Total hip arthroplasty (THA) is a reliable treatment for reducing pain and improving function in patients with osteoarthritis of the hip. However, the rate of revision THA procedures being performed is on the rise and is expected to continue to increase, according to Bryan D. Springer, MD, of OrthoCarolina's Hip & Knee Center. "In order to improve long-term THA survivorship, we need to better understand the etiology and risk factors for early failure in primary total hips," he said.

Speaking at The Hip Society/American Association of Hip and Knee Surgeons Specialty Day, Dr. Springer presented the results of a study he and his colleagues conducted to evaluate risk factors for early THA failure, stratified by surgical approach. He noted that complications such as instability, aseptic loosening, cup malpositioning, femoral fracture, and impingement have been associated with various surgical methodologies for THA. "The purpose of our study was to identify whether surgical approach is, in fact, a risk factor for early failure in THA," he said.

Retrospective review
The researchers reviewed data on 6,894 primary THAs performed via either the direct anterior approach (DAA) (n = 2,431) or the posterior approach (PA) (n = 4,463) at a single high-volume tertiary referral hip center between January 2007 and December 2014. The researchers examined incidences of early failure of primary THA, time to failure, and modes of failure in both surgical groups. Early revision was defined as implant failure that necessitated a return to the operating room within 5 years of the index operation.

Primary THAs that were completed at an outside institution, performed after prior hip surgery, or performed via an approach other than DAA or PA were not included in the analysis. Also excluded were primary THAs with recalled implants (ie, metal on metal), conversions from hip hemiarthroplasty, and revision surgeries that resulted from corrosive events.

Instructional Course Lectures, Vol. 63;

"We also excluded cases that were performed within the DAA surgeons' learning curve. The surgeons had to have at least 1 year of experience and needed to have performed more than 50 THA procedures via the DAA approach," Dr. Springer explained. 

Overall, 103 (1.5 percent) of THAs had been revised. The average patient age was 60 years; 60 percent of the patients were male; average body mass index was 29 kg/m2, and average time to failure was 10 months. No statistical differences were found between revision rates when stratified by approach (DAA: 41/2433 [1.69 percent]; PA: 62/4463 [1.39 percent], P = 0.33). Similarly, the time to failure from the index procedure as well as all other demographics between the groups were not statistically different, noted Dr. Springer.

Failure mechanisms
The researchers did find differences in femoral loosening, instability, and other risk factors for failure between the DAA and PA groups. For example, the rate of femoral loosening was statistically higher in the DAA group compared to the PA group (0.62 percent and 0.11 percent, respectively, P = 0.0006).

"In addition, the overwhelming majority—75 percent—of all revisions performed for femoral component loosening were done through the DAA. And among the 41 DAA hips that were revised, the majority were revised for femoral loosening, which was also statistically significant," said Dr. Springer.

Revisions for other etiologies such as cup malposition and psoas tendon irritation were also statistically higher in the DAA group. However, the overall rate of revision for instability was higher in the PA group (0.45 percent) than in the DAA group (0.25 percent). "Interestingly, we found no differences between the groups in infection, incidences of periprosthetic fracture out to 5 years, and acetabular loosening," said Dr. Springer.

He added, "Our numbers weren't high enough to get a good statistical analysis on the stem types that were used. We did find, however, that the tapered wedge stem—particularly the tapered wedge stems in Dorr A-type bone—appeared to have higher failure rates for femoral loosening."

He concluded that, at a high-volume center, the overall incidence of early failures in THAs is low for both DAA and PA. "But keep in mind that no approach is a panacea and each approach can be associated with its own unique risk factors for failure," he said. 

Maureen Leahy is assistant managing editor of AAOS Now. She can be reached at leahy@aaos.org

Bottom Line

• Researchers examined incidences of early failure of the index procedure, time to failure, and modes of failure for DAA and PA THAs.
• Both approaches had low incidences of early failure.
• DAA was associated with higher rates of failure for femoral loosening, cup malposition, and psoas tendon irritation.
• PA was associated with higher rates of failure for instability.