Men who smoke have a higher risk of arthritis in the knee, showing faster loss of cartilage than non-smokers, a new study suggests.

"This is a novel finding," said Dr. Shreyasee Amin, a clinical rheumatlogist at the Mayo Clinic in Rochester, Minn., who led the study.

"Previous studies showed no association between cigarette smoking and knee osteoarthritis or even a protective effect of smoking."

Osteoarthritis is a degenerative joint condition that commonly affects the fingers and knees, and is one of the leading causes of disability in seniors. Pain and stiffness in the joints are the main symptoms.

The team looked at 159 men with arthritis of the knee for 30 months. Participants were given three MRI scans, a more sensitive imaging technique than those used in previous studies.

About 12 per cent of the participants, or 19 men, were active smokers who smoked an average of 20 cigarettes a day for an average of 40 years.

Risk of cartilage loss at the medial tibiofemoral joint — which connects the thighbone and shinbone — rose 2.3-fold among current smokers, compared with the men who had quit smoking or never smoked, the team reports in this week's online issue of the Annals of the Rheumatic Diseases.

Cartilage is the elastic tissue cushioning the ends of bones. 

Risk of cartilage loss at the patellofemoral joint — found between the knee cap and thigh bone — increased 2.5-fold compared with nonsmokers, the study showed.

"Smoking may alter the pain threshold," the researchers said. "It also increases the levels of toxic substances in the blood and starves tissues of oxygen, which may hasten the loss of cartilage."

Cigarette smoke may also damage cells in the knee cartilage, they said.