Subchondral bone cysts indicate osteopenia in advanced knee osteoarthritis

Abstract

INTRODUCTION: Subchondral bone cyst (SBC) was reported as a predictor for cartilage loss and the risk of knee replacement, yet little is known about its consequence in osteoarthritis (OA) pathophysiology. We investigated the impacts of SBC on surrounding bone and marrow tissues via micro-computed tomography (μCT) and histomorphometry. METHODS: A total of 144 advanced OA knee replacement patients were selected. Trabecular parameters of resected tibial plateaux were analysed on μCT. Ratios of marrow tissue to total marrow space were calculated by histomorphometry. RESULTS: A total of 98 patients were SBC+ and 46 were SBC-. Presence of SBC in tibial spine was correlated to mean (±standard deviation) values of low mineral density (SBC+: 0.63 ± 0.047 g/cm3 vs. SBC-: 0.65 ± 0.054 g/cm3, p=0.011), bone volume fraction (17.62 ± 7.31% vs. 20.36 ± 8.44%, p=0.047), surface to tissue density (3.41 ± 0.78 mm-1 vs. 3.87 ± 0.91 mm-1, p=0.004), trabecular number (0.92 ± 0.25 mm-1 vs. 1.07 ± 0.30 mm-1, p=0.004), connectivity (7.16 ± 3.28 mm-3 vs. 8.55 ± 3.47 mm-3, p=0.021), and increased trabecular separation (0.70 ± 0.10 mm vs. 0.64 ± 0.13 mm, p=0.004) in lateral compartment. The SBC+ samples also had higher tissue to marrow space ratio (21.9 ± 7.9%) than SBC- samples (11.1 ± 7.4%). CONCLUSION: Subchondral bone cyst occurred together with low bone mass and marrow fibrosis. Subchondral bone cyst could be a biomarker for subchondral osteopenia in knee OA.