ROCHESTER, Minn.—Men with knee osteoarthritis (OA) who smoke experience greater cartilage loss and more severe pain than men who do not smoke, according to a new study published online in the Annals of the Rheumatic Diseases.1

"Previous studies showed no association between cigarette smoking and knee OA, or even [suggested] a protective effect of smoking." —Shreyasee Amin, MD.
Shreyasee Amin, MD, rheumatologist at the Mayo Clinic in Rochester, Minnesota, and colleagues, examined 159 men with symptomatic knee OA who were taking part in the Boston Osteoarthritis of the Knee Study. The researchers examined results of magnetic resonance imaging (MRI) of the more symptomatic knee for each patient at the study's inception and again at 15 and 30 months. Cartilage loss was determined at the tibiofemoral joint and the patellofemoral joint in the knees. The Visual Analog Scale (VAS) pain score was used to assess pain.

Nineteen, or 12%, of the men were current smokers when the study began. Current smokers had a 2.3-fold increased risk of cartilage loss at the medial tibiofemoral joint and a 2.5-fold increased risk of cartilage loss at the patellofemoral joint, compared to the men who had quit smoking or never smoked. Current smokers also had higher pain scores than men who were not current smokers. At the beginning of the study, smokers scored 60.5 on the VAS vs 45.0 among non-smokers. At follow-up, smokers scored 59.4 on VAS compared with 44.3 among their non-smoking peers. The findings held after researchers controlled for the fact that smokers were leaner and younger than other study participants.

"This is a novel finding," Dr. Amin has announced. "Previous studies showed no association between cigarette smoking and knee OA, or even [suggested] a protective effect of smoking."

Possible mechanisms cited

Exactly how smoking affects cartilage loss is not fully understood, but several factors could be at play. For example, smoking may inhibit cell proliferation in the knee cartilage, decrease oxidant stress, and/or raise carbon monoxide levels in arterial blood, contributing to tissue hypoxia, which could impair cartilage repair, the study authors speculate.

The increased pain may be associated with the effect of smoking on other knee joint structures mediating knee pain or smoking may affect the pain threshold for knee or other musculoskeletal pain, they write.

Welcome addition to the literature on smoking and OA

The new study "broadens our knowledge in this area by employing a highly sensitive OA progression assessment method," says Frances V. Wilder, PhD, executive director of the Arthritis Research Institute of America, Inc, based in Clearwater, Florida. "The use of MRI, along with three blinded readers, contributes to the strength of the study methodology. Such sensitivity could afford the ability to detect changes in articular cartilage, possibly due to cigarette smoking, over a 30-month time period," said Wilder, who reviewed the study for CIAOMed.

Overall, "[Dr.] Amin and colleagues presented an excellent study with sound methodology [and] their design and subsequent findings have advanced our knowledge base in this important area of study," she said. "Their results suggest cigarette smoking has a deleterious effect on patients with knee OA; these data add to the growing arsenal of information clinicians can reference as they encourage their patients to evaluate the consequences of this modifiable risk factor."

Reference

1. Amin S, Niu J, Guermazi A, et al. Cigarette smoking and the risk for cartilage loss and knee pain in men with knee osteoarthritis. Ann Rheum Dis. 2006 December 20; [Epub ahead of print].