Researchers at Brown University have discovered that a protein found in the fluid surrounding cartilage acts as a shock absorber, a finding that could lead to better treatments for arthritis. The protein, called lubricin, is found in synovial fluid, a viscous substance inside joints. To learn more about its properties, Gregory Jay, associate professor of emergency medicine and the project’s leader, compared two samples of joint fluid: one normal and the other from a person with a rare disease in which the body does not make lubricin. The researchers implanted fluorescent beads in the fluids. Then they used a video camera to track the beads. The tracks enabled them to calculate the viscosity and other properties of the two fluids. They found that synovial fluid is more effective at protecting joints when lubricin binds to ­hyaluronate, a salt also found in the fluid. Hyaluronate injections are already used to treat arthritis; the researchers hope that augmenting them with lubricin will boost their protective power, shielding cartilage from damage. Jay’s team is preparing a therapy for animal testing.