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, 2016, 9612437

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

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

Zhe Chen et al. Biomed Res Int.

Abstract

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.

Figures

Figure 1
Figure 1
The wild-type strain of P. acnes was isolated from the patient associated with severe disc degeneration and Modic change at the segment of L4~L5. (a)~(b) MRI examination of the patient showed signal intensity changes on the segment of L4~L5 at the cartilage endplate on T1WI and T2WI (a, b), suggesting a Modic change (b). Both were indicated by a white arrow. Meanwhile, severe disc degeneration and disc herniation were found at the same segment. (c) Gram's staining depicted a Gram-positive rod-shaped bacterium after three-day culture in anaerobic blood plate.
Figure 2
Figure 2
Signal changes were observed after the inoculation of the isolated wild-type strain of P. acnes and S. aureus. (a)~(b) Before the surgery, there was not any abnormality at T1WI and T2WI. (c)~(d) Since the second week, an obvious hypointense signal was observed on T1WI (c) and the hyperintense signal was found on T2WI (d) at the P. acnes-inoculated segment (L6~L7, indicated by a white arrow). Meantime, hyperintense signals of nucleus pulposus in T2WI disappeared, suggesting disc degeneration. (e)~(f) The signal changes remained constant until the eighth week at the end of follow-up. The volume of signal changes had increased from the second week to the eighth week. (g)~(h) The hyperintense signal changes were also observed in the S. aureus-inoculated segment (L6~L7, indicated by a white filled arrow) on T1WI (g) and T2WI (h); however, the definition of the endplates and vertebral body was less intact and more severe inflammatory signal changes were found. No significant signal changes were observed at the internal control segment of L5~L6 in all groups (indicated by a white triangle).
Figure 3
Figure 3
Eight weeks after the inoculation, P. acnes-inoculated intervertebral discs showed significant disc degeneration and endplates rupture but without severe discitis. (a) The intervertebral discs harvested from the TSB-inoculated internal control segment (L4~L5) had distinct nucleus pulposus and normal arranged annulus fibrosus. (b) The segment of wild-type strain of P. acnes-inoculated intervertebral discs (L6~L7) was demonstrated as disappearance of nucleus pulposus, endplates fracture (white arrow), disorganized annulus fibrosus, and partly cartilage proliferation. (c) By contrast, the intervertebral space significantly narrowed in S. aureus-infected intervertebral discs in coincidence with total cartilage tissue replacement and disappearance of nucleus pulposus and annulus fibrosus.

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