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The Influence of Direct Inoculation of Propionibacterium acnes on Modic Changes in the Spine: Evidence from a Rabbit
Zhi Shan1, Xuyang Zhang, Shengyun Li
11Department of Orthopaedics, Sir Run Run Shaw Hospital, School of Medicine, Zhejiang University, Hangzhou, People's Republic of China.
Background:
Modic changes (inflammatory-like changes visible on magnetic resonance imaging [MRI] scans of a vertebral end plate) are common and are associated with low back pain, but their origin is unclear. To our knowledge, there have been no previous in vivo animal models of Modic changes. We hypothesized that Modic changes may be related to Propionibacterium acnes.
Methods:
Ten New Zealand White rabbits were injected percutaneously with 1 mL of P. acnes (1.6 × 10 colony forming units/mL) into the subchondral bone superior to the L4-L5 and L5-L6 discs; 10 other control rabbits received sham injections at L4-L5 and 1 mL of normal saline solution (vehicle) at L5-L6. The subchondral bone superior to L3-L4 discs was untreated (blank). Development of Modic changes was investigated with MRI studies before the operation and at 2 weeks and 1, 2, 3, and 6 months postoperatively. Following sacrifice of the rabbits, histological analysis and microcomputed tomography (micro-CT) were performed, and blood samples were analyzed. Cytokine expression in end-plate tissues was quantified using real-time polymerase chain reaction (PCR).
Results:
The group that received P. acnes showed significantly increased T1-weighted signal intensity at 6 months (mean and standard deviation, 3.43 ± 0.41 [range, 2.42 to 4.44] compared with 2.43 ± 0.66 [range, 1.98 to 2.87] before the injection) and higher T2-weighted signal intensity at 6 months. Positive culture results were obtained from 9 of 20 samples injected with P. acnes. Specimens with positive cultures had a higher prevalence of Modic changes (4 of 9 samples positive for P. acnes compared with 3 of 11 samples negative for P. acnes). Real-time PCR showed significantly increased expression of tumor necrosis factor-α, interleukin-1β, and interferon-γ following injection of P. acnes, but no changes were seen on histological analysis, micro-CT, or blood analysis.
Conclusions:
P. acnes can survive within the end-plate region and can initiate mild inflammatory-like responses from host cells, leading to signal intensity changes in MRI scans, which potentially resemble Modic changes.
Clinical Relevance:
Disc degeneration and low back pain are associated with Modic changes. Our results indicate that Modic changes can be associated with P. acnes in the conjunction area of the disc and subchondral bone. These results may be useful for understanding the underlying mechanisms of Modic changes and related pain.
Insights
Propionibacterium acnes (P. acnes) infection in rabbits induced Modic changes, which are inflammatory-like changes on MRI scans associated with low back pain. This study suggests P. acnes may play a role in Modic changes.
Area of Science:
- Spinal imaging and pathology
- Microbiology of bone infections
Background:
- Modic changes are common MRI findings in the spine, often linked to low back pain.
- The exact cause of Modic changes remains unclear, with limited in vivo animal models available.
- This study investigates the potential role of Propionibacterium acnes (P. acnes) in Modic changes.
Purpose of the Study:
- To establish an in vivo animal model for Modic changes.
- To investigate the association between P. acnes infection and Modic changes.
- To explore the inflammatory response triggered by P. acnes in the vertebral end plate.
Main Methods:
- New Zealand White rabbits underwent percutaneous injection of P. acnes or saline into the subchondral bone.
- Magnetic resonance imaging (MRI) was used to monitor Modic changes pre- and post-injection over six months.
- Histological analysis, micro-CT, blood analysis, and cytokine expression via real-time PCR were performed.
Main Results:
- P. acnes injection led to increased T1 and T2 signal intensity on MRI, indicative of Modic changes, at six months.
- P. acnes was cultured from injected samples, and positive cultures correlated with a higher prevalence of Modic changes.
- Increased expression of TNF-α, IL-1β, and IFN-γ was observed following P. acnes injection, but no significant histological or blood changes were noted.
Conclusions:
- P. acnes can survive in the vertebral end-plate region and elicit mild inflammatory responses.
- These responses can lead to MRI signal intensity changes resembling Modic changes.
- The findings suggest a potential link between P. acnes and Modic changes, offering insights into low back pain mechanisms.
