Osteocyte lacunar and cellular characteristics in the subchondral bone plate and trabecular bone of human knee osteoarthritis.

BACKGROUND: Subchondral bone (SB) plays a critical role in the development of osteoarthritis (OA), yet the structural and cellular organisation of osteocytes within subchondral compartments remains poorly characterised. This study investigated osteocyte lacunar morphology and cellular characteristics in human knee OA. METHODS: 16 osteochondral biopsies were obtained from nine patients undergoing primary knee arthroplasty for end-stage OA. Synchrotron radiation micro-computed tomography was used to quantify attenuation-based relative mineral density (RMD) and osteocyte lacunar morphometry within the SB plate and trabecular bone compartments. Histological analyses were performed to assess osteocyte viability, apoptosis, senescence, and canalicular network parameters. RESULTS: Paired analysis demonstrated compartment-specific differences between the SB plate and trabecular bone. The SB plate exhibited higher RMD and vascular canal density (p = 0.03) and greater lacunar density (p = 0.01) compared with trabecular bone. Lacunae within the SB plate were smaller (p = 0.01) and less spherical (p = 0.003), than those in trabecular bone. Osteocyte viability was reduced in the SB plate (p = 0.02) and was accompanied by increased apoptosis (p = 0.01) and senescence (p = 0.03). In contrast, canalicular number and length did not differ significantly between compartments. CONCLUSIONS: High-resolution synchrotron imaging, combined with histological assessment, demonstrated compartment-specific differences in osteocyte lacunar morphology and cellular characteristics between the SB plate and trabecular bone in advanced human knee OA. These findings highlight compartment-specific structural and cellular heterogeneity within osteoarthritic SB and emphasise the importance of considering subchondral compartments separately when investigating cellular organisation within the osteochondral unit.