Fig. 1
Correlation between CC and histological OA grade by OARSI (a), between CC and age (b) and between CC and BMI (c). The scatter diagrams (data points are jittered to avoid overplotting) show the relation between the mean amount of cartilage calcification (in % of total cartilage area) and histological OA grade by OARSI (a), respectively age in years (b) and BMI (c). For better overview, the y-axis is displayed on a logarithmic scale. The scatter diagram A is shown with an orthogonal linear regression line (blue line). The mean amount of cartilage calcification correlated significantly with the histological OA grade (a) (rs = 0.51, 95 %-CI[0.32, 0.65], p < 0.001) but not with age (b) (rs = 0.20, 95 %-CI[−0.02, 0.40], p = 0.07) or BMI (c) (rs = −0.07, 95 %-CI[−0.17, 0.14], p = 0.51)