Association between inflammation from knee injuries and a progressive loss of joint lubrication

Researchers have found an association between inflammation from knee injuries and a progressive loss of joint lubrication, which may predispose people to arthritis. They have also found a way to quantify how much lubrication is lost following injury.

The results, which appear in the June issue of Arthritis & Rheumatism, are from a study by Rhode Island Hospital, University of Rhode Island, and Case Western Reserve University School of Medicine.

It is known that injury is a risk factor for osteoarthritis, a common condition that erodes cartilage and primarily affects people later in life, and that putting weight on an injured knee can result in increased friction and cause cartilage damage. But it is not known how changes in lubrication can positively or negatively impact cartilage damage.

"If you injure a joint, or have been injured in the past, it would be useful to have a test that could indicate your level of risk for developing arthritis," says author Gregory D. Jay, MD, PhD, research director in emergency medicine at Rhode Island Hospital and associate professor of emergency medicine and engineering at Brown University. "In this study, we were able to quantify loss of lubrication – which has important implications for preventing osteoarthritis."

Researchers first looked at rabbits with injured knees. They withdrew synovial fluid surrounding the knee cartilage and measured lubricin, a naturally-produced substance that protects the joint from wear. They found that lubricin completely disappeared from the rabbits in three weeks.

An observation of emergency room patients supported many of the findings observed with rabbits. Researchers took a retrospective look at the synovial fluid drawn from injured knees of emergency room patients to alleviate swelling. There was a wide range of lubricating ability, but overall, there was greater friction than in patients with no injuries. In addition, the study found an increase in production of CII peptides, which indicates early damage to joint cartilage.

At the opposite end of the spectrum, researchers looked at patients with rheumatoid arthritis, chronic inflammation caused by an autoimmune reaction against the body's own tissues. They found that patients with rheumatoid arthritis had no lubricating ability. The findings indicate that the deterioration of lubricating ability and its possible association to cartilage damage "is not a unique feature of early stages of a knee injury, but rather a common feature in inflammatory conditions, both acute and chronic," the paper states.

In order to measure the breakdown of lubricin, researchers developed a simple test that can be performed in any hospital laboratory, Jay says. Previously, friction tests were conducted with complex machines that are not easily accessible to physicians.

The next step is to conduct a study with patients, Jay says, to determine whether patients with injuries should stay off their feet.

"Our ultimate goal is to determine how much lubrication is lost after a knee injury. If you're walking on a non-lubricated joint, it's very likely you'll develop osteoarthritis or induce damage to other areas of the knee," Jay says.