Bone Abstracts

Successful long-term, cementless fixation of human shoulder components in osteoporotic (OP) and osteoarthritic (OA) patients poses major challenges. The possibility that enhanced osseointegration may rely on both the region of bone targeted and its relationship with the vasculature remains unexplored. We hypothesise that bone cells derived from subchondral (SC), cortical (C) and trabecular (Trb) bone regions exhibit differing osteogenic potential, which will be diminished in bones from OP patients. Primary osteoblasts from SC, Trb, C explants were obtained from OP (n=3) and OA (n=4) human patients undergoing shoulder arthroplasty and cell growth and gene/protein expression levels determined. Cell proliferation studies consistently illustrated that osteoblasts from all sites in OA patients exhibited 20% (P<0.01) greater growth rates than from OP. Furthermore, osteoblasts from SC and C showed enhanced rates of proliferation, compared to Trb sites (P<0.05) in both OA and OP. Induction of osteogenic differentiation was found to promote greater increases in ALP activity and Osterix and Runx2 mRNA levels in Trb and SC, than in C bone osteoblasts (P<0.05) in OA patients; all OP sites exhibited significantly smaller increases in ALP activity (P<0.05). Vascular endothelial growth factor (VEGF) is an osteoblast-derived signal which couples osteogenesis and angiogenesis. We found that media conditioned by Trb osteoblasts from OA contain highest (21%) VEGF_165/121 levels (P<0.05). Additionally, osteoblasts from all OA sites exhibited significantly higher VEGF mRNA/protein levels than OP (P<0.05). Our data indicated: i) that osteoblasts from all osteoporotic bone sites are likely to be compromised in their osteogenic potential, with limited growth, differentiation and VEGF production and ii) that osteoblasts from trabecular bone exhibit least proliferation, but greatest differentiation and pro-angiogenic potential, suggesting that they may provide for superior osseointegration. Together, these findings suggest that human osteoblasts with distinct positional origins exhibit divergent osteogenic potential.