“Surgeons should stop carrying out a common type of hip replacement operation on women because of ‘unacceptably high’ failure rates,” The Daily Telegraph newspaper reported today.
The current news is based on a large study that examined data on nearly half a million hip resurfacing operations carried out over a seven-year period in England and Wales.
Hip replacements are common and normally safe and effective. However, one practical drawback is that artificial hips can wear out after 10 to 15 years, requiring further surgery (known as revision surgery). This type of surgery can be more challenging to carry out, so therefore the outcomes can be poorer.
An alternative technique, known as hip resurfacing, has been used in “young-ish adults” aged 55 or younger. This involves removing the damaged surfaces of the bones inside the hip joint and replacing them with a metal surface. This approach is less invasive and leaves the patient with a greater range of movement after surgery. More of the bone is left in the hip joint, so it is believed that the resurfaced joints last longer.
The results of the new study show that hip resurfacing in women resulted in poorer implant survival compared with total hip replacement, irrespective of the size of the implant used. The failure rate of some types of joints was as high as one-in-nine.
In general, hip resurfacing also performed worse in men, except in those with the largest hip bones. Following these findings the researchers recommended that routine resurfacing is not undertaken in women and that the suitability for the procedure is assessed in men before use.
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Where did the story come from?
The study was carried out by researchers from the Universities of Bristol, Plymouth and Exeter and was funded by the National Joint Registry for England and Wales. The study was published in the peer-reviewed medical journal The Lancet.
The news stories were reported appropriately, although the BBC’s headline (“Hip resurfacing prone to failure, say doctors”) could be misinterpreted to mean that the findings apply to all patients, which is not the case. For example, in males with the largest hip bones, hip resurfacing performed just as well as total hip replacement.
What kind of research was this?
This was a cohort study looking at the seven-year survival of differently sized metal-on-metal hip resurfacing in men and women and how they compared with conventional total hip replacements.
This type of study looks at how outcomes differ in people with particular exposures over time. As individuals were not randomly assigned to receive either hip resurfacing or hip replacement (instead their doctors selected the procedure they received), the groups of people receiving the different procedures may differ in ways other than the type of surgery they had.
These other differences may mean that the outcomes described may not only be due to the surgery.
What did the research involve?
The researchers used data from the National Joint Registry for England and Wales, which holds data on hip, knee, ankle, elbow and shoulder joint replacements since 2003, up to seven years after surgery. The analysis was based on 434,560 hip procedures (hip replacements and hip resurfacings) carried out between 2003 and 2011. Of this number, 2,645 of the procedures were bilateral hip replacements, which meant that a person had both hips operated on at the same time.
The researchers looked at the rate of revision, and considered a revision to indicate poor implant survival from the initial surgery. Revision rates were compared for three types of hip procedures:
- metal-on-metal resurfacing
- ceramic-on-ceramic resurfacing (a newer type of hip replacement)
- metal-on-polyethylene replacement (the oldest style of total hip replacement)
They also compared various implant head sizes for the different procedures. The implant head sizes used are determined by the individual person’s anatomy, such as the size of the top of their leg bone that fits in the hip joint, called the femoral head.
The researchers then statistically analysed the results, taking into account patient age, fitness at the time of surgery and implant head size. Separate analyses were conducted for men and women.
What were the basic results?
Of the 434,560 total hip surgeries analysed, 31,932 were hip resurfacings (7.4%). The main results from this study were:
- The percentage of resurfacings that had been revised (further surgery was required) five years after the initial surgery was 8.5% in women (95% confidence interval 7.8 to 9.2) compared with 3.6% in men (95% confidence interval 3.3 to 3.9).
- Hip resurfacing in women resulted in poorer implant survival compared with total hip replacement. This was irrespective of the size of the implant used.
- Hip resurfacing only resulted in similar implant survival rates compared with total hip replacements in men with large femoral heads.
- The size of the implant used was found to be an independent predictor of whether the patient had a revision, with results indicating that smaller head sizes were more likely to be revised than larger ones.
How did the researchers interpret the results?
The researchers concluded that hip resurfacing failure rates are dependent on the size of the femoral head (which influences the size of the implant used) and the patient’s gender. In view of their findings they recommended that “resurfacing is not undertaken in women and that preoperative measurement is used to assess suitability in men”.
The researchers noted that women are more vulnerable to the effects of osteoporosis (weakening of the bones) due to menopausal effects. They speculated that this may offer some explanation as to why revision rates were higher in women.
The results of this large study are of concern, although the authors pointed out that “other considerations need to be taken into account” before dismissing hip resurfacing. For example, they said that resurfacing protects the quality of the femoral bone (by not removing it, as in total hip replacements), which may be an important advantage in the younger patients.
The researchers also noted that not enough is known about how other patient-related outcomes compare between those that receive hip resurfacing and those with total hip replacement.
Significantly, despite the authors’ efforts to adjust their results for confounders, it is always possible that other factors such as pain, activity levels and bone quality influenced the results.
Overall, this study provides some evidence that when looking specifically at failure rates (and need for revision surgery), hip resurfacing may offer no advantage over conventional total hip replacement, with revision rates worse in women than men.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on twitter.