CORR Insights®: MRI of THA Correlates With Implant Wear and Tissue Reactions: A Cross-sectional Study

Where Are We Now?

Evaluating patients with a problematic hip arthroplasty involves taking a careful history, performing a thorough physical exam, and interpreting the patient’s plain radiographs. Additional laboratory tests aid in diagnosing infection. Together, these elements of a traditional work-up provide the data needed to evaluate and diagnose most patients with painful THAs. In some circumstances, however, the diagnosis remains elusive.

Recent improvements in MRI technology have allowed us to evaluate the periarticular soft tissues about a THA [1]. Indeed, MRI has proven useful to diagnose, and evaluate the severity of adverse local tissue reactions to metal ions that arise from implant wear or corrosion [3]. In their excellent paper, Koff and colleagues [2] demonstrate that MRI can do more than just evaluate for solid masses and fluid collections in the periarticular tissue; MRI can differentiate the soft-tissue reactions that are characteristically found about certain bearing materials. This observation, which is nicely corroborated with histology and intraoperative findings, demonstrates the expanding role that MRI may have in the future for detailed evaluation of periprosthetic soft tissues, and potentially for monitoring of new implants and bearing surfaces.

Where Do We Need To Go?

The study by Koff and colleagues [2] is important as it establishes the capabilities of the MRI technique in evaluating periarticular soft tissues. It is suggested in this article that the MRI may help to differentiate bearing couples that have durable long-lasting results from bearing couples that may be associated with an adverse reaction, such as metal associated adverse local tissue reaction or osteolysis from conventional polyethylene. As a proof of concept, I think it would be informative to investigate whether this novel MRI technique can differentiate the soft-tissue reaction associated with conventional polyethylene from the soft-tissue reaction (or perhaps lack thereof) associated with highly crosslinked polyethylene. Is there a characteristic MRI appearance of the tissues adjacent to a durable and long-lasting bearing couple?

It is also interesting to think about how this technology can potentially help us with the challenging problems we face today in hip arthroplasty. Can MRI help us diagnose chronic periprosthetic infection? It is easy to imagine that the periarticular soft tissues in a chronically infected joint may have a characteristic MRI appearance. Further, can MRI help us to diagnose the cause of recurrent hip instability when the implants appear to be well positioned? Again, one can imagine that hip abductor atrophy, disrupted posterior capsule, torn gluteus medius and minimus tendon insertions, or perhaps even characteristic bone bruise patterns in areas of bone-to-bone impingement could provide information regarding why a patient continues to dislocate. Such findings may even suggest surgical treatment strategies.

How Do We Get There?

Now that the capabilities of the MRI technique are more firmly established, investigators should compare the MRI appearance of periarticular tissues in patients with conventional and highly crosslinked polyethylene. This may identify the MRI appearance of a hip replacement with a durable bearing couple. Similarly, I would urge investigators to compare the MRI appearance of periarticular tissues in patients having reoperation for infection to the MRI appearance in patients having surgery for other reasons. Can a blinded observer identify the infected cases based only on MRI appearance? Finally, investigators should compare preoperative MRI findings with intraoperative findings in patients undergoing reoperation for recurrent dislocations. Do findings of abductor atrophy, abductor tendon tears, disrupted posterior capsule, or bone bruises correlate with intraoperative findings for the cause of recurrent instability?

For all of these potential studies, pioneers in periarticular MRI must collaborate with orthopaedic surgeons. Together, they can identify the most clinically important problems, and then perform well-designed and careful investigations to address those problems. As technology advances well beyond the expertise of orthopaedic surgeons alone, healthy multidisciplinary collaboration such as was demonstrated in this study will continue to advance orthopaedic science and benefit patient care.