Modic Changes and Disc Degeneration Caused by Inoculation of Propionibacterium acnes inside Intervertebral Discs of Rabbits: A Pilot Study

PURPOSE To investigate whether P. acnes could induce disc degeneration and Modic changes when inoculated into the discs of rabbits. METHOD A wild-type strain of P. acnes isolated from a patient associated with Modic change and disc degeneration was inoculated into the intervertebral discs of rabbits. Meanwhile, S. aureus was injected into the discs to establish a model of discitis as the comparison and a standard strain of P. acnes was inoculated as the control. MRI and histological change were observed. RESULTS Both the P. acnes-inoculated and S. aureus-inoculated rabbits showed hyperintense signals at endplates and hypointense signals at nucleus pulposus on T2WI. However, P. acnes only resulted in moderate disc degeneration and endplates rupture in histological examination, which was different from the pathological change of discitis caused by S. aureus. In addition, higher death rates (2/3 versus 0/5) were observed in S. aureus-inoculated rabbits. CONCLUSION Compared to S. aureus, the pathological change caused by P. acnes would be considered as Modic-I change and disc degeneration rather than a discitis.