Inflammation, a bodily mechanism which usually aids healing, has the opposite effect on the knee, according to new research.
Scientists from the Duke University Medical Centre believe their findings may lead to treatments for injuries or osteoarthritis in the knee.
They identified two immune system proteins that trigger inflammation, interleukin-1 (IL-1) and tumour necrosis factor (TNF). These proteins block the healing of protective tissue in the joint called the meniscus.
When counteractive agents were applied directly to the meniscus, the repair process resumed.
Farshid Guilak, senior member of the research team and director of orthopaedic research at Duke, said: "There already is a drug that blocks the effects of TNF that is used widely and effectively in patients with rheumatoid arthritis, the form of the disease caused by body's own immune system attacking the joint.
"Another drug also exists that blocks IL-1 that is being used for rheumatoid arthritis and is currently undergoing clinical trials for osteoarthritis."
The study appears in the September issue of the journal Arthritis & Rheumatism.