Propionibacterium acnes Incubation in the Discs Can Result in Time-Dependent Modic Changes

Study Design. A case-control study of animal model of Modic changes (MCs) on rabbits. Objective. To evaluate the feasibility of inducing of MCs by injection of Propionibacterium acne ( P. acnes ) into the lumbar intervertebral discs of rabbits. Summary of Background Data. MCs have been widely observed, and assume to be closely associated with low back pain and P. acnes , but there are few animal models showing the progression of MCs. Methods. Ten rabbits were used for the study. The L3–4 and L4–5 discs of all rabbits were injected with 100 μL P. acnes (1.6 × 10 7 CFU/mL) as P. acnes group, L2–3 disc were injected with 100 μL normal saline as vehicle, and L5–6 disc was untreated (blank). MCs were investigated by magnetic resonance imaging before operation and at 2 weeks, 1, 3, 4.5, 6, and 9 months postoperatively. Following sacrifice, histological analysis, blood test and micro-computed tomography were performed. Cytokine expression in nucleus and endplate tissues was quantified using real-time polymerase chain reaction. Results. From 3 months postoperatively, the P. acnes group showed significantly decreased T1-weighted signal intensity, whereas the T2-weighted signal was significantly higher at 3 and 4.5 months, and then decreased remarkably at 6 and 9 months. Eleven of 20 inferior endplates were identified as type I MCs at 4.5 months, and 9 of 20 were identified as type II MCs at 9 months. Real-time polymerase chain reaction showed that expression of interleukin-1β, tumor necrosis factor α, interferon-γ, matrix metalloproteinase-9, and thrombospondin motifs-5 in the nucleus pulposus, and interleukin-1β, tumor necrosis factor α, and thrombospondin motifs-5 in the endplates, were significantly upregulated after injection of P. acnes . Histological slices of discs injected with P. acnes showed disc degeneration, endplate abnormalities, and inflammatory response, with micro-computed tomography confirming bone resorption. Conclusion. P. acnes infection of the disc can induce degeneration of the disc and an inflammatory response in the endplate region, presenting as MCs type I and II time dependently. Level of Evidence: N/A