Introduction: The etiopathogenesis of Modic changes is unresolved. Two proposed theories implicate trauma and sub-clinical infection. Traditionally, Modic changes have been defined and studied using magnetic resonance imaging alone. Being a pathology of subchondral bone, it is only natural that a CT scan will be reflective of bone changes better than MRI. With this in the background, we did a study to probe the pathophysiological basis of Modic change (MC) by multimodal imaging rather than by MRI alone.

Materials & Methods:  The study was done in three steps.  In Step 1, radiological signs found in documented mild infections and traumatic endplate fractures were identified by MRI and CT, and by careful elimination, three signs unique to infection and trauma were distilled. In step 2, by ranking Z score, appropriate positive values for infection and negative for trauma were assigned, and an ‘Infection Probability Score’ (IPS) was developed. The score’s ability to differentiate infection and traumatic endplate changes (EPC) was validated in further 30 patients (15 infections and 15 trauma).  In step 3. the score was applied to 80 non-specific low back pain patients (NSLBP), and the probability of EPC as a result of infection was assessed.

Results: The three unique signs for infection and scores were: involvement of end plates at both sides of the disc(+3), typical CT erosion patterns of the subchondral bone associated with infection(+2), and extensive reactive sclerosis(+1). Involvement of superior EP only(-3), single vertebral body edema(-2), and none or only rim sclerosis(-1) were the pure signs for traumatic EP changes. The confidence interval pointing towards infection was 65% for score 4, 79% for score 5, and 89% for score 6.  The mean IPS score for the 80 patients with MCs was 4.5. None of the patients with an MC had a negative score, thus excluding trauma as an etiology of MC.  

Conclusion: Inclusion of CT in evaluating MC helped to identify signs indicating a high probability of infective process for MC.  Contrary to the traditional belief that MCs are secondary inflammatory changes, the study findings indicated that blood-borne primary infective endplatitis might, in fact, be the cause of MC.