Bipartite medial cuneiform: magnetic resonance imaging findings and prevalence of this rare anatomical variant

Objective: To describe the imaging features of bipartite medial cuneiform and to determine the prevalence of this rare anatomical variant in a large group of patients that were evaluated by magnetic resonance imaging (MRI) of the foot.

Materials and method: Seven hundred and fifty-one patients that underwent MRI of the foot from May 2016 to December 2018 were included in the study (mean age 49 years; 540 females; 211 males). All MRIs were retrospectively analyzed to identify bipartite medial cuneiform. For patients with bipartite medial cuneiform, we analyzed partial and complete bipartition, the type of articulation (synchondrosis, syndesmosis, or a combination of these two), and stress changes related to abnormal motion (i.e., subchondral cysts and sclerosis). Bone marrow edema-like signal, diastasis in the cleavage plane, concomitant fractures, and the presence of the E-sign were also evaluated.

Results: Nine feet from six patients presented bipartite medial cuneiform on the MRI. Six and three feet exhibited complete and partial bipartition. All patients were referred for MRI because of midfoot pain, of which two had history of trauma prior to imaging. Stress changes related to abnormal motion were observed in three feet (34%), all with complete bipartition. Bone marrow edema-like signal was recorded in five feet (55%) and diastasis in one foot (11%). No fractures were present in the bipartite medial cuneiform. All patients had E-signs.

Conclusion: Bipartite medial cuneiform is a rare anatomical variant occurring in 0.79% of patients who underwent foot MRI in this study. It is important to be aware of this variant as it is a cause of midfoot pain. Being familiar with the E-sign helps identify and differentiate it from a fracture.