While earlier studies have produced conflicting results, this well-conducted study using MRI scans of osteoarthritic knee joints shows fairly conclusive differences between smokers and non-smokers.

Making Knee Osteoarthritis Worse...

Summarized by Robert W. Griffith, MD
June 28, 2007

Summary

In a study of men with long-standing osteoarthritis of the knee, current smokers were more likely to have knee joint cartilage loss and more knee pain than non-smokers.

Introduction

Mayo Clinic researchers have uncovered an unusual cause of knee pain in people with osteoarthritis - smoking. Previous reports have associated cigarette smoking with chronic muscle and skeletal condition, such as low back pain and disk disease. The investigators studied men with symptom-producing knee osteoarthritis over 2½ years, and published their findings in the journal Annals of Rheumatic Diseases. Here's a summary of this study.

What was done

Enrollment of 324 patients was based on their "yes" answers to two questions: "Do you have pain, aching, or stiffness in one or both knees on most days?" and "Has a doctor ever told you that you have knee arthritis?" They had to be over 45, have an osteophyte (a small abnormal bony outgrowth) present on radiography of the knee and be able to walk - with a cane, if necessary. Not enough of the women enrollees smoked, so only men were included in the study proper. Five could not have magnetic resonance imaging (MRI), leaving 196 in the study.

Examinations done at baseline, 15 and 30 months included MRI of the knees and a questionnaire on the severity of their pain; at baseline and 15 months there was a standard questionnaire on smoking and a self-assessment of physical activity.

Three experienced readers examined all the MRI scans without knowledge of the patient's smoking status. Three different knee cartilages (tibiofemoral - medial, tibiofemoral - lateral, and patellofemoral) were scored for thickness and defects, resulting in scores of 0 to 4 according to the severity of changes, with 4 as the most severe.

The cartilage loss was analyzed using the 30-month follow-up data, unless unavailable, in which case the 15-month data were used. The same approach was used for pain information, scored on a 0 (no pain) to 100 (most severe pain possible) scale.

What was found

Of the 163 men with baseline MRIs, 4 were eliminated because their subsequent MRIs were unreadable for cartilage loss. The remaining 159 men were aged 68, on average, with a BMI of 30.5 (borderline obese).

At baseline, 19 men (12%) were smokers, averaging 21 cigarettes a day for an average of 45 years. During follow-up, 4 men quit smoking, and one took it up. Smokers tended to be younger (62 vs. 69 years) and leaner (28.9 vs. 31.3 BMI). They were physically less active, and had more knee pain than non-smokers.

The follow-up MRIs showed that current smokers were more likely to have cartilage loss at two of the three points measured - 3.5 times for the medial tibiofemoral and 2.4 times for the patellofemoral joints. There was no difference between the two groups for the lateral tibiofemoral joint.

Cigarette smokers had significantly higher pain scores at both baseline and at follow-up than non-smokers, but there was no difference between the development of pain during the study in either group.

Conclusions

This study showed fairly conclusively that current smokers are more likely to have knee joint cartilage loss and more knee pain than non-smokers. Previous studies (none of which used MRI to assess cartilage loss) have reported conflicting results. For instance, the Framingham Study examined the effect of previous smoking on the presence of knee osteoarthritis, and found smoking to have an apparent protective effect, even after making allowance for weight or BMI.¹ However, as the smokers in the study were less heavy, it's possible that long-term obesity among the non-smokers could have obscured the real effect.

The authors of the present study describe various possible mechanisms by which smoking might exert its effect on the knee joint cartilage. Further experimentation in humans as well as in animal models may help explain things better. The best approach, however, is for everyone - especially those with any degree of osteoarthritis - to quit smoking for good.

Source

• Cigarette smoking and the risk for cartilage loss and knee pain in men with knee osteoarthritis. S. Amin, A. Guermazi, M. Grigoryan,  et al., Ann Rheum Dis, 2007, vol. 66, pp. 18--22

Footnotes
1. Does smoking protect against osteoarthritis? DT. Felson, JJ. Anderson, A. Naimark ,  et al., Arthritis Rheum, 1989, vol. 32, pp. 166 --172

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