ABSTRACT Background Modic changes (MC) are painful vertebral bone marrow lesions. Three interconvertible types represent different pathology stages with MC1 being the most painful, MC2 less painful, and MC3 asymptomatic. Bacterial ( Cutibacterium acnes ( C. acnes )–mediated) and non‐bacterial etiologies are both suggested to induce MC1, but it remains unclear whether MC conversion is etiology‐specific. This has important implications for patient management and the development of MC therapies. Aims To assess MC‐subtype lesion prevalence and pain‐like behavior over time in an etiology‐specific MC rat model. Methods Four‐to‐five‐month‐old Sprague–Dawley rats underwent sham ( n = 12) surgery or endplate injury followed by an intradiscal injection of 2.5 μL of either TNF‐α (1000 ng/mL PBS) ( n = 19) or C. acnes (3.2 × 10 8 CFU/mL in PBS) ( n = 18) to mimic aspects of bacterial versus non‐bacterial MC etiologies. MC‐subtype prevalence was evaluated by magnetic resonance imaging at 1, 8, and 14 weeks post‐injury. Disc degeneration, bone marrow lesion neutrophil elastase and CD19 immunoreactivity, spinal cord sensitization, and pain‐like behavior (von Frey) were assessed, and contributors to pain‐like behavior were identified (random forest). Results C. acnes injection caused higher MC1‐like lesion prevalence than TNF‐α and Sham at all‐time points and higher spinal cord substance P expression at 14 weeks post‐injury. MC2‐like lesions increased over time in TNF‐α‐injected discs and were more prevalent at 14 weeks post‐injury than C. acnes . C. acnes injection resulted in bone marrow lesions with higher neutrophil elastase‐ and CD19 immunoreactivity. MC1‐like lesions contributed strongest to pain‐like behavior, although von Frey did not differ between groups. Conclusion Intradiscal C. acnes injection sustained MC1‐like lesions in an etiology‐specific lumbar MC rat model, suggesting that patients with bacterial MC etiology may be more likely to persist in painful MC1.
Heggli et al. (Wed,) studied this question.