A new study of 35,000 US patients, one of the largest of its kind, suggests while the risk of total hip implant failure is low, it is slightly higher in women than in men. It has prompted calls for studies to investigate which types of implants are more likely to succeed in women than men.

Maria C.S. Inacio, of the Southern California Permanente Medical Group, San Diego, and colleagues write about their findings in the 18 February online first issue of JAMA Internal Medicine.

They show of patients undergoing total hip replacement, women were 29% more likely to need repeat surgery within the first three years than men.

This figure was independent of other factors such as risk factors already present in the patient, the surgeon who performed the procedure, or the hospital.

Every year, around 400,000 Americans undergo total or partial hip replacement to regain lost mobility and ease the pain caused by injury or arthritis.

In the background section of their study, Inacio and colleagues note that total hip arthroplasty (THA), more commonly known as total hip replacement, is performed more often in women than in men.

Researchers have studied sex-specific risk factors in other major surgical procedures, and it is important to do the same for THA, because of the anatomical differences between men and women, say the authors.

For their study, they looked at data on 35,140 THA procedures performed at 46 hospitals. The patients, whose average age was nearly 66, and of whom 57.5% were women, had been followed for a median of three years, and had been enrolled in a total joint replacement registry between 2001 and 2010.

When they analyzed the data they found, "at the median follow-up of 3.0 years women have a higher risk of all-cause (HR [hazard ratio], 1.29) and aseptic (HR, 1.32) revision but not septic revision (HR, 1.17)".

Overall, 97.4% of implants survived to the five year follow-up mark but there was a significant difference between men and women.

Hip implant failure is rare, but when it does fail, the problem is usually infection (septis), or other non-infection (asepsis) reason such as broken bones, instability, or the joint has worked itself loose and dislocates.

After adjusting for potential influencers, the researchers found that women were more 29% more likely to need revision surgery due to all causes, 32% more likely for aseptic revision and 17% more likely for septic revision.

When they looked at the types of procedure, the researchers found that a higher proportion of women than men received the smaller, 28 mm femoral heads (28.2% versus 13.1%).

And a higher proportion of women (60.6%) received metal on highly cross-linked polyethylene-bearing surfaces than men (53.7%).

A higher proportion of men received 36 mm or larger femoral heads (55.4% vs 32.8%), and metal on metal-bearing surfaces (19.4% percent vs 9.6%).

The authors conclude that sex differences play a role in implant failure after total hip arthroplasty (THA), and this could be important for designing new types of hip replacements and helping make the right choice for patients.

In an accompanying commentary, Diana Zuckerman, of the National Research Center for Women & Families, Washington, DC, says it is important for orthopedics to have this kind of research because men and women's bodies are different.

She describes the study as an "important first step" in understanding these differences for THA revision rates.

However, she notes that the "the relatively small number of revisions and large number of potentially confounding variables in these short-term data make it challenging to use these data to help reduce the likelihood of revision surgery".

"Longer follow-up is necessary for hip implants," she notes, suggesting that:

"What is urgently needed is long-term comparative effectiveness research based on larger sample sizes, indicating which THA devices are less likely to fail in women and in men, with subgroup analyses based on age and other key patient traits, as well as key surgeon and hospital factors."

"Such data would enable patients and their physicians to choose the hip devices and surgical techniques that are most likely to be successful for a longer period," she adds.

Funds from the Center for Devices and Radiological Health at the US Food and Drug Administration helped finance the study.

Earlier this month, researchers writing in the online issue of JAMA Internal Medicine described how they used "secret shopper" techniques to uncover huge variations in the price of hip replacements in hospitals across the US..

Written by Catharine Paddock PhD