Existing arthritis worsens when poorly aligned joints bear increased stress
People with a particular kind of knee alignment have a greater chance of developing osteoarthritis than do those with other types of leg alignment, reported researchers supported by the National Institutes of Health.
The study authors found that the higher risk occurred among those with an outward-facing alignment—knees relatively far apart and ankles closer together. Known as varus alignment, the knee configuration resembles bowleggedness, but is not as extreme.
Osteoarthritis results from the deterioration of cartilage, the hard, slippery material that cushions the ends of bone at the joints. The condition causes pain and often results in disability. According to the Centers for Disease Control and Prevention, osteoarthritis of the knees affects 6.1 percent of all adults over age 30.
The current finding, from a two and one half year study of nearly 3,000 people, may lead to the development of new ways to prevent osteoarthritis of the knee or lessen its symptoms.
The researchers also confirmed earlier findings that for people who have arthritis, varus alignment as well its opposite, the valgus, or inner facing, alignment contribute to worsening of the condition on the side of the knee bearing more stress.
“The study authors have shown that the varus alignment is a risk factor for osteoarthritis of the knees,” said Nancy Shinowara, Ph.D., a health scientist administrator in the National Center for Medical Rehabilitation Research of the NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD). “Future research may lead to new ways to reduce the stress that the condition places on knees and, in so doing, prevent osteoarthritis or lessen its severity.”
The study was published online in Annals of the Rheumatic Diseases. NIH’s National Institute of Aging also provided funding for the study.
First author Leena Sharma, M.D., of Northwestern University’s Feinberg School of Medicine in Chicago, conducted the study, with researchers there and at Boston University, the University of Alabama at Birmingham; the University of Iowa, Iowa City; Queens University in Kingston, Ontario; OAISYS, Inc., Kingston, Ontario; and the University of California, San Francisco.
The researchers followed 2,713 volunteers from Birmingham and Iowa City. The participants, from 50 to 79 years of age, had arthritis or were at increased risk of developing the condition because they were overweight, had a previous knee injury or previously had knee surgery.
Using X-rays of each participant’s legs, the researchers first measured the angle at which the upper and lower leg bones intersected at the knee—that is, the angle from the hip to the knee, to the ankle. Alignment that diverged more than two degrees in either direction from the 180 degrees straight leg alignment was considered valgus or varus. Participant’s knees were X-rayed when they entered the study, and again, two and one half years later.
The researchers also compared knee X-ray images taken at the study beginning with images taken two and a half years later. They examined them for tiny projections known as bone spurs and for thinning of cartilage, which are two telltale signs of arthritis. Using standard measurements, they rated the severity of new or worsening arthritis.
The research team found the varus stance was associated with 1.49 times the risk of developing arthritis compared with a straight-legged stance, whereas there was no increased risk for the valgus stance. The researchers statistically compensated for potentially complicating factors such as knee stability, muscle strength, and body weight.
Dr. Sharma explained that when someone walks on a healthy knee, about 70 percent of the force transmitted to the knee is focused on the inside. Varus alignment further increases the stress of impact on the inside of the knee, which may explain why this alignment was associated with an increased risk of developing osteoarthritis.
“Our results suggest the need to design interventions for people with varus alignment, in hopes of redistributing stress and possibly helping to prevent knee arthritis before it develops,” said Dr. Sharma.
The researchers also examined the effect of alignment in knees that were already arthritic. People with varus alignment were 3.59 times more likely to experience worsening of their condition on the inside of the knee, where stress is greatest, than those with a straight knee alignment.
Those with knee arthritis who had valgus alignment were 4.85 times more likely to experience worsening on the outside of the knee.
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The National Institutes of Health (NIH) — The Nation's Medical Research Agency — includes 27 Institutes and Centers and is a component of the U. S. Department of Health and Human Services. It is the primary federal agency for conducting and supporting basic, clinical, and translational medical research, and it investigates the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit http://www.nih.gov.