Comparison of VEGF-producing cells in periprosthetic osteolysis.

The pro-angiogenic cytokine vascular endothelial growth factor (VEGF) has been implicated in periprosthetic osteolysis and subsequent aseptic loosening of implants following total hip arthroplasty (THA). The goal of this study was to investigate whether increased VEGF at the bone-implant interface is secondary to a greater number of VEGF-producing cells or to increased VEGF production by individual cells. Real time polymerase chain reaction (RT-PCR) techniques were used to assess the expression of VEGF mRNA (isoforms 121, 165, 189) in periprosthetic tissues from revision THAs. Immunofluorescence was used to determine both differences in overall cellularity and in VEGF-producing cell type (macrophages, fibroblasts, endothelial cells) between patients with periprosthetic osteolysis (OL) and a control group undergoing primary THA for osteoarthritis (OA). Quantitative analysis of VEGF release in periprosthetic membranes via RT-PCR demonstrated no significant difference in the per-cell mRNA production of VEGF isoforms 121 165, or 189 between OL and OA patient groups. Immunofluorescence showed both higher cellularity and higher overall VEGF expression in the OL group. Immunofluorescence also showed a significant increase in macrophages in the OL group, but no significant difference in the proportion of fibroblasts or endothelial cells between the OL and OA groups. Co-localization of CD68+ and CD11b+ macrophage fluorescent signals with VEGF signal was greater in the OL group than in the OA group. Our results demonstrate that increased VEGF in OL periprosthetic tissue compared to OA synovium is correlated to increased numbers of VEGF-producing CD68+ and CD11b+ macrophages. Impact statement: Aseptic loosening, caused in large part by OL, remains the major cause of failed THAs leading to revision surgery. At the bone-implant interface, we found increased numbers of macrophages-cellular mediators of OL-and increased VEGF expression. VEGF may be a possible target for therapeutic intervention in mitigating OL.