Study Finds No Correlation Between Smoking and Knee OA

A cross-sectional study published in BMC Musculoskeletal Disorders did not find a relationship between smoking and osteoarthritis (OA) of the knee.

“An inverse association between smoking and knee osteoarthritis (OA) has been suggested to exist, meaning that smoking may be protective of OA,” the study authors wrote.

“Therefore, the purpose of this study was to examine whether there is a relationship between smoking and early or more established knee OA in a cohort of patients with meniscal tears.”

Between Feb. 1, 2013, and Jan. 31, 2015 a total of 620 patients (mean age, 49.2 [18.0–76.8] years) undergoing knee arthroscopy for a meniscal tear were recruited from the Knee Arthroscopy Cohort Southern Denmark. Patients were selected from four different Denmark hospitals. Early or established knee OA was defined as combined patient-reported frequent knee pain, degenerative meniscal tissue, and cartilage defect presence as determined by the operating surgeons. Patients were excluded if they reported planned or previous anterior or posterior cruciate ligament reconstruction in either knee or a fracture to either leg six months prior to recruitment, or if they could not complete the questionnaire.

Preoperative Questionnaire

Smoking status was the primary exposure, which was obtained via an emailed questionnaire prior to surgery (median seven [three–10] days prior to surgery). Patients were asked, “Do you smoke?” and could respond with “no,” “no, stopped within the last six months,” “yes, rarely,” “yes, 1-5 cigarettes a day,” “yes, 6-10 cigarettes a day,” “yes, 11-20 cigarettes a day,” “yes, more than 20 cigarettes a day,” or “yes, smoke pipe.” Because only 12 patients were former smokers, never and former smokers (those who reported “no” or “no, stopped within the last six months”) were both classified as non-smokers (n = 482). Current smokers (n = 138) were those who answered “yes” to smoking any amount of cigarettes or a pipe. Additionally, all patients disclosed their age, sex, education level, work status, body mass index (BMI), and physical activity during leisure time.

Patients also answered the Knee injury and Osteoarthritis Outcome Score (KOOS), which includes subscales for pain, symptoms, activities of daily living (ADL), sports and recreation function, and knee-related quality of life (QoL). Using a scale from zero to 100 points, zero represented extreme knee problems, while 100 indicated no knee problems.

No Significant Relationship Between Smoking and OA

Early or established knee OA presented in 37.7% of current smokers and 45% of non-smokers. Among the 269 knee OA patients, 37.2% had International Cartilage Repair Society (ICRS) grade 1 in at least two knee joint compartments or ICRS grade 2 in one compartment; 62.8% had ICRS grade 3 or 4 in at least one knee compartment. BMI and sex did not significantly impact results.

The researchers concluded that their data “found no relationship between current smoking and early or more established knee OA in a cohort of patients undergoing knee arthroscopy for a meniscal tear. Meniscal tears, cartilage defects and knee pain may be important markers of knee OA and represent a different phenotype of knee OA than has previously been studied in relation to smoking.”