Magnetic resonance imaging findings in bipartite medial cuneiform – a potential pitfall in diagnosis of midfoot injuries: a case series

Abstract

Introduction: The bipartite medial cuneiform is an uncommon developmental osseous variant in the midfoot. To our knowledge, Magnetic Resonance Imaging (MRI) characteristics of a nonsymptomatic bipartite medial cuneiform have not been described in the orthopaedic literature. It is important for orthopaedic foot and ankle surgeons, musculoskeletal radiologists, and for podiatrists to identify this osseous variant as it may be mistakenly diagnosed as a fracture or not recognized as a source of non-traumatic or traumatic foot pain, which may sometimes even require surgical treatment.

Symptomatic Bipartite Medial Cuneiform Treated with Fluoroscopic and Ultrasound-Guided Injections

“…The normal medial cuneiform is thought to develop from a single ossification center. However, when there are two ossification centers that fail to fuse, it results in the BMC [8,10]. With respect to the cuneiforms, ossification begins laterally during the first year of life, followed by the medial cuneiform in the second year, and finally the middle cuneiform in the third year of life [7].…”

“…However, detection on plain radiographs can be difficult as the osseous segments overlap [11], but careful evaluation of the radiographs will demonstrate two distinct often well-corticated segments in the normal position of the medial cuneiform. Cross-sectional imaging with CT or MRI is definitive in diagnosis and provides further regional anatomic detail and can be revealing of the "E sign" which is formed by the cleft between each of the segments in the horizontal plane [8]. When observed incidentally, the finding of a BMC often has no clinical significance, but should be differentiated from the numerous fracture dislocation patterns at the TMT joint level, especially the typical vertically oriented isolated fracture of the medial cuneiform that demonstrates irregular and sharp margins in contrast to the horizontally oriented well-corticated margins of the BMC [9].…”

Bipartite Medial Cuneiform and Calcaneo-Navicular Coalition in a Single Individual

“…Bipartition occurs when abnormal organisation of the primordial mesenchyme and progressing medially until complete ossification occurs around the age of 3 [4][5]8]. During this time the bipartite deformity may become apparent on imaging with a characteristic 'E-Sign' [4][5][6], which can be seen on both sagittal MRI and CT scans as demonstrated in Figure 2. The volume of a bipartite medial cuneiform is recognised as being slightly larger than that of a normal medial cuneiform with an increased dorso-plantar height of between 5-8mm [1,5,[11][12].…”

“…During early embryonic development the medial cuneiform forms either from a single or two separate portions of a single cartilaginous anlage [1,[4][5][6][7]. Bipartition occurs when abnormal organisation of the primordial mesenchyme and progressing medially until complete ossification occurs around the age of 3 [4][5]8].…”

“…Variations in the articular surfaces include a split facet for articulation of the plantar and dorsal segments with the first metatarsal, as well as that for the navicular [11][12]. The plantar segment receives the tendinous insertions of tibialis posterior and peroneus longus on its inferomedial and inferolateral surface respectively [2,6] Tibialis anterior attaches to the superomedial surface of the dorsal segment [2,6]. The dorsal segment is also the site of attachment for both the dorsal and interosseous portions of the Lisfranc ligament [2,6,8].…”