Background: Our purpose was to examine platelet-rich plasma (PRP) for its effect on bone formation and to follow the immunohistochemical changes in calcitonin gene-related peptide (CGRP) in dorsal root ganglion neurons innervating the discs as a possible index of nociceptive nerve transmission in a rat model.
Methods: A total of seventy rats were used. Ten constituted a non-punctured disc sham group, while another ten rats constituted a group that underwent puncture of the L4-L5 discs. Forty rats were in experimental groups in which the L4-L5 discs were punctured; posterolateral lumbar arthrodesis was performed with PRP (the PRP group) or without the use of PRP (the normal arthrodesis group), with twenty rats in each group. The remaining ten rats were used as blood donors. Four and eight weeks after surgery, microcomputed tomography examinations were done to evaluate the amount of bone and the L4-L5 spines were harvested to evaluate bone union, followed by resection of dorsal root ganglion neurons. The percentages of Fluoro-Gold-labeled and CGRP-immunoreactive neurons were calculated.
Results: The platelet count and the concentration of growth factors in PRP were higher than those in blood (p < 0.05). The bone volumes observed in the PRP group were significantly greater than those of the normal arthrodesis group at four and eight weeks (p < 0.05). Three (30%; 95% confidence interval [CI], 6% to 65%) of ten rats in the normal arthrodesis group and eight (80%; 95% CI, 44% to 98%) of ten rats in the PRP group were considered to have bone fusion four weeks after surgery (p < 0.05). At eight weeks, seven (70%; 95% CI, 34% to 94%) of ten rats in the normal arthrodesis group and nine (90%; 95% CI, 55% to 99%) of ten rats in the PRP group were considered to have bone fusion (p = 0.27). The proportion of CGRP-immunoreactive neurons was significantly greater in the punctured group than in the other groups. There were no significant differences between the normal arthrodesis group and the PRP group.
Conclusions: PRP appears to promote bone formation in rats and has a tendency to shorten the period of bone union in this rat model of posterolateral lumbar arthrodesis, but it did not influence the proportion of CGRP-immunoreactive neurons, a likely indicator of inflammatory pain originating from the degenerative intervertebral disc.
Clinical relevance: The ability of PRP in this model suggests that it may be able to shorten the period of union and lead to an early return to social activities after treatment.