Both overweight and obese patients with knee osteoarthritis (OA) are more likely to get knee replacement surgery, compared with normal-weight patients with knee OA, results of a population-based cohort study of people in Catalonia, Spain, suggest.
The study included 105,189 patients, who had been diagnosed with knee OA between 2006 and 2011. Patients with a history of knee OA or knee replacement in either knee before Jan. 1, 2006, and patients with a history inflammatory arthritis were not included in the study.
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The patients were followed from the date of knee OA diagnosis until the date they underwent elective knee replacement surgery or until Dec. 31, 2011. (The researchers were unable to follow up with all individuals initially enrolled in the study.) The participants were broken up into the following categories based on their body mass index: normal (BMI was less than 25 kg/m2), overweight (BMI was 25 to less than 30 kg/m2), obese class I (BMI was 30 to less than 35 kg/m2), obese class II (BMI was 35 to less than 40 kg/m2), and obese class III (BMI was greater than or equal to 40 kg/m2).
The risk of knee replacement increased with BMI. For patients with a normal weight, the incidence rates of surgery were 1.35/100 person-years, compared with 3.49/100 person-years in patients in obese class III. Adjusted hazard ratios for knee replacement surgery were 1.41 for overweight, 1.97 for obese class I, 2.39 for obese class II, and 2.67 for obese class III, compared with normal-weight study participants.
An additional finding was a significant interaction between BMI and age on the risk of knee replacement (P is less than .001), with a higher relative hazard associated with obesity among patients aged less than 68 years.
“This research demonstrates that overweight and obesity are strong independent predictors of the clinical progression of knee OA, from disease onset/diagnosis to joint failure and subsequent [knee replacement]. Overweight subjects are at over 40% increased risk of surgery, and those who are obese have a more than doubled risk when compared to subjects with normal weight,” said Kristen M. Leyland, D.Phil., and her colleagues.
Read the full study in Arthritis & Rheumatology (doi: 10.1002/art.39486).