Microstructural and cellular characterisation of the subchondral trabecular bone in human knee and hip osteoarthritis using synchrotron tomography

Objective It is unclear if different factors influence osteoarthritis (OA) progression and the changes characterising OA disease in hip and knee. We investigated the difference between hip OA and knee OA at the subchondral bone tissue and cellular level, relative to the degree of cartilage degeneration.

Design Bone samples were collected from 11 patients (aged 70±8 years) undergoing knee arthroplasty and 8 patients (aged 64±12 years) undergoing hip arthroplasty surgery. Bone microstructure, osteocyte-lacunar network and bone matrix vascularity were evaluated using synchrotron micro-CT imaging. Samples were additionally examined histologically to determine osteocyte density, viability, and connectivity.

Results After adjustment for donor gender and age, associations between the extent of cartilage degeneration, bone volume fraction [8.7, 95% CI (3.4, 14.1)], trabecular number [1.5, 95% CI (0.8, 2.3)], osteocyte lacunar density [4714.9; 95% CI (2079.1, 7350.6)] and trabecular separation [-0.06, 95% CI (0.01, 0.1)] were found in both knee and hip OA.

When compared to knee OA, hip OA was characterised by higher trabecular thickness [0.006, 95% CI (-4, 0.01)], larger but less spheric osteocyte lacunae [47.3; 95% CI (11.2, 83.4), -0.04; 95% CI (-0.6, -0.01), respectively], lower vascular canal density [-22.8; 95% CI (-35.4, -10.3)] lower osteocyte density [-84.9; 95% CI (-102.4, -67.4)], and less senescent but more apoptotic osteocytes [-2.4; 95% CI (-3.6, -1.2), 24.9; 95% CI (17.7, 32.1)], respectively.

Conclusion Subchondral bone from hip OA and knee OA exhibits different characteristics at the tissue and cellular levels, suggesting different mechanisms of OA progression between the hip and knee joints.