitivity, identifying 65 full-thickness tears that were subsequently confirmed by arthroscopy. Sonography detected 17 true negatives and three false positives, for a specificity of 85% and an overall accuracy of 96%. It also predicted the size of tears on the transverse measurement in 86% of the shoulders. The study was published in the Journal of Bone and Joint Surgery in April.

Teefey is now comparing sonography with MRI and, in her first 50 cases, has found ultrasound and MRI to be equally accurate in detecting full-thickness rotator cuff tears. Sonography has not achieved such results with partial tears, but Teefey is exploring ways of improving visualization of these tears, such as injecting fluid into the joint to outline the defect in the cuff.

Sonography is well suited for finding biceps tendon ruptures, dislocations, and subluxations, and it detects fluid or thickening in the bursa, severe synovitis around the biceps tendon, and calcifying tendinitis, Teefey said.

Ultrasound also performed well in a pilot study of the shoulder labrum that compared sonography with arthroscopy in 20 cadaveric specimens. Sonographic and arthroscopic findings correlated in 69 of 80 labral quadrants (86%), said Dr. Jon A. Jacobson, a clinical assistant professor of radiology at the University of Michigan. In the study, ultrasound had a high specificity (99%) and negative predictive value (99%) in differentiating labral tears from normal or degenerated labral tissue. It had only modest sensitivity (67%), however, in identifying actual labral tears.

“Although the numbers were not great, we feel that, for a preliminary study, they show some promise for using ultrasound in the evaluation of the labrum,” Jacobson said. “We essentially showed that you can see the labrum most of the time, and that when the labrum looks normal, it usually is normal. The problem occurs when the labrum appears to be abnormal, and it’s unclear whether the labrum is torn or degenerated. So we’re looking mainly at ultrasound as a possible screening tool to look at the labrum when scanning the rotator cuff, to provide information about the cartilage in the shoulder.”

Sonography does have some major drawbacks, said Dr. David Rubin, an assistant professor of radiology at Washington University, St. Louis.

“Ultrasound is more operator-dependent; it takes longer to learn, and there are fewer people who can perform it correctly than for MRI. Although sonography is an excellent way of looking for a hole in the rotator cuff tendon, it doesn’t provide any information about the quality and amount of muscle atrophy, which is important for orthopedic surgeons to plan treatment,” Rubin said.

Teefey is conducting a study comparing MRI with ultrasound to learn whether sonography can identify muscle atrophy.

But ultrasound has two strengths that make it attractive in these cost-conscious times: accessibility and affordability. The ultrasound clinic at the University of Michigan is right next to the orthopedic clinic, so orthopedic surgeons who are concerned about a rotator cuff tear can send the patient for sonography and get a report within an hour.

“Some private-practice MRI groups have a short turnaround time, but getting quick results can be a problem in large institutions. Given that ultrasound can be as effective as MRI in finding rotator cuff injuries and can provide results quicker for about a third of the cost, that’s hard to beat,” Jacobson said.

Teefey, however, doesn’t see sonography as a substitute for MRI.

“Most of the issues that relate to glenohumeral instability or ligamentous problems are best dealt with by MRI. The big role for ultrasound is for rotator cuff disease and some types of biceps tendon pathology. So we don’t want ultrasound to be viewed as competition to MRI. It can be highly complementary to MRI for evaluating the patient with a painful shoulder,” she said.