Perspective

Study: MRI predicts failure in MoM hips by identifying tissue damage

Researchers from Hospital for Special Surgery have found a way to identify synovitis using MRI in patients who underwent metal-on-metal hip resurfacing arthroplasty before symptoms appear.

“The study shows that synovitis exists in asymptomatic people in a fairly high prevalence,” Hollis G. Potter, MD, chief of the Division of Magnetic Resonance Imaging at Hospital for Special Surgery, stated in a press release. “If that is the case, symptoms alone are insufficient to determine the health of an implant. You can’t wait for people to be sore before we evaluate them for this potential problem.”

 

Hollis G. Potter

Potter and colleagues evaluated 69 consecutive patients (74 hips) who were referred to Hospital for Special Surgery from three different institutions after a metal resurfacing arthroplasty, according to the abstract. Two radiologists evaluated the MRIs of patients were divided into two groups based on whether they were asymptomatic with unexplained pain or symptomatic with mechanical problems. Both radiologists were blinded to which groups patients belonged to.

In asymptomatic hips, Potter and colleagues found 68% of cases showed an average volume of synovitis of 5 cm³. In 75% hips with mechanical problems, the researchers found an average of 10.3 cm³, while 78% of hips with unexplained pain had an average volume of synovitis of 31 cm³, according to the abstract.

Additionally, there were no significant differences between serum ion levels or in X-rays in either group.

“Many people focus on serum ion levels,” Potter said. “I think the direction of the pendulum is changing now, away from serum ion levels and toward imaging, or at least not to focus so much on serum ion levels to predict potential damage. Cross-sectional imaging is the way to go, and specifically, MRI over CT based on its superior soft tissue contrast.”

Reference:

Nawabi DH. J Bone Joint Surg Am. 2013;doi:10.2106/JBJS.K.01476.

Disclosure: Potter received research support from General Electric Health Care for this study.

Researchers from Hospital for Special Surgery have found a way to identify synovitis using MRI in patients who underwent metal-on-metal hip resurfacing arthroplasty before symptoms appear.

“The study shows that synovitis exists in asymptomatic people in a fairly high prevalence,” Hollis G. Potter, MD, chief of the Division of Magnetic Resonance Imaging at Hospital for Special Surgery, stated in a press release. “If that is the case, symptoms alone are insufficient to determine the health of an implant. You can’t wait for people to be sore before we evaluate them for this potential problem.”

 

Hollis G. Potter

Potter and colleagues evaluated 69 consecutive patients (74 hips) who were referred to Hospital for Special Surgery from three different institutions after a metal resurfacing arthroplasty, according to the abstract. Two radiologists evaluated the MRIs of patients were divided into two groups based on whether they were asymptomatic with unexplained pain or symptomatic with mechanical problems. Both radiologists were blinded to which groups patients belonged to.

In asymptomatic hips, Potter and colleagues found 68% of cases showed an average volume of synovitis of 5 cm³. In 75% hips with mechanical problems, the researchers found an average of 10.3 cm³, while 78% of hips with unexplained pain had an average volume of synovitis of 31 cm³, according to the abstract.

Additionally, there were no significant differences between serum ion levels or in X-rays in either group.

“Many people focus on serum ion levels,” Potter said. “I think the direction of the pendulum is changing now, away from serum ion levels and toward imaging, or at least not to focus so much on serum ion levels to predict potential damage. Cross-sectional imaging is the way to go, and specifically, MRI over CT based on its superior soft tissue contrast.”

Reference:

Nawabi DH. J Bone Joint Surg Am. 2013;doi:10.2106/JBJS.K.01476.

Disclosure: Potter received research support from General Electric Health Care for this study.

    Perspective
    Lawrence D. Dorr

    Lawrence D. Dorr

    Once in a while, amongst the thousands of annual orthopedic publications, an article opens the door to answers to a problem that has confounded us surgeons. Unexplained pain with hip replacement is such a problem. This study is of hip resurfacing, but the methodology described to diagnose excessive synovitis has huge potential for use in joints with unexplained pain. Hollis Potter, MD, has once again waved her imaging wand to create a diagnostic tool which hopefully she will extend to conventional total hip replacement, total knee replacement and polyethylene articulations.

    Like many of the most important orthopedic discoveries, this study provides a valuable clinical tool without detailing the basic science behind it. The large head metal-on-metal articulations failed because of poor engineering by the companies, but the consequences have fallen on us as surgeons. Our patients have the complications and this study helps us help them. Perhaps synovitis is multifactorial. Science needs to answer why patients with smaller implants and women suffer more. Is genetics a factor? Is component position most important? Why did patients not experience these complications of synovitis, pseudotumors and high ions with 28-mm metal-on-metal hip replacements? We can await these definitive scientific answers while we expand this valuable clinical diagnostic method for unexplained hip pain.

    • Lawrence D. Dorr, MD
    • Professor of Orthopedics University of Southern California Los Angeles

    Disclosures: Dorr is a stock owner for Total Joint Orthopedics and receives royalties from Don Joy Orthopedics.