Incidental Finding of Plantar Plate Pathology on Routine Magnetic Resonance Imaging of the Foot and Ankle.

Background: We hypothesized that there would be a comparable and high incidence of an incidental torn plantar plate on routine magnetic resonance imaging (MRI) in asymptomatic patients.

Methods: We included adult patients undergoing a foot MRI from 2019 to 2020. Based on the documented reason for MRI, patients were divided into symptomatic and asymptomatic. A separate musculoskeletal radiologist re-evaluated MRI images. Findings were categorized as "torn vs intact." We also used the anatomical grading system (AGS).

Results: We reviewed 218 records, including 165 asymptomatic and 53 symptomatic patients. The chance of finding a plantar plate (PP) tear on MRI of symptomatic patients was 28% (21% in PP2, 5.7% in PP3, 5.7% in PP4, and 2% in PP5), while PP tear in asymptomatic patients was only apparent in 2% of MRIs (1.5% in PP2, 0 in PP3, 0 in PP4, and 0.6% in PP5). Cohen's kappa coefficient was 0.92, showing excellent agreement between the radiologists. Odds calculation revealed that the chance of finding a torn PP in an asymptomatic patient is 2.5%. In comparison, the chance of finding an intact PP in a symptomatic patient is 72%, showing 2.5 times more likely to find an intact PP than a torn PP in symptomatic individuals.

Conclusion: Interestingly, there was a low rate of abnormal PP appearance on MRI in both symptomatic and asymptomatic patients, which suggests that the chance of finding a false-positive PP tear in an asymptomatic patient is minimal and probably negligible.

Level of evidence: Level IV diagnostic.