Obese patients may have higher risk of aseptic loosening and osteolysis

Patients who are obese (body mass index [BMI] greater than 30) have a higher rate of postoperative complications after undergoing total hip arthroplasty (THA)—that much is clear from the literature. But the unknowns include the time to presentation for each of the various obesity-related complications after primary THA until revision THA.

During the 2015 annual meeting of the American Assocation of Hip and Knee Surgeons, Ali J. Electricwala, MS, a research fellow at the Stanford Hospital and Clinics, Redwood City, Calif., under the mentorship of Derek F. Amanatullah, MD, PhD, presented research that suggests that increasing BMI adversely affects the mean survival of primary THA. Aseptic loosening and osteolysis requiring revision THA occur significantly earlier in patients who are obese, compared to those who are not.

Data and covariables
Data were based on a retrospective review of 257 patients who underwent revision THA surgery at a single institution between January 2011 and December 2013. Patients were stratified according to age, sex, ASA grade, and preoperative BMI.

Outcome variables included time from primary THA to revision THA and the reason for revision THA. Reasons for revision included aseptic loosening/osteolysis, infection, instability, adverse reaction to metal debris (ARMD), periprosthetic fracture, or miscellaneous.

For the cause of failure, all categorical variables were compared using the Fisher exact test; the Chai Square test was used to compare categorical variables for mean survivorship. After Bonferroni correction, P = 0.001 was considered statistically significant.

Nearly half (124) of the revisions THAs in the database were performed for aseptic loosening/osteolysis. Infection was the second most common reason for revision surgery, followed by instability, ARMD, miscellaneous causes, and periprosthetic fracture. More than a third (92) of the revision THAs were performed for the failure of a primary THA in a patient with obesity.

Early, late revision surgeries
Among all revision surgeries after primary THA, 111 patients (43 percent) underwent revision THAs within 5 years of the index procedure (defined as early). There were 64 mid-term revisions (5 to 10 years after the index procedure) and 82 late revisions (more than 10 years after primary THA).

When researchers looked at the impact of body mass index (BMI) on implant survivorship, they found that an increased BMI was linked to an adverse effect on the mean time to revision THA. Patients with a BMI less than 25 had a 5-year implant survival rates of 75 percent; among the super-obese (BMI greater than 40), it was just 25 percent (Table 1). Similarly, mean survivorship of the primary implant at 15 years was 30 percent for patients with the lowest BMI values and 0 percent for those with the highest BMI values.

The researchers also found a significantly higher rate of early revision THA for aseptic loosening/osteolysis in patients who are obese (P = 0.001). Aseptic loosening was the primary mode of failure in nearly half (41) of the 92 revision surgeries in patients who were obese. Of these revisions, more than half (23) were performed within the first 5 years. This was in stark contract to the 10 revision THAs performed for early aseptic loosening among patient who were not obese.

Thus, this study's findings indicate that obesity is linked to a higher risk of early revision THA due to aseptic loosening/osteolysis. Furthermore, the data indicate that preoperative BMI plays an important role in determining the survivorship of primary implants in THA patients.

Additional coauthors for "Obesity is a Risk Factor for Early Aseptic Loosening and Osteolysis of Hip Replacements" were Rapeepat I. Narkbunnam, MD; James I. Huddleston, MD; William J. Maloney, MD, PhD; and Stuart B. Goodman, MD, PhD. The authors' disclosure information can be accessed at www.aaos.org/disclosure

Jennie McKee is a senior science writer for AAOS Now. She can be reached at mckee@aaos.org

Bottom Line

• This retrospective review of 257 revision THA patients found a significant increase in early revision rates for aseptic loosening/osteolysis in obese THA patients.
• Other reasons for revision included infection, instability, ARMD, periprosthetic fractures, and miscellaneous.
• The researchers concluded that obesity is linked to a higher risk of early revision THA due to aseptic loosening/osteolysis.