Bone Marrow Edema on MRI Predicts Immediate Outcome of Joint Infiltrations of the Foot

Purpose or Learning Objective: Intra-articular foot infiltrations can be performed as a diagnostic but also as a therapeutic option for pain relief in conditions such as osteoarthritis or impingement. Our purpose was to correlate magnetic resonance imaging (MRI) findings with immediate outcomes after intra-articular foot infiltrations. Methods or Background: In this retrospective study, patients who received a therapeutic intra-articular single-joint infiltration in the foot and had an MRI examination < 1 month before the infiltration were included. Visual analog scale (VAS) pain assessments before and 15 minutes after the infiltration were noted. Each patient's MRI was analyzed retrospectively by two blinded independent radiologists using a standardized form, assessing bone marrow edema, subchondral cyst formation, cartilage defects, soft tissue edema, subchondral sclerosis, osteophytes, and joint effusion. Interrater reliability was assessed using weighted Cohen's κ analysis. Spearman's analysis was used to assess correlation between each individual MRI finding for both readouts and the absolute and relative degree of pain relief. Results or Findings: A total of 192 infiltrations from 189 patients were included. Most frequent indications were osteoarthritis, impingement, or pain. The most common infiltrated articulation was the ankle joint, followed by the subtalar joint and metatarsophalangeal joint. Average pain reduction was − 2.65 points on VAS; average relative pain reduction was − 46%. In 24% of all infiltrations, no pain relief was achieved. Absolute immediate pain reduction correlated significantly with the severity of bone marrow edema (p < 0.05), subchondral cysts (p < 0.05), and cartilage defects (p < 0.05) for both readers. The interrater reliability to assess bone marrow edema was excellent (Cohen's κ = 0.847). Conclusion: Degree of acute pain reduction after intra-articular infiltration in the foot correlates significantly with severity of bone marrow edema, cartilage defects, and subchondral cyst formation on MRI before infiltration