Objective: Given that obesity is a risk factor for knee osteoarthritis (OA), we asked whether progressively higher BMI's among obese women were associated with progressive increases in joint space narrowing (JSN).
Methods: Medial compartment JSN over 12 months in Lyon schuss radiographs of 60 obese women (BMI 30.0- 50.5) with radiographic and symptomatic OA was compared with that in 81 non-obese (BMI < 28) women with normal radiographs and minimal or no symptoms of knee OA.
Results: Among these OA patients, higher BMI tended to be associated with higher Kellgren and Lawrence grade (KLG) of OA severity. JSN in the non-obese controls was negligible, but in the 30 KLG 2 and 30 KLG 3 knees, JSN was 0.12 + 0.31 mm and 0.32 + 0.50 mm, respectively (p= 0.0045 and p < 0.0001). Among the OA patients, no association was seen between baseline BMI and 12-month JSN; indeed, the regression plot suggested a slight inverse relationship between the two.
Conclusions: Among these obese OA patients, progressively higher BMIs were not accompanied by progressively increasing rate of JSN. We did not evaluate joint loading, but it is possible that marked obesity limited the functional capacity of some OA subjects, protecting their knees from loading. For investigators considering eligibility criteria for a trial of a structure-modifying OA drug, these data suggest recruitment of patients with a BMI much greater than 30 will not enrich the sample in subjects who will have more rapid JSN than those with a BMI of only 30.