Study Reports Large Increase in Hip Prosthesis Dislocations in Past Two Decades

Editor’s note: The following 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 at aaos.org/VirtualAAOS2020.

A study that was presented as part of the Annual Meeting Virtual Experience reported that the annual volume of prosthetic hip dislocations presenting to U.S. EDs more than tripled between 2000 and 2018. “One plausible explanation for the observed trend is that the number of patients who underwent total hip arthroplasty (THA) increased over the study period,” said Kevin Pirruccio, BA, who presented the findings, as the incidence of prosthetic hip dislocation has not changed appreciably.

Mr. Pirruccio, a medical student at the University of Pennsylvania, told AAOS Now that he and his colleagues undertook the study upon noticing that although prosthetic hip dislocation rates reported in the literature were well characterized up to one or two years after the index procedure, “dislocation rates after these dates varied widely, with little data available pertaining to the entire U.S. population undergoing primary THA.”

The epidemiological study identified cases of prosthetic hip dislocations in the National Electronic Injury Surveillance System (NEISS) database—a nationally representative probability sample of about 100 designated hospital EDs stratified by both hospital size and geographic location, from which weighted national estimates and sampling errors for queried injuries may be derived. It is operated by the U.S. Consumer Product Safety Commission, which has maintained this statistically validated injury surveillance and follow-back system for nearly 50 years.*

Each yearly sample in the NEISS database was queried between 2000 and 2018 for all injuries classified as dislocations of the hip in individuals aged 18 to 99 years. In total, 1,757 unique cases of prosthetic hip implant dislocations were identified, yielding 72,760 national weighted estimates.

Mr. Pirruccio said the investigation yielded three major findings. First, the number of patients presenting to U.S. EDs with prosthetic hip dislocations more than tripled during the study period, from about 2,500 in 2000 to more than 8,000 in 2018. However, he said, the second finding was that “when compared to the total number of patients predicted to be living in the United States with a prosthetic hip implant, the rate of dislocation has not significantly changed over time.” Third, “applying forward a linear regression model based on these historical trends predicts that by the year 2035, there will be more than 11,000 patients presenting to U.S. EDs with prosthetic hip dislocations each year.”

He commented, “It was surprising to learn that despite myriad advancements in surgical technique and implant design that have certainly lowered individual short-term rates of prosthetic hip dislocations in the United States, the rising number of dislocations simply seems to be an inevitable consequence of the increasing annual volume of THA procedures performed each year. It is imperative to identify techniques that will minimize this burden.” In the authors’ full-length manuscript, they discussed several options that may decrease future dislocation incidences, including but not limited to:

• prosthetics with larger femoral head diameters
• implementation of dual-mobility cups
• usage of radiologic templating to prevent limb length discrepancies

Economic burden

The study authors wrote that their model highlights the potential economic burden of prosthetic hip dislocations in the United States as the prevalence of THA continues to rise. Prosthetic hip dislocations, they wrote, remain among the costliest such complications and may be a factor in the closure of a financially distressed hospital.

Mr. Pirruccio noted that although “the vast majority of patients with prosthetic hip dislocations will be discharged from the ED after successful closed reduction of the hip,” the median hospital charge for the entire length of stay associated with a prosthetic hip dislocation presenting to a U.S. ED and requiring hospital admission was $35,845 in 2014. “Therefore, if about 40 percent of the 11,000 projected prosthetic hip dislocations in 2035 require hospital admission from the ED, total hospital charges could surpass $100 million.”

“In order to ensure that this burden does not become unsustainable for EDs and the national healthcare system as a whole, orthopaedic surgeons will likely need to adopt multimodal approaches for minimizing long-term instability,” Mr. Pirruccio commented. “This may not only include further advances in surgical technique, prosthesis design, and preventative strategies, but also the widespread implementation of predictive tools capable of identifying patients most at risk for dislocation.”

The study is limited by its use of a retrospective survey, presenting the possibility for reporter bias within entries, which could lead to patients accidentally being excluded from analysis. Similarly, he said, “We were unable to collect variables related to the index procedure from patients, including dates of surgery or types of implants used.”

He noted that the study’s retrospective analysis relied on the use of a nationally representative, weighted survey sample of U.S. EDs and therefore did not provide several clinically relevant patient health and outcome variables that would tell a more comprehensive story regarding how patients were treated and their overall recovery. “We hope that future studies may use institutional-level data to answer these remaining questions, especially for patients experiencing a dislocation more than two years after an index procedure.”

*Frequently asked questions pertaining to data collection can be found at https://bit.ly/2LJrlF9.

Mr. Pirruccio’s coauthors of “The Burden of Prosthetic Hip Dislocations in the United States is Projected to Significantly Increase by 2025” are Ajay Premkumar, MD, MPH; and Neil P. Sheth, MD.

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

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