Arthritis Today

Success With Total Hip Replacements Is All About the Numbers

Surgeons who perform more hip surgeries per year have fewer complications.


For restoring function and reducing pain, total hip replacement surgery is one of the most successful, cost-effective and safest options available – yet surgery-related complications do occur. A new study published recently in the journal BMJ has found that patients whose surgeons perform more than 35 total hip replacements (THR) per year – roughly three or more per month – have fewer complications compared to patients whose surgeons don’t meet that threshold.

Researchers at the University of Toronto in Canada analyzed the administrative health records of 37,881 people with osteoarthritis from the province of Ontario who got their first THR between 2002 and 2009. They pulled data on the rates of complications – including venous thromboembolism (blood clots) or death within 90 days of the surgery, as well as infection, dislocation or revision within two years of the surgery. They also gathered information on patient characteristics, such as age, socioeconomic status, additional health conditions and frailty.

The researchers then matched the patients – both those with and without complications – to their surgeons, and looked at the annual number of total hip replacements performed by those surgeons.

They calculated that patients whose surgeons had performed more than 35 THR in the preceding year had a 30 percent lower rate of early dislocations or revisions compared to patients whose surgeons had performed 35 or fewer procedures in the prior year. Patients operated on by these “high volume” surgeons also had lower risks of dislocation and of needing a revision than those with “low volume” surgeons.

Even for surgeons under the 35-a-year threshold, the risk of complications continued to rise as surgery volume fell. In other words, surgeons doing 25 surgeries a year, for example, had fewer complications than those performing only 10 a year.

The idea that higher volume leads to better outcomes isn’t limited to surgeons. Previous studies have found that complication rates after total joint replacement can vary widely by hospital, but generally are lower in hospitals with a higher volume of surgeries. One study – published in Arthritis & Rheumatism in August 2011 – found that when it come to total hip replacements, hospitals that do more than 200 surgeries a year have significantly fewer complications than those with lower volume.

“It’s well-established that increased volumes are generally correlated with improved outcomes following surgery, and it makes sense that if you do more of something, you will probably get better at it,” explains the lead researcher of the current study, Bheeshma Ravi, MD, PhD, a resident physician at the University of Toronto. “It’s also likely that surgeons are more apt to perform procedures they feel comfortable performing, and this might be reflected in the volume of their practice.”

In an accompanying editorial in BMJ, Karl Michaëlsson, a professor of medical epidemiology and senior consultant in orthopaedic surgery at Uppsala University, in Sweden, says these findings suggest “one dislocation or revision would be prevented in every 100 or so patients if they switched from a low volume to high volume surgeon.”

Although higher risks of complications were seen with low surgeon volume, a surgeon’s overall experience (measured in years of practice) did not appear to be a factor. “We were surprised, but it was interesting to see that experience was not necessarily the driver of lower complications,” Dr. Ravi explains. “It really suggests that it is the act of performing the surgery over and over again, and doing so in the recent past.”

This data is a little easier to come by in Canada, where there is a universal system of healthcare and provincial administrative databases. But Dr. Ravi says this kind of information is accessible in other regions in North America and Europe, and he believes there’s a value in other centers using the method employed in this study to determine the level of surgeon volume at which the complication rate declines.

“The number 35 in our study is just something that came out of the data,” Dr. Ravi explains. “What I would love to see is people using the technique for their area and health care providers, trying to actually pinpoint what the specific threshold or cutoff for volume is in their region.”

The finance website NerdWallet – which “hire[s] nerds to analyze complex decisions” – did something similar recently in the U.S., after the Centers for Medicare & Medicaid Services released large amounts of physician data to the public in early April. NerdWallet crunched the numbers on more than 3,400 orthopaedic surgeons and came up with 50 as the number of hip surgeries a surgeon should perform per year to be considered “high volume.”

Dr. Michaëlsson says the methods used to determine the surgeon volume threshold in the Canadian study are certainly more precise than methods used previously, but he thinks more research still is needed on this topic. “My view is that recommendations should not be based on a single study. We have to repeat this study design in other settings and we will see if can end up with a similar surgeon volume,” he explains.

But Dr. Ravi says for now, he believes his findings suggest patients should feel comfortable asking about an individual surgeon’s track record instead of simply looking at how many procedures are done annually at a particular hospital.

“Patients should feel empowered to ask how many procedures surgeons have done in the last year and see if those numbers are reassuring to them. You don’t necessarily need someone who does 200 or 300 a year, but our study suggests that it might be less than ideal to go to someone who only does a few a year,” he says.