There is a direct link between the number of total knee replacement surgeries and obesity, according to a study published online ahead of print June 4 in the Journal of Bone and Joint Surgery. Lead study author Peter B. Derman, MD, MBA, an orthopedic surgery resident at the Hospital for Special Surgery in New York, and colleagues reported that the number of total knee replacement surgeries more than tripled between 1993 and 2009, while the number of total hip replacements doubled in the same time period.
“We observed that growth of knee replacement volumes was far outpacing that of hip replacements and were curious as to the origins of this trend,” said Dr. Derman. He and his research colleagues found that an increase in the prevalence of overweight and obesity in the US accounted for 95% of the higher demand for knee replacements, with younger patients affected to a greater degree.
The researchers compiled longitudinal data on total hip arthroplasty and total knee arthroplasty volume, length of hospital stay, and in-hospital mortality from the Nationwide Inpatient Sample. They then calculated reimbursement using information available in the Federal Register and Centers for Medicare and Medicaid databases. Trends in body mass index (BMI) were determined from Behavioral Risk Factor Surveillance System findings and the size of the surgical workforce was based on membership data from the American Academy of Orthopaedic Surgeons.
Among the study’s findings:
• Growth in total knee arthroplasty volume far outpaced that of total hip arthroplasty among those patients with a BMI of 25 kg/m2 or above, but not for those with a BMI of less than 25 kg/m2.
• In 1993, surgeons performed 1.16 total knee replacements for every total hip replacement, but this ratio grew to 1.60 by the year 2009.
• Patients ages 18 to 64 years experienced a more rapid rise in obesity, compared to patients older than 65 years.
• From 1997 to 2009, the share of patient’s ages 18 to 64 years undergoing total knee replacement rose 56% compared to 35% for total hip replacement.
• Surgeon per-case reimbursement for total knee replacement fell from approximately $3000 in 1995 to $1560 in 2009. Surgeon fees for total hip replacement dropped from $2840 to $1460 in the same time period.
• As the data represent an approximate 48% drop in fees for both procedures, surgeons do not appear to be performing more total knee replacements over total hip replacements due to higher reimbursement.
• Hospital reimbursement, length of hospital stay, and in-hospital mortality pertaining to total knee replacement and total hip replacement also declined between 1995 and 2009.
Commenting on the study findings, Dr. Derman said, “Because excess body weight appears to be more damaging to the knee than to the hip, the increasing prevalence of overweight and obesity may explain the growing demand for knee replacements over hip replacements. If rates of overweight and obesity continue to climb, we should expect further acceleration in the number of knee replacements performed annually in the United States with a more modest increase in hip replacement volumes.”