Severity of Bone Marrow Edema on MRI Predicts the Diagnostic Potential of Foot Joint Injections.

Background: Intraarticular steroid and local anesthetic injections are often performed for foot pain. Localizing the exact joint acting as a pain generator in foot pain is eminent for optimal and cost-effective treatment. Because of the complex anatomy of the foot with multiple small articulations side by side, this can be challenging. This study's purpose was to determine magnetic resonance imaging (MRI) findings as possible predictive factors for the immediate outcome of intraarticular injections of the foot.

Methods: All single joint foot injections at our institution from January 2019 to May 2020 with prior MRI scans were included in this retrospective study. Visual analog scale (VAS) pain assessments before and after injection, relative change in pain scores and indication were recorded. All MRIs were retrospectively analyzed by 2 blinded radiologists regarding the presence and severity of subchondral bone marrow edema (BME), subchondral cysts, cartilage defects, osteophytes, joint effusion, and soft tissue edema. Spearman analysis was used to assess correlation between MRI findings and pain relief. Interrater variability was assessed using weighted Cohen κ analysis.

Results: A total of 164 injections from 162 patients were included (mean age, 53 years ± 15.5, 99 females). Relative pain reduction correlated significantly with BME severity (P < .05). Interrater reliability assessing BME was excellent (weighted Cohen κ 0.863).

Conclusion: The degree of pain reduction after intraarticular foot injections correlates significantly with the severity of subchondral bone marrow edema-like signal on MRI before injection.