The Hyoid Bone in Robin Sequence: Morphology and Position in the Context of Mandibular Distraction Osteogenesis

Background: Robin Sequence (RS) is a congenital condition marked by micrognathia, glossoptosis, and airway obstruction. Patients with RS exhibit anatomical differences in the hyoid bone, a key mediator of swallowing and respiration. Severe RS is treated with mandibular distraction osteogenesis (MDO) to lengthen the mandible and increase oropharyngeal space, the latter thought to be caused by changes in hyoid position. Here, we test this hypothesis by quantitatively evaluating 3D hyoid position and morphology in patients with RS and comparing them to pediatric controls. Methods: Computed tomography (CT) scans were obtained for 38 patients with RS pre- and post-MDO and 15 control patients. Hyoid position relative to craniomandibular landmarks and hyoid morphology were compared between pre- and post-MDO RS patients and controls. Results: Pre-MDO patients have shorter relative hyoid-menton distances than post-MDOs and controls (p<0.01). Relative hyoid-basion and hyoid-vertebral column distances are comparable between groups. Controls have smaller relative hyoid-temporomandibular joint distances than RS patients (p<0.05). RS patients have a higher prevalence of abnormal hyoid ossification (control: 13.3%; pre-MDO: 36.8%) and demonstrate dimensional differences in hyoid width and angle related to both RS and MDO. Conclusions: MDO does not enlarge the oropharyngeal space by moving the hyoid anteriorly. Instead, we hypothesize MDO improves airway patency by 1) changing tongue shape and the geometry of the anterior pharyngeal wall, and 2) increasing suprahyoid muscle passive tension. Our results provide new insights into the mechanisms of mandibular distraction and highlight importance of the hyoid and its attachments in the pathologic presentation of RS.