Background/Purpose:

Early OA is a complex, poorly understood and still largely an unchartered “entity”. Thus, our purpose was evaluate the prevalence of findings suggestive of knee OA by MRI in middle-aged subjects without evidence of radiographic OA but with or without risk factors for OA.

Methods:

We selected 340 subjects from the Osteoarthritis Initiative, aged 45-55 years (51% women) with Kellgren Lawrence grade 0 in both knees, who had 3T knee MR images. Among them, 294 subjects had OA risk factors and 46 individuals were without risk factors (Table 1). Right knee MR images were assessed by one radiologist for osteophytes, cartilage damage, bone marrow lesions (BMLs), meniscal damage, synovitis-effusion and Hoffa synovitis using the MOAKS scoring system. Meniscal body extrusion was measured in mm, and we considered ≥3 mm as meniscal extrusion.

Results:

At least one MR-detected feature was found in 96% (281/294) of the subjects with OA risk factors and in 87% (40/46) of those without. Cartilage damage (82%), BMLs (60%), osteophytes (45%), meniscal body extrusion (32%), synovitis-effusion (29%) were the most common findings in subjects with OA risk factors, while cartilage damage (67%), osteophytes (46%), meniscal body extrusion (37%) and BMLs (35%) in subjects without. The prevalence of any abnormality was significantly higher in subjects with OA risk factors than in subjects without (prevalence ratio adjusted for age and sex 1.34 [95% CI 1.11, 1.62]), so was prevalence of subchondral cysts 2.11 (1.16, 3.84); BMLs 1.73 (1.15, 2.59), and cartilage lesions 1.22 (1.00, 1.50). Osteophytes, BMLs and subchondral cysts were observed more frequently in the patellofemoral joint than in the tibiofemoral compartments (Table 2).

Conclusion:

Our findings highlight the challenge to distinguish pathological features of knee OA from ‘normal’ ageing of the joint. Still, BMLs and cysts in particular were more frequently found in subjects having multiple OA risk factors than those without.

Table 1. Characteristics of the study participants.

Table 2. Prevalence of structural abnormalities on MRI in the right knees of the study subjects with and without knee OA risk factors; data are numbers and percentages in parentheses.