Sensitivity and associations with pain and body weight of an MRI definition of knee osteoarthritis compared with radiographic Kellgren and Lawrence criteria: a population-based study in middle-aged females

Objectives: Is a magnetic resonance imaging (MRI) definition for tibiofemoral osteoarthritis [(TFOAMRI) (definite osteophyte and full-thickness cartilage loss (or a combination of these factors with other MRI osteoarthritis (OA) features)] more sensitive to detect structural OA compared with the Kellgren & Lawrence (K&L) grading? And which definition shows the strongest association with (1) knee pain at baseline, (2) persistent knee pain during 2-year follow-up, (3) new onset of knee pain ±2 years later, and (4) body mass index (BMI).

Design: Of 888 females of the open population Rotterdam Study, radiographs and MRI of both knees were assessed for knee OA defined by K&L ≥ 2 and TFOAMRI. Pain in or around the knee is measured at baseline and ±2 years later. GEE analyses are used for the associations.

Results: Of 1766 knees, 77 knees (4%) were diagnosed with K&L ≥ 2, whereas 160 knees (9%) met the TFOAMRI criteria. Only 43 knees met both definitions (34 knees were graded with K&L ≥ 2 and no TFOAMRI and 117 knees met only the TFOAMRI criteria). The association between the definitions and knee pain at baseline was higher when TFOAMRI was included [TFOAMRI alone: odds ratio (OR) = 2.83 (95% confidence interval (CI): 1.84-4.36); TFOAMRI & K&L ≥ 2: OR = 6.28 (95% CI: 2.99-13.19)] than for K&L ≥ 2 alone (OR = 1.83 (95% CI: 0.63-5.32)). This was similar for the association between the definitions and persistent knee pain, and between the definitions and BMI.

Conclusions: TFOAMRI detects more cases of knee OA than K&L ≥ 2. Together with a better content validity and at least equal construct validity, we conclude that the TFOAMRI definition for knee OA is more sensitive in detecting structural knee OA.