To evaluate in patients with knee osteoarthritis (OA) the size changes in bone oedema and cysts over 24 months, and to contrast these changes with cartilage volume loss using quantitative magnetic resonance imaging.
107 patients with knee OA, selected from a large trial evaluating the effect of a bisphosphonate, were analysed by magnetic resonance imaging at baseline and 24 months. Assessments of subchondral bone oedema and cysts, and cartilage volume were done.
At baseline, 86 patients showed the presence of at least one type of bone lesion: 71 oedema, 61 cysts and 51 both. At 24 months, although not statistically significant, the oedema total size change increased by 2.09 (SD 15.03) mm, and the cyst by 1.09 (8.13) mm; mean size change for the oedema was +0.38 (2.18) mm and -0.10 (4.36) mm for the cyst. When analysed according to subregions, an increase was found for the cyst size in the trochlea (+0.67 (2.74) mm, p = 0.02) and in the lateral tibial plateau (+0.15 (0.83) mm, p = 0.09), and for the oedema size in the medial tibial plateau (+1.73 (8.11) mm, p = 0.05). At 24 months, significant correlations were seen between the loss of cartilage volume and oedema size change in the medial condyle (-0.40, p = 0.0001) and the medial tibial plateau (-0.23, p = 0.03), and the changes in cyst size in the medial condyle (-0.29, p = 0.01). A multivariate analysis showed that the oedema size change was strongly and independently associated with medial cartilage volume loss (-0.31, p = 0.0004).
These data demonstrate that bone lesions are prevalent in knee OA. The correlation of the oedema and cyst size increase in the medial compartment over time with a greater loss of cartilage volume in this area underlines the importance of subchondral bone lesions in OA pathophysiology.