Editor’s note: The following content was published in the AAOS Now Special Edition and distributed in June 2020. The content was originally scheduled for the AAOS Now Daily Edition, which publishes each year onsite at the AAOS Annual Meeting but this year’s meeting in March was canceled due to COVID-19. Despite the cancellation, members can access virtual content from the Annual Meeting by visiting the Academy’s Annual Meeting Virtual Experience webpage.

A study based on data from the American Joint Replacement Registry (AJRR), presented as part of the Annual Meeting Virtual Experience by Richard Illgen, MD, of the University of Wisconsin, found significant differences in migration rate and destination in patients treated for periprosthetic fracture (PPF) after total hip arthroplasty (THA), with the highest percentage of patients migrating from small nonacademic centers to large or medium academic centers. A similar pattern was noted for revision THA for other causes, but it did not reach statistical significance.

The investigators reviewed AJRR and linked Centers for Medicare & Medicaid Services (CMS) data to evaluate migration rates and destinations based on hospital size (large, medium, or small) and teaching affiliation (teaching or nonteaching) for all revision THAs (n = 25,980) and revision THAs for PPF (n = 892). All primary and revision THAs for patients 65 years or older as reported to AJRR from Jan. 3, 2012, to Sept. 26, 2018, were included. Cases were linked with CMS data for cases from 2012 to 2017.

Cementless stems were 2.6 times more likely to undergo early revision for PPF than cemented fixations. The overall migration rate was 0.32, and no significant difference was seen by hospital size or teaching affiliation. Migration destination for revision THA differed by hospital size; 19.1 percent migrated to small hospitals, 36.8 percent to medium, and 40.3 percent to large. Regarding teaching affiliation, 66.7 percent of cases migrated to a teaching institution. Migration rates for PPF revisions showed statistical significance comparing small hospitals (0.36) to medium hospitals (0.17, P < 0.001) and nonteaching (0.31) to teaching institutions (0.23, P < 0.01). PPF was the most common cause for early revision THA (less than three months), with a similar rate in all groups (15.6 percent to 18.3 percent).

Overall, the results showed that patterns of migration differed for revision THA based on hospital size and teaching affiliation. Large hospitals and teaching institutions are the preferred destinations for revision THA (Table 1), with demonstrated statistical significance when revision THA for PPF was analyzed (Table 2). PPF was also the most common cause for early revision THA for all hospital sizes and teaching affiliations.

Asked whether any findings were unexpected or surprising, Dr. Illgen told AAOS Now, “Rates of migration after THA complicated by PPF were significant, relatively large, and place a significant burden on affected institutions.”

The authors noted that revision THA represents a significant financial burden for the healthcare system, with the highest costs and complication rates associated with revision THA for PPF. “At present,” they wrote, “the increased cost associated with caring for patients with PPF are not reimbursed adequately by CMS.” They said the volume of primary THAs in the United States continues to rise on an annual basis, with approximately 500,000 procedures per year; it is estimated that the volume of revision THAs will also rise proportionately. Data from 2016 estimated the number of revision THA cases to be between 50,000 and 60,000 cases for that year.

“With national and international registries citing 10 percent to 15 percent of revision THAs being due to PPF, the additional costs associated with treatment can become burdensome for institutions absorbing these cases,” the authors wrote. Previous studies, they noted, have associated cementless femoral fixation with 2.6 times higher risk of early PPF (within 90 days) compared to cemented femoral fixation. “The appropriate use of cemented femoral fixation in at-risk patients for PPF after primary THA could potentially reduce the financial burden, morbidity, and mortality of these complex and challenging postoperative complications,” they wrote.

AJRR: unique data source

Dr. Illgen said he and his colleagues undertook the study because little information had been available regarding migration rates and destinations in THA patients. “The AJRR represents a unique data source to better understand these patterns based on hospital size and teaching affiliation,” he said. “The AJRR provides a unique dataset at the national level, especially when linked to the CMS database, to allow this type of study to be performed. The establishment of the Analytics Institute within the AJRR in February 2019 serves to open the AJRR database to U.S. physician researchers and establishes a straightforward mechanism to utilize this dataset to answer clinically relevant and important questions.”

Dr. Illgen said that further studies are needed to explore other issues related to migration after THA, including state-to-state migration and migration after revision THA. “These follow-up studies are currently being completed utilizing the AJRR and a team of researchers from across the United States,” he said.

Dr. Illgen’s coauthors of Paper 616, “Migration patterns reported in the AJRR for Revision Total Hip Arthroplasty,” are David G. Lewallen, MD; Heena Jaffri; Dena S. Weitzman, OD; and Kevin Bozic, MD, MBA.

Terry Stanton is the senior medical writer for AAOS Now. He can be reached at tstanton@aaos.org.