Hollis Potter, MD, Chairman of the Department of Radiology and Imaging at HSS, has spent more than 20 years working to refine a technique that most experts once thought impossible, maybe even unsafe: examining metal joint replacements in the body using MRI.
Propelling her and her HSS colleagues forward was a belief that MRI would provide distinct advantages over other imaging modalities used to help diagnose complications after arthroplasty. These complications include inflammatory synovitis, caused when plastic or metal debris from an implant wears off, tears in the surrounding tendons and loosening of the implant where it attaches to the bone. Although HSS has very low infection rates after implant surgery, those can occur as well.
Today, Dr. Potter and colleagues have published numerous studies showing that not only is MRI safe for total joint imaging, it’s also very efficacious. "An X-ray doesn’t show the soft tissue, only the alignment of the implant related to the bone," Dr. Potter explains. "Bone scanning is sensitive, but it’s not specific. It can show us signs of abnormal bone turnover but can’t explain why it’s happening. We’ve demonstrated that MRI is far and away the most accurate, noninvasive means by which to assess for adverse tissue reactions to the implants."
Orthopaedic surgeon Eduardo Salvati, MD, credits Dr. Potter with helping to advance the understanding of thromboembolism after total hip replacement. "We have learned that clots can on occasion extend to the proximal iliac veins and vena cava," he says. "Likewise we determined the efficacy of pneumatic compression and intraoperative heparin in preventing clots and the adverse effect of prosthetic wear debris to the periprosthetic tissues."
There is a learning curve to the interpretation of MRI following joint replacement, says Dr. Potter, and HSS is fortunate to have radiologists who subspecialize in this area. They collaborate closely with surgeons and pathologists to identify the precise cause of the pain and help develop a means by which to address it. That may entail surgical revision of the implant or repair of the surrounding tissues. In other cases, complications can be addressed with physical therapy and other less-invasive treatments.
"There’s a huge demand for this technology, not only from HSS surgeons but from outside surgeons who refer patients experiencing pain related to complications after surgery," Dr. Potter says. "It’s so fulfilling to be able to figure out what’s going on and to help come up with a treatment plan."
MRI has also emerged as an important study tool for learning how to improve implants. Analysis of the wear from a retrieved implant correlates to findings from the prerevision MRI, suggesting new ways to predict which implants are likely to fail and potentially make corrections. Another promising area of research concerns periprosthetic joint infections, says Dr. Potter. "We’re applying different pulse sequences that we believe will be more sensitive to joint infections, in turn helping us make a more accurate diagnosis."
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