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Prospective investigation using a posterolateral spinal fusion (PLSF) model in rabbits.To assess the effects of platelet-rich plasma (PRP) alone, or with uncultured bone marrow, on bone ingrowth and angiogenesis in experimental PLSF.PRP is an autologous substance potentially beneficial to spinal fusion, because it includes several growth factors that may stimulate bone ingrowth and angiogenesis. However, the results of experimental and clinical investigations on the effectiveness of PRP in spinal fusion are controversial. This study was aimed at analyzing the influence of PRP on bone ingrowth and angiogenesis in experimental PLSF.Twenty White New Zealand rabbits underwent PLSF at L4–L5 level. The graft material included a ceramic carrier (Pro-Osteon 500R) loaded, in 7 rabbits, with PRP alone on the right side (Group 1A) and with uncultured bone marrow in the left side (Group 1B). In 7 rabbits, the ceramic carrier was used alone in the right side (Group 2A), and with uncultured bone marrow in the left side (Group 2B). Six rabbits (Group 3) were sham operated on both right and left sides. Six months after surgery, the lumbar spine was harvested en bloc and evaluated by high-resolution radiographs (Faxitron, Wheeling, IL) and histology.The radiographical outcome showed a fusion rate of 86% in Groups 1A, 1B, and 2B and a fusion rate of 71% in Group 2A. No specimen showed a solid fusion in the sham group. Histological analysis revealed new bone formation in the periapophyseal area in Groups 1 and 2, but a complete bony bridge between the transverse processes was not observed in any specimen. In all groups, vascular density was significantly greater in the peri- compared with the interapophyseal region. In the PRP group, there was no evidence of increased vascular density in the grafted material compared with the other groups.In experimental PLSF model in rabbits, PRP was not effective in promoting new bone formation and vascularization.