Musculoskeletal ultrasound (MSK US) is being used more and more outside of radiology, according to a new study published in the Journal of the American College of Radiology.

The authors analyzed Medicare fee-for-service enrollee data from 2003 to 2015, recording the volumes for both MSK US and MSK MRI.

The researchers found that the volume of MSK MRI increased from more than 738,000 in 2003, to more than one million in 2015, an overall increase of 53 percent. Most of that growth occurred between 2003 and 2007, and growth was relatively stagnant until 2015. Radiologists maintained 93 percent of MRI share in 2015 and were followed by orthopedic surgeons at 5 percent.

The volume of MSK US increased from more than 96,000 in 2003 to more than 429,000 in 2015, an increase of 347 percent. However, the radiologist market’s share decreased from 65 percent in 2003 to just 37 percent in 2015. Nonradiologists are now performing a majority of all US exams.

So what led to MSK US rising so much more than MSK MRI? The authors had one idea.

“Growth in MRI may have been suppressed by the activities of the radiology benefits management companies, which tend to limit MRI use but not that of US,” wrote lead author Riti M. Kanesa-thasan, MD, of Thomas Jefferson University Hospital in Philadelphia. “The data do not provide evidence that US is substituting for MRI in large enough numbers to decrease overall MRI volume, although one would hope that at least some substitution is occurring from the cost containment perspective.”

The authors added radiologists don’t want to be forgotten when it comes to MSK US exams. “If radiologists want to maintain their market share as MSK imaging leaders, more emphasis should be placed on increasing their involvement and expertise in MSK US,” they wrote.