Unilateral Alar Ligament Injury: Diagnostic, Clinical, and Biomechanical Features

Abstract

Background: Isolated unilateral alar ligament injury (ALI) is a very rarely diagnosed condition, with only 9 cases reported in the literature. The purpose of this study is to determine clinical, diagnostic, and biomechanical features of unilateral ALI.

Methods: A total of 6 patients diagnosed with ALI were included in this series. The hospital records and radiologic imaging of admission and follow-ups were investigated retrospectively.

Results: Rotation of the neck and/or hyperflexion was always present as a mechanism of injury. The patients were neurologically intact. All patients presented with mild neck pain aggravated by head rotation. On computed tomography (CT) scans, the dens was observed to be displaced to the opposite side. Magnetic resonance imaging (MRI) showed a widened lateral dens-atlas space with high signal intensity. All patients underwent lateral flexion-extension CTs for the confirmation of craniovertebral junction (CVJ) stability. The patients were treated with hard collars. The follow-up MRI of 3 patients obtained at the third month showed normal lateral dens-atlas interval and recovered ligaments. All patients were pain free after 6 months.

Conclusions: Unilateral ALI appears to be more common but misdiagnosed than previously thought. Trauma mechanism consists of hyperflexion and contralateral rotation. Neck pain aggravated with rotation is the most significant clinical finding. Dens lateralization is the most important finding in CT scans. An MRI focusing on the CVJ is essential for the diagnosis. The stability of CVJ must be checked with a flexion-extension CT scan. Unilateral ALI is a stable condition and responds to conservative treatment.

Keywords: Alar ligament injury; Biomechanics; Cervical trauma; Craniovertebral junction; Flexion–extension CT; Post-traumatic neck pain.