CORR Insights^®: Are Females at Greater Risk for Revision Surgery After Hip Resurfacing Arthroplasty With the Articular Surface Replacement Prosthesis?

Where Are We Now?

There is conflicting evidence regarding whether the risk of complications differs by gender after metal-on-metal (MoM) hip resurfacing arthroplasty [2]. MoM hip resurfacing arthroplasty decreases volumetric wear, increases stability due to larger femoral head sizes, and better preserves bone stock on the femoral side when compared to conventional THA with metal-on-polyethylene bearings. However, MoM hip resurfacing arthroplasties are prone to adverse local tissue reaction (ALTR), pseudotumour formation, osteolysis, and high metal ion levels.

Large national arthroplasty registries [4, 5] have identified a number of risk factors for early revision following MoM hip resurfacing including smaller femoral head sizes, developmental dysplasia of the hip, certain implant designs, and older patient age. Additionally, those analyses revealed that women were at a greater risk for revision than men when managed with primary resurfacing hip replacements compared to the results of primary conventional THA [4, 5]. Women who received the Articular Surface System ([ASR], DePuy, Warsaw, IN, USA) had worse patient-reported outcome measures and demonstrated higher blood metal ion levels than men. After controlling for other confounding variables, women were at greater risk for revision surgery than men, but sex was not an independent risk factor for ALTR [4, 5]. Another study [3] found considerable differences in the percentages of failure between brands and component sizes following hip resurfacing arthroplasty. The study also found that women were at a greater risk of revision than men.

Where Do We Need To Go?

Orthopaedic research rarely reports on complications stratified by gender. Could it be that orthopaedic surgery has had a blind spot for female hips? If higher blood metal ion levels can be found in female patients who underwent hip resurfacing arthroplasty, could this also be the case in conventional THA with MoM bearings?

Also, I wonder whether the data and the conclusion in the current study are influenced by a selection bias given the unusually small percentage of women (27% in cohort A and 31% in cohort B) operated with the ASR implant? In the particular case of the ASR implant, indications for revision could have been influenced by the recall of the product. When a product is recalled, it is possible that a patient’s willingness to undergo revision is increased because of anxiety about the potential harms that a device could cause. Although I do not believe that patient demand is a sufficient reason for revision, my observation is that it does sometimes drive surgical decision-making in practice. If anxiety levels differ between men and women, and patient demand may drive the usage of revision surgery, it seems possible that the conclusion of the analysis—that women are at greater risk for revision—could be influenced by this issue. It should be noted, however, that the authors of a recent study [6] concluded that the ASR product recall did not affect the threshold for revision of MoM hip replacement, and that Donahue and colleagues explored anxiety as a predictor. They did not find it to be associated with revision surgery, but it still seems an issue worth keeping in mind.

Most studies investigating risk factors for early revision of MoM hip resurfacing arthroplasty rely on registry data. Registries are valuable tools for monitoring orthopaedic implants, but are less appropriate for studying serum ion levels. Given the enormous sensitivity of analysis methods for serum metal levels like atomic absorption spectrometry, reliable results can only be obtained by identifying the patients without any additional metal implants besides the artificial hip. This task becomes more difficult over time [1].

If it is true that serum metal levels are higher in female patients, we need to scrutinize not only female patients with a hip resurfacing arthroplasty, but all those with a MoM hip.

How Do We Get There?

There are several centers dedicated to the research of serum metal ion levels of patients with THA in continental Europe, England, and the United States. However, there is not enough time to design, conduct, and evaluate prospective randomized clinical trials to determine whether female patients develop higher serum ion levels. As an alternative approach, we could have large national registries pool the data of former prospective studies. We could then reevaluate the living patients in a clinical setting and stratify by gender.

It is striking that women had a greater risk for revisions than men, but not an independent risk factor for ALTR. This can only be evaluated by seeing the patients clinically. At a minimum, one of the large centers could perform such an investigation alone. There are numerous reasons for elevated serum metal levels such as implant impingement, errors of head size, and material to only name a few. Those factors can best be detected by reviewing the surgical reports and radiographs of the respective patients. We need to know whether women with MoM hips are at risk for premature failure.