Ligamentous instability of the first ray: A case report introducing the naviculocuneiform kissing sign on MRI scan

Abstract

Acute instability of the first ray following trauma is a rare type of Lisfranc injury. Plain radiographs may demonstrate instability if there is a clear dislocation of the first ray, however subtle injuries are difficult to recognise. Magnetic resonance imaging (MRI) has been described in the literature as an adjunct in the diagnosis of subtle Lisfranc injuries. There has been no description of the use of MRI and the unique findings of instability of the first ray in the acute setting. We report 2 cases of traumatic instability of the first ray of the foot. Both cases underwent plain radiographs, where in one patient there was a suggestive Lisfranc injury and the other patient had normal radiographical findings. Further investigation utilising an MRI showed a distinct pattern of bone bruising in the navicular and medial cuneiform at the naviculocuneiform joint. These findings indicated disruption of the ligamentous construct stabilising the first ray to the foot. Operative management was undertaken and both patients had a good outcome. This case report is important as it is the first to describe the unique MRI findings of instability of the first ray which will enable other clinicians to appropriately diagnose and manage this injury.