Wear is not primary reason for THA failure

Despite continued improvements in surgical technique and implant devices, revisions to total hip arthroplasty (THA) procedures in the United States have not decreased. In fact, as the patient population has expanded to include younger, more active individuals along with growing numbers of “baby boomers,” revisions are expected to significantly increase over the next several decades, according to Kevin J. Bozic, MD, MBA.

“Understanding the cause of failure and type of revisions is essential in guiding research, implant design, clinical decision making, and healthcare policy related to THA,” he said. “It is also essential to improving long-term patient outcomes.”

At the 2009 Annual Meeting, Dr. Bozic reported on a large, retrospective study of THA revisions, using the newly adopted diagnosis and procedure codes to analyze clinical, demographic, and economic data from more than 51,000 revision THA procedures.

NIS database casts wide net
THA revision procedures were selected from the Nationwide Inpatient Sample (NIS) based on ICD-9-CM diagnosis and procedure codes adopted in 2005 for failed total joint replacements and revision total joint arthroplasty procedures (Table 1). All procedures were performed in the United States from October 1, 2005, to December 31, 2006.

“In 2006, the NIS had a sample size of approximately 8 million records from 1,045 hospitals in 38 states, which represented about 20 percent of all discharges from community hospitals in the United States, regardless of payment source,” reported Dr. Bozic. “The large size of the database means the NIS is particularly well suited for epidemiologic studies related to specific procedures or diseases in the national population.”

Most common reasons for revision
Dr. Bozic and his colleagues found instability/dislocation to be the most common reason for THA revision, followed by mechanical loosening and infection. Previous data suggested aseptic loosening, bearing surface wear, and osteolysis as the primary causes of THA failure. Additional findings include the following:

• The most common cause for acetabular revision and isolated head and liner exchange was also instability/dislocation.
• Mechanical loosening was the primary reason for all component revision along with isolated femoral component revision.
• Infection was the primary reason for a very high percentage of arthrotomy and removal of prosthesis procedures.

Sharp regional differences
The analysis found regional differences in cost, hospital stays, and number of procedures. The average billed charges for all types of revision THA procedures were $54,553. The highest average total charges were in the West ($67,779) and the lowest in the Midwest ($47,504).

The Midwest also had the shortest average hospital stay at 5.6 days; the Northeast had the longest at 6.8 days.

The South leads the country in revision THA procedures with 36.7 percent of all procedures; reporting the lowest volume was the North­east with 17.0 percent (Table 2).

Call for coding action
“Despite numerous case series in the literature documenting lower dislocation rates with enhanced soft-tissue repair techniques and the use of large diameter femoral heads, hip instability/dislocation was the primary indication reported for a large percentage (22.5 percent) of revision THA,” said Dr. Bozic.

“These findings represent important information for orthopaedic surgeons, device manufacturers, and THA patients, and suggest additional research is necessary to understand the current causes of THA instability,” Dr. Bozic continued.

Dr. Bozic also suggested that certain head and liner exchange procedures are being incorrectly coded as component revisions—artificially inflating the prevalence of all component revision procedures.

“As additional experience is gained with the new ICD-9-CM diagnosis and procedure codes related to revision to THA, valuable insights will be gained into THA failure mechanisms, which may help guide future research implant design, clinical decision making, and healthcare policy related to total hip arthroplasty,” he concluded.

Co-authors for “The Epidemiology of Revision Total Hip Arthroplasty in the United States” include Steven M. Kurtz, PhD; Edmund Lau, MD; Kevin Ong, PhD; Thomas P. Vail, MD, and Daniel J. Berry, MD.

The authors report no conflicts of interest with this study.

Annie Hayashi is the senior science writer for AAOS Now. She can be reached at hayashi@aaos.org