The objective of the study was to determine articular cartilage and subchondral bone expression of the bone regulating molecules receptor activator of nuclear factor κB ligand (RANKL), receptor activator of nuclear factor κB (RANK) and osteoprotegerin (OPG) in the hip osteoarthritis (OA) and hip osteoporosis (OP). Cartilage and subchondral bone samples were obtained from 40 patients undergoing total hip replacement surgery after end stage of ostearthritis (15 patients) or femoral neck fracture (25 patients). Tissue sections were stained with Safranin O and graded. Immunohistochemical staining was then performed, and levels of RANKL, RANK and OPG expression were assessed using a semi-quantitative scoring system. In addition, levels of mRNA encoding for RANKL, RANK and OPG were determined by a real-time reverse transcription-polymerase chain reaction technique. We found that expression of RANKL protein, mRNA expression, and the ratio of RANKL: OPG mRNA was greater in the cartilage and subchondral bone in OA samples in comparison with OP samples (P < 0.05). Increased RANKL and staining in OA cartilage was predominantly in the peri-cellular region of the middle and deep zones as well as in the matrix of the superficial zone. OPG mRNA expression in OA samples was greater in the cartilage in comparison with subchondral bone (P < 0.05) while OPG mRNA expression in OP samples was greater in the subchondral bone in comparison with cartilage (P < 0.05). Cartilage and subchondral bone are in close proximity and soluble proteins produced in the cartilage are likely to move from one compartment to the other. Our finding of increased expression of RANKL in OA cartilage might explain the increase in bone turnover reported in the subchondral bone of OA patients.
Disclosure: The authors declared no competing interests.