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One More Reason to Take That Weight Off!

Study Finds Obesity Limits Range of Motion, Causes Longer Recovery after Knee Surgery

SAN FRANCISCO—March 5, 2008

Obesity limits a patient's range of motion (ROM), prolongs recovery and extends the need for physical therapy after total knee replacement surgery, according to a study presented today by Geoffrey Westrich, MD, of Hospital for Special Surgery at the 75th Annual Meeting of the American Academy of Orthopaedic Surgeons.

The study found that a patient's body mass index (BMI) had a direct correlation on the knee's ROM and the need for manipulation under anesthesia. Body mass index (BMI) is a measure of body fat based on height and weight that applies to both adult men and women.  While fewer than 10 percent of patients with a BMI of less than 25 required manipulation in physical therapy to achieve greater flexibility and break up scar tissue, almost 20 percent of patients with a BMI of 25-30 required manipulation.

According to the National Institutes of Health, people with a BMI of 25 - 29.9 are considered overweight and a BMI of 30 or greater would indicate obesity.

"For anyone considering knee replacement surgery, recovery time is an important consideration. Patients ask 'Is my pain going to be relieved? Will I have better range of motion?'" said Dr. Westrich, lead author and associate professor of orthopedic surgery at Hospital for Special Surgery in New York City. "Our findings will help set more realistic expectations for overweight patients. They need to be counseled that their weight will likely impede their recovery."

The study compared data from 309 patients (400 knee replacements) who underwent total knee replacement surgery at Hospital for Special Surgery. Researchers evaluated the affect of BMI on ROM and the need for manipulation under anesthesia. Patients were divided into groups according to their BMI, from less than 25 to greater than 29.9.

Other significant findings in the study include:

  • The greater a patient's BMI, the less ROM they can expect after knee surgery;
  • Age was not a predictor for ROM;
  • Gender is a predictor for ROM and need for manipulation. Regardless of BMI, men had a 4.6 degree higher ROM than women. Less than 10 percent of men needed manipulation six weeks after surgery, compared to 18.5 percent for women.

"Our study reinforces the drain that obesity is having on the healthcare system," said Dr. Westrich. "The obesity epidemic is causing healthcare expenditures to grow at a rapid rate. Insurance companies, Medicare, hospital administrators, and patients need to understand that obesity will likely cause different patient outcomes, including more complications which may require further surgical interventions."  Also Dr. Westrich concludes that "setting realistic expectations prior to surgery is paramount to patient care."

Most patients who undergo total knee replacement are between 60 and 80 years old, but orthopaedic surgeons evaluate patients individually. Recommendations for surgery are based on a patient's pain and disability, not age. Total knee replacements have been performed successfully at all ages, from the young teenager with juvenile arthritis to the elderly patient with degenerative arthritis. Surgeons performed more than 533,000 knee replacements in 2005.


About HSS | Hospital for Special Surgery
HSS is the world’s leading academic medical center focused on musculoskeletal health. At its core is Hospital for Special Surgery, nationally ranked No. 1 in orthopedics (for the eighth consecutive year) and No. 3 in rheumatology by U.S. News & World Report (2017-2018). Founded in 1863, the Hospital has one of the lowest infection rates in the country and was the first in New York State to receive Magnet Recognition for Excellence in Nursing Service from the American Nurses Credentialing Center four consecutive times. The global standard total knee replacement was developed at HSS in 1969. An affiliate of Weill Cornell Medical College, HSS has a main campus in New York City and facilities in New Jersey, Connecticut and in the Long Island and Westchester County regions of New York State. In 2017 HSS provided care to 135,000 patients and performed more than 32,000 surgical procedures. People from all 50 U.S. states and 80 countries travelled to receive care at HSS. In addition to patient care, HSS leads the field in research, innovation and education. The HSS Research Institute comprises 20 laboratories and 300 staff members focused on leading the advancement of musculoskeletal health through prevention of degeneration, tissue repair and tissue regeneration. The HSS Global Innovation Institute was formed in 2016 to realize the potential of new drugs, therapeutics and devices. The culture of innovation is accelerating at HSS as 130 new idea submissions were made to the Global Innovation Institute in 2017 (almost 3x the submissions in 2015). The HSS Education Institute is the world’s leading provider of education on the topic on musculoskeletal health, with its online learning platform offering more than 600 courses to more than 21,000 medical professional members worldwide. Through HSS Global Ventures, the institution is collaborating with medical centers and other organizations to advance the quality and value of musculoskeletal care and to make world-class HSS care more widely accessible nationally and internationally.


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