Changes in the intervertebral disc height index (DHI). Four weeks after anular puncture [Punc. (at -4 weeks)], phosphate-buffered saline (PBS) (control) or platelet-poor plasma (PPP)- or platelet-rich plasma (PRP)-releasate was injected into the punctured discs. The percentage DHI was measured at each time point to quantify changes in disc height. Four weeks after the injection of PRP-releasate, the percentage DHI of injected discs in the PRP group was significantly higher than that in the PBS group (P <0.01, repeated analysis of variance). This significant difference in the percentage DHI was sustained until 8 weeks after the injection. Values are shown as mean ± standard error of the mean. *P <0.05, **P <0.01 versus PBS group; #P <0.05, ##P <0.01 between PPP and PRP.