Knee Osteoarthritis to Increase in Younger Age Groups In Next Ten Years

Newswise — CHICAGO – Based on current trends, nearly 6.5 million Americans between the ages of 35 and 84 are expected to be diagnosed with knee osteoarthritis in the next 10 years, according to research presented this week at the American College of Rheumatology Annual Scientific Meeting in Chicago. The study also reports that people as young as 45 to 64 years old will account for more than half of newly-diagnosed cases – increasing the need for total knee replacements and placing an additional burden on the United States health care system.

Senior author of the study, Elena Losina, PhD, PhD; co-director of the Orthopedics and Arthritis Center for Outcomes Research at the Brigham and Women's Hospital in Boston and lead investigator of the study comments, “The large number of newly-diagnosed cases of knee osteoarthritis in younger individuals will lead to continued increases in the use of total knee replacement. Furthermore, these data are consistent with the recently observed tripling of total knee replacement use in 45 to 65 year old persons in the U.S.”

Osteoarthritis, or OA as it is commonly called, is the most common joint disease affecting middle-age and older people. It is characterized by progressive damage to the joint cartilage—the cushioning material at the end of long bones—and causes changes in the structures around the joint. These changes can include fluid accumulation, bony overgrowth, and loosening and weakness of muscles and tendons, all of which may limit movement and cause pain and swelling.

Researchers from the Brigham and Women's Hospital used data from the Centers for Disease Control in a validated computer model (called the OAPol model) of the course of knee osteoarthritis to estimate the number of newly-diagnosed knee OA cases in the U.S. during two decades: the 1990’s and the 2010’s.

Using the OAPol model, the researchers were able to simulate the onset and progression of knee OA in individuals with demographic characteristics similar to U.S.-based population from age 25 until death. Data from the model were combined with CDC population estimates to project the incidence and course of knee OA in the U.S. during the time periods studied.

The researchers found that physician-diagnosed knee OA affects about seven percent of Americans over the age of 45.They estimate that Americans will be diagnosed with knee OA much earlier in life in the 2010s versus the 1990s.In fact, the average age of physician-diagnosed knee OA is projected to fall from age 72 in the 1990s to age 56 in the 2010s – a difference of 16 years. Additionally, they found that Americans who are between the ages of 35 and 84 in the early 2010s are likely to account for nearly 6.5 million new cases of knee OA over the next decade, with ages 45 to 64 accounting for 59 percent of these cases.

The results further revealed that Americans ages 45 – 54 at the beginning of the 1990s would account for an estimated 412,214 newly-diagnosed knee OA cases over the following 10 years. Among this same age group, the study found that in the 2010s, newly-diagnosed knee OA cases over the next 10 years are expected to exceed two million. That means about five percent of all Americans ages 45 to 54 would be diagnosed with knee OA over the next decade of their life – compared to only 1.5 percent, based on the data from 1990s. “In the last decade, obesity and knee injuries have become more prevalent, possibly contributing to the increase in knee OA in younger adults,” explains Dr. Losina. “These trends toward earlier knee OA diagnosis may have a dramatic economic impact on the U.S. health care system.”

The American College of Rheumatology is an international professional medical society that represents more than 8,000 rheumatologists and rheumatology health professionals around the world. Its mission is to advance rheumatology. The ACR/ARHP Annual Scientific Meeting is the premier meeting in rheumatology. For more information about the meeting, visit www.rheumatology.org/education. Follow the meeting on Twitter by using the official hashtag: #ACR2011.

Editor’s Notes: Elena Losina, PhD, will present this research during the ACR Annual Scientific Meeting at McCormick Place Convention Center at 5:45 PM on Tuesday, November 8 in Room W 194b. Dr. Losina will be available for media questions and briefing at 8:30 AM on Monday, November 7 in the on-site press conference room, W 175C.

Despite these findings, exercise including sports has shown to relieve osteoarthritis pain. Learn more about how rheumatology health professionals are helping people complete Simple Tasks and live well with a rheumatic disease.

Presentation Number: 2510

Projecting the Future Public Health Impact of the Trend

Toward Earlier Onset of Knee Osteoarthritis in the Past 20 Years

Elena Losina (Brigham and Women's Hospital, Boston, Mass.)Sara A. Burbine (Brigham and Women's Hospital, Boston, Mass.)Alexander M. Weinstein (Brigham and Women's Hospital, Boston, Mass.)William M. Reichmann (Brigham and Women's Hospital, Boston, Mass.)Benjamin N. Rome (Brigham and Women's Hospital, Boston, Mass.)Jamie E. Collins (Brigham and Women's Hospital, Boston, Mass.)Jeffrey N. Katz (Brigham and Women's Hospital, Boston, Mass.)

Background/Purpose: Symptomatic knee osteoarthritis (OA) affects about 7% of Americans over the age of 45. Obesity and knee injuries have become more prevalent in recent years, which may contribute to increasing incidence of symptomatic knee OA, particularly in younger age groups. Temporal trends in the age of symptomatic knee OA onset and the resulting public health impact have yet to be studied.

Method: We used the OAPol Model, a validated computer simulation model of the natural history of knee OA, to estimate the age-stratified 10-year incidence of symptomatic physician-diagnosed knee OA during two distinct time periods (the 1990s vs. the 2010s). Symptomatic knee OA incidence data for the 1990s were derived from published literature. Data for the 2010s were derived from the National Health Interview Survey 2007-08. We followed a simulated cohort from age 25 to death to track the onset of symptomatic knee OA. We coupled model output and CDC population estimates from each time period to project the number of incident cases of knee OA in the US population over each 10-year period. We compared ages of OA onset and 10-year cumulative incidence of knee OA for the two time periods.

Result: The mean age of physician-diagnosed knee OA onset fell from 72 ± 12 years (mean ± standard deviation) in the 1990s to 56 ± 18 years in the 2010s. Americans ages 35-84 in the early 2010s were expected to incur 6,475,642 incident cases of symptomatic knee OA over the next decade, with those ages 45-64 accounting for 59% of these cases (Figure). Among Americans who were ages 45-54 at the beginning of the 1990s, an estimated 412,214 incident cases of knee OA were expected over the subsequent 10 years, resulting in a 10-year cumulative incidence of 1.5%. Among people in the same baseline age group in the 2010s, 2,108,881 incident cases of symptomatic knee OA are expected over the next 10 years, a cumulative incidence of 4.8%. The projected number of 10-year incident cases among those ages 65-74 at baseline decreased slightly between the 1990s (1,169,615 cases) and the 2010s (882,997 cases).

Conclusion: Since the early 1990s, the age of onset of physician-diagnosed symptomatic knee OA has shifted dramatically, occurring on average 16 years earlier in life. This trend may reflect temporal changes in the prevalence of OA risk factors, as well as thresholds for patient care-seeking and physician diagnosis of OA. If the current OA incidence trend continues, nearly 6.5 million Americans between the ages of 35 and 84 will be diagnosed with symptomatic knee OA in the next 10 years, with those ages 45-64 accounting for more than half of these incident cases. A resulting spike in the utilization of healthcare, specifically total knee replacements, could have a dramatic economic impact and place additional burden on the healthcare system.

Disclosures: S. A. Burbine, None.A. M. Weinstein, None.W. M. Reichmann, None.B. N. Rome, None.J. E. Collins, None.J. N. Katz, None.E. Losina, None.