Platelet-rich plasma and bone defect healing.

On activation, platelets secrete an array of growth factors that contribute to bone regeneration. Combining platelet-rich plasma (PRP) with bone graft substitutes has the potential to reduce or replace the reliance on autografts. Lack of standardization and improper use may contribute to the conflicting outcomes reported within both preclinical and clinical investigations using PRP. This study investigates the effect of PRP dose on bone augmentation. Eighty critical-sized defects were created in the cancellous bone of the medial proximal tibia and the distal femur of 20 five-year-old female sheep. The defects were treated with three doses of an autologous thrombin-activated PRP combined with a biphasic calcium phosphate (BCP) or autograft and empty defects. Radiography, micro-computed tomography, histology, histomorphometry, and fluorochrome bone labels were examined at 4 weeks. The empty defects did not spontaneously heal. The highest dose of PRP treatment had a significantly greater micro-CT bone volume/total volume compared with the BCP alone (PRP: 30.6%±1.8%; BCP: 24.5%±0.1%). All doses of PRP treatment were significantly greater than the BCP alone for histomorphometric new bone area (PRP: 14.5%±1.3%; BCP: 9.7%±1.5%) and bone ingrowth depth (PRP: 2288±210 μm; BCP:1151±268 μm). From week 2 onward, PRP had a significant effect on the weekly bone ingrowth compared with BCP; however, autografts had the highest amount of weekly fluorescent bone labeling. PRP induces new bone formation with a dose-dependent response at 4 weeks when used with a BCP in sheep.